I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!

On Fri, 11 Apr 2008 14:19:39 -0700 (PDT), EricM
wrote:

Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe.

A 600V rectifier on a 600 volt supply may not be such a safe thing to
do...

On Fri, 11 Apr 2008 14:19:39 -0700 (PDT), EricM
wrote:

I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!


You obviously need much more than 600 volt diodes. It is the PIV
which is important. What is the open circuit transformer output AC
voltage, and what is the circuit configuration used. ? You can
thencalculate the needed rating of the diodes and then add a good
safety factor.

Peter

EricM wrote:

I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!


If the DC voltage is 600 volts you need higher voltage diodes. That
is a PIV rating, not an RMS rating like they used on Selenium
Rectifiers. As a minimum you need 600 * 1+1.414 PIV. That is 600 for
the voltage across the capacitor, and 600*1.414 (848.4) volts when the
AC line reverses polarity, for a total of 1448.4 volts. That assumes
your line voltage never exceeds the rated transformer input, no spikes
from motors or other heavy loads, no lightning induced surges. As a
MINIMUM, I would use three 1000 PIV diodes in series to replace each
section of the original rectifier.


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"Michael A. Terrell" wrote in message
m...

EricM wrote:

I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!


If the DC voltage is 600 volts you need higher voltage diodes. That
is a PIV rating, not an RMS rating like they used on Selenium
Rectifiers. As a minimum you need 600 * 1+1.414 PIV. That is 600 for
the voltage across the capacitor, and 600*1.414 (848.4) volts when the
AC line reverses polarity, for a total of 1448.4 volts. That assumes
your line voltage never exceeds the rated transformer input, no spikes
from motors or other heavy loads, no lightning induced surges. As a
MINIMUM, I would use three 1000 PIV diodes in series to replace each
section of the original rectifier.



So would I, along with 10 watt wirewound resistors with a starting value of
say 1k

Arfa

Arfa Daily wrote:

"Michael A. Terrell" wrote in message
m...

EricM wrote:

I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!


If the DC voltage is 600 volts you need higher voltage diodes. That
is a PIV rating, not an RMS rating like they used on Selenium
Rectifiers. As a minimum you need 600 * 1+1.414 PIV. That is 600 for
the voltage across the capacitor, and 600*1.414 (848.4) volts when the
AC line reverses polarity, for a total of 1448.4 volts. That assumes
your line voltage never exceeds the rated transformer input, no spikes
from motors or other heavy loads, no lightning induced surges. As a
MINIMUM, I would use three 1000 PIV diodes in series to replace each
section of the original rectifier.



So would I, along with 10 watt wirewound resistors with a starting value of
say 1k


Yes, I only like to fix a problem once. Varo used to make some nice
3 KV PIV rectifiers that looked like the larger microwave oven diodes.
They were great for upgrading old broadcast and high power commercial
two wy radio systems. Using four of them and moving the meters allowed
me to reduce two full six foot racks into a single four foot outdoor
rack. It was bolted to the base of the tower and was still in use when
the owner died, years later. I did all the HV wiring with 25 KV second
anode wire.


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Yes, I only like to fix a problem once. Varo used to make some nice
3 KV PIV rectifiers that looked like the larger microwave oven diodes.
They were great for upgrading old broadcast and high power commercial
two wy radio systems. Using four of them and moving the meters allowed
me to reduce two full six foot racks into a single four foot outdoor
rack. It was bolted to the base of the tower and was still in use when
the owner died, years later. I did all the HV wiring with 25 KV second
anode wire.



Jeez, how big were the seleniums? The biggest ones I've seen were only a
couple inches square.

In article
,
EricM wrote:

I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!

Your PIV rating for the new diodes is much too low. You should have at
least a 1KV diode. Also you don't need that high a current diode.

Chuck P.

James Sweet wrote:


Yes, I only like to fix a problem once. Varo used to make some nice
3 KV PIV rectifiers that looked like the larger microwave oven diodes.
They were great for upgrading old broadcast and high power commercial
two wy radio systems. Using four of them and moving the meters allowed
me to reduce two full six foot racks into a single four foot outdoor
rack. It was bolted to the base of the tower and was still in use when
the owner died, years later. I did all the HV wiring with 25 KV second
anode wire.


Jeez, how big were the seleniums? The biggest ones I've seen were only a
couple inches square.


That determines the current. The number of plates determines the
voltage.

The Varo rectifers were epoxy cast stacked silicon that looked like
microwave oven rectifiers, but at higher current. They looked like the
NTE 541: http://www.nteinc.com/specs/500to599/pdf/nte541.pdf


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On Sat, 12 Apr 2008 00:26:07 GMT, "James Sweet"
wrote:




Yes, I only like to fix a problem once. Varo used to make some nice
3 KV PIV rectifiers that looked like the larger microwave oven diodes.
They were great for upgrading old broadcast and high power commercial
two wy radio systems. Using four of them and moving the meters allowed
me to reduce two full six foot racks into a single four foot outdoor
rack. It was bolted to the base of the tower and was still in use when
the owner died, years later. I did all the HV wiring with 25 KV second
anode wire.



Jeez, how big were the seleniums? The biggest ones I've seen were only a
couple inches square.


I've seen high current ones that were almost six inches on a side.

Pilgrim wrote:

Your PIV rating for the new diodes is much too low. You should have at
least a 1KV diode. Also you don't need that high a current diode.

Agreed. As a proof, I would check the diodes. They should be
dead now. If they are not, there's still another fault at work.
Maybe the one that caused the death of the selenium rectifier.

Regards,
H.

"PeterD" wrote in message
...
On Sat, 12 Apr 2008 00:26:07 GMT, "James Sweet"
wrote:




Yes, I only like to fix a problem once. Varo used to make some nice
3 KV PIV rectifiers that looked like the larger microwave oven diodes.
They were great for upgrading old broadcast and high power commercial
two wy radio systems. Using four of them and moving the meters allowed
me to reduce two full six foot racks into a single four foot outdoor
rack. It was bolted to the base of the tower and was still in use when
the owner died, years later. I did all the HV wiring with 25 KV second
anode wire.



Jeez, how big were the seleniums? The biggest ones I've seen were only a
couple inches square.


I've seen high current ones that were almost six inches on a side.

Old battery chargers used selenium rectifiers that there at least 6 inches
square/

"Heinz Schmitz" wrote in message
...
Pilgrim wrote:

Your PIV rating for the new diodes is much too low. You
should have at
least a 1KV diode. Also you don't need that high a current
diode.

Agreed. As a proof, I would check the diodes. They should
be
dead now. If they are not, there's still another fault at
work.
Maybe the one that caused the death of the selenium
rectifier.

Regards,
H.

One note on voltage drop of selenium rectifiers: Rectifiers
were constructed by placing a set of plates is series. The
size of the plate determined the current rating. A new
rectifier had about 1.5 volts drop per plate at rated
current. Each plate could withstand about 45 to 50 reverse
volts. Most designs pushed the reverse voltage right to the
limit. As the device aged, the forward drop would increase,
power dissipation would rise, and the stack would eventually
fail with a very obnoxious smell.

David

The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.


--

Jerry G.


"EricM" wrote in message
...
I have replaced two old Federal/ITT selenium rectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on the selenium parts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on these selenium
parts? Any leads would be greatly appreciated!

On Apr 12, 1:22 pm, "Jerry G." wrote:
The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.

--

Jerry G.

"EricM" wrote in message

...
I have replaced two old Federal/ITTseleniumrectifiers in an
amplifier power supply with new silicon diodes; the original part
numbers are 103H4AX1 and 104B1AX1. I can't find any reference to
either part on the web - anywhere - ITT can't even provide
information. Since one of the legs of the circuit supplies the plate
voltage (600V) I used 600V 10A diodes (NTE5815HC) to be safe. Problem
is, there is a time-delay relay that closes to engage the 600V
circuit, and without it attached to the amp; all tube supplies,
biasing voltage, etc. are normal. If hooked up, once the relay closes
- the main power fuse blows. I'm guessing I need a dropping resistor,
but it would be nice to have the original data on theseleniumparts
to be able to figure out the value. The 600V and the -38V biasing
voltage are derived from the same part of the power transformer. The
-38 side works, but the 600V side reads upwards of 927 volts without a
load. Using a Variac, the plate voltages were above 600V at about 70
percent. Is there a way to find the original specs on theseselenium
parts? Any leads would be greatly appreciated!

OK, I must have grotesquely underestimated the values of these, since
no literature is available. The two NTE5815HC I replaced for the
104B1AX1 seem to work fine; that part of the supply circuit has only
15 volts max capacitors in it and the output voltages seem to be fine
(12.6 for tube filaments which measure around 17 with no load, and
around 9.7 under load). The 600V side of things has two Sarkes
Tarzian 1N1239s (octal base plug-in center tapped units) in it, along
with the 600V replacement NTE5815HC that I swapped for the 103H4AX1.
From what you all have suggested, what I think is happening at this
point is that the NTE unit *has* failed once power was first applied
under load and is now conducting instead of doing what it's supposed
to, and this causes the main power fuse on the primary side of the
main transformer to sense an overload and blow. So it sounds like if
I replace this unit with one of the 3-4 KV diodes and then add a 10
watt dropping resistor to control the higher forward voltage on the
silicon unit everything should be OK? Thanks for all the input BTW!

"Jerry G." wrote in message
news:WoydnU8t2MHTYp3VnZ2dnUVZ_vWtnZ2d@uniservecomm unications...
The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.


--

Jerry G.


I'm not sure that 10 ohms is going to do too much to limit the inrush
current at these sorts of voltages, and will produce little useable running
voltage drop to compensate for the higher DC that will be produced by the
replacement silicon diodes over the original selenium stack. As far as
grafting in a 5U4 goes, I think that I would want to know a bit more about
the actual AC supply level, as this device is rated maximum 450-0-450, and
if the HT supply was up at over 600v DC off load (ie before the delay
circuit had applied the DC to the output stage) by the time that the variac
was at 70%, this would indicate that more than this was being produced by
the transformer whilst it was off load.

Depending on the voltage rating of the main filter caps, I would feel
inclined to use 3 x 1000v PIV 1 or 2 amp diodes in series, as Jerry
suggests, with a couple of high voltage 3 watt zeners in inverse series with
each rectifier string, before the filter caps. That will ensure that the
forward voltage drop of the original seleniums, which will have been taken
into consideration by the designer when he specced the caps and the output
stage supply, is effectively preserved by the replacement rectifier
arrangement. The zener value would be chosen to provide a similar drop to
that which the selenium stacks produced

Another possibility might be to use microwave oven diodes, which are also
constructed as multi-diode 'stacks', so might better emulate the original
selenium stacks for forward voltage drop. They are extremely high voltage
working and quite meaty, current-wise. I must add, however, that I have
never tried any in this sort of application, so they might have more or
less voltage drop than you need.

Jerry's advice to bypass the diodes with suitably rated caps is good, and I
would absolutely concur on that point. Also, on not re-using the diodes that
you have in there at the moment, and on making sure that there is not some
other problem that led to the demise of the seleniums. These were never the
most robust devices, if subjected to long term overload ...

Arfa

David wrote:

One note on voltage drop of selenium rectifiers: Rectifiers
were constructed by placing a set of plates is series. The
size of the plate determined the current rating. A new
rectifier had about 1.5 volts drop per plate at rated
current. Each plate could withstand about 45 to 50 reverse
volts. Most designs pushed the reverse voltage right to the
limit. As the device aged, the forward drop would increase,
power dissipation would rise, and the stack would eventually
fail with a very obnoxious smell.

I would have guessed pushing the current to the limit was more
dangerous (at the same power dissipation). The common
radio set with up to 100 mA seems to have been a safe haven
for seleniums as long as the electrolytic caps in the power supply
held or the fuse blew early enough?

Regards.
H.

On Apr 13, 3:48 pm, "Jimmie D" wrote:
"Arfa Daily" wrote in message

...





"Jerry G." wrote in message
news:WoydnU8t2MHTYp3VnZ2dnUVZ_vWtnZ2d@uniservecom munications...
The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.

--

Jerry G.

I'm not sure that 10 ohms is going to do too much to limit the inrush
current at these sorts of voltages, and will produce little useable
running voltage drop to compensate for the higher DC that will be produced
by the replacement silicon diodes over the originalseleniumstack.

I agree, 100 ohms is probably a more reasonable value.
When working on old equipment like this I try to add enough resistance to
keep the B+ at least 10% below the rating of the filer caps
If the filter caps were rated at 450 I would add enough resistors after
replacingseleniumdiodes to keep the voltage around 410 or so.
This is just kind of a best guess way of doing things when a minimum amount
of information is available.

Jimmie

First; thanks for all the insight on this. There just wasn't ANY
info out there on the original Federal parts at all. I did find a
rectifier listing on an old catalog page on a website, but these
weren't listed at all. As mentioned, the one side of the circuit
works fine. The part of the circuit in question is the 600V plate
supply for two 7027A output tubes. I'm assuming since the tube plate
current is rated from about 65ma to 450 ma there isn't a whole lot of
amperage involved here, so I do agree that the 10 amp jobs I used is
probably overkill. From the responses I'm assuming that the voltage
rating isn't enough and replacing it with a 1-4kV unit should do the
trick, along with a dropping resistor that after doing some circuit
analysis seems necessary since there is a 15K 10W resistor in series
with this part of the circuit, that is shunted by a relay switch once
a time-delay tube relay times out and powers the coil of the switching
relay - I think to enable output once the filaments of the preamp and
voltage control circuits in the amplifier are heated. It sounds like
I need a 1KV or greater diode with anywhere from 1-6 amp rating (I
found some that are 1kV 6A in the shop) and just add a dropping
resistor to get the voltage down to within spec under load.

On Apr 13, 7:34 pm, EricM wrote:
On Apr 13, 3:48 pm, "Jimmie D" wrote:



"Arfa Daily" wrote in message

...

"Jerry G." wrote in message
news:WoydnU8t2MHTYp3VnZ2dnUVZ_vWtnZ2d@uniservecom munications...
The diodes are probably breaking down. You need to have them rated at
2.8X of the voltage for the peak to peak from the AC. I would use
diodes rated to at least 3000 V to 4000 V minimum in this case because
the no load voltage is over 900 V. You can use 4 of 600 V in series to
get the proper voltage rating. I would also put caps at about 0.005 uF
/ 5 kV rated across each diode. This would be for HF noise suppression.

You should find out the required current needed for the supply load. The
diodes should be rated to at least 3X the required current at minimum.
This will allow for the inrush when the power supply is started up. The
electrolytic filter caps have to get charged up.

In series with each leg of diodes in series, I would put a 10 ohm 5 Watt
resistor in an average tube power amp supply.

If you use 1 Amp rated diodes, you can easily find diodes rated to 1000
Volts. This would allow for 900 Watts maximum load at 1000 Volts. Using
3 in series on each leg of the rectification path would be very adequate
for a 1000 Volt no load source.

I would not re-use the present diodes at this time. Most likely they may
be damaged even if they read okay.

Before going to all this trouble, make sure you find the cause of the
original rectifier failure. It may be age, but a short or something
pulling too much current should not be ruled out.

If you want to go more authentic and you have the space, get an 8 pin
octal socket, and a 5U4-GT tube. Knock out the holes in the chassis and
install the tube rectifier assembly. You will need a high voltage
isolated floating 5 Volt 2 Amp supply just for the heater. The heater is
tied hot to the cathode of this tube. You can then feed the AC 900 Volts
plate to plate, and the rectified plus source would be on the cathode.

--

Jerry G.

I'm not sure that 10 ohms is going to do too much to limit the inrush
current at these sorts of voltages, and will produce little useable
running voltage drop to compensate for the higher DC that will be produced
by the replacement silicon diodes over the originalseleniumstack.

I agree, 100 ohms is probably a more reasonable value.
When working on old equipment like this I try to add enough resistance to
keep the B+ at least 10% below the rating of the filer caps
If the filter caps were rated at 450 I would add enough resistors after
replacingseleniumdiodes to keep the voltage around 410 or so.
This is just kind of a best guess way of doing things when a minimum amount
of information is available.

Jimmie

First; thanks for all the insight on this. There just wasn't ANY
info out there on the original Federal parts at all. I did find a
rectifier listing on an old catalog page on a website, but these
weren't listed at all. As mentioned, the one side of the circuit
works fine. The part of the circuit in question is the 600V plate
supply for two 7027A output tubes. I'm assuming since the tube plate
current is rated from about 65ma to 450 ma there isn't a whole lot of
amperage involved here, so I do agree that the 10 amp jobs I used is
probably overkill. From the responses I'm assuming that the voltage
rating isn't enough and replacing it with a 1-4kV unit should do the
trick, along with a dropping resistor that after doing some circuit
analysis seems necessary since there is a 15K 10W resistor in series
with this part of the circuit, that is shunted by a relay switch once
a time-delay tube relay times out and powers the coil of the switching
relay - I think to enable output once the filaments of the preamp and
voltage control circuits in the amplifier are heated. It sounds like
I need a 1KV or greater diode with anywhere from 1-6 amp rating (I
found some that are 1kV 6A in the shop) and just add a dropping
resistor to get the voltage down to within spec under load.

I also forgot to mention that the unit in question was originally 6 -
1 inch square pieces in the stack, but only two connections. The
other unit that I replaced with the 10A 600V units was four pieces
about 1 1/8" (or just slightly larger) square, but had three
connections. This particular unit was on the 15V side of the supply
(filament supply for several 12 volt filament tubes) and the 600V 10A
silicons seem to work fine. The other part of the supply circuit -
the 600V plate supply - is where I used one of the 600V 10A jobs to
replace the 6-stack 1" square two-lead unit. Smaller but more in the
stack must have equaled more PIV handling than the 600V 10A silicon I
put where it was (with no dropping resistor). Don't know why it's so
hard to find info on these older rectifier units. They hadn't gone
bad either, I'm just replacing them to prevent filling the cutting
room with toxic stink if they should decide to fail...

I also forgot to mention that the unit in question was
originally 6 -
1 inch square pieces in the stack, but only two
connections. The
other unit that I replaced with the 10A 600V units was
four pieces
about 1 1/8" (or just slightly larger) square, but had
three
connections. This particular unit was on the 15V side of
the supply
(filament supply for several 12 volt filament tubes) and
the 600V 10A
silicons seem to work fine. The other part of the supply
circuit -
the 600V plate supply - is where I used one of the 600V
10A jobs to
replace the 6-stack 1" square two-lead unit. Smaller but
more in the
stack must have equaled more PIV handling than the 600V
10A silicon I
put where it was (with no dropping resistor). Don't know
why it's so
hard to find info on these older rectifier units. They
hadn't gone
bad either, I'm just replacing them to prevent filling the
cutting
room with toxic stink if they should decide to fail...

I admit I am very confused at this point. The three leaded
rectifier was actually two selenium diodes with a common
cathode or anode. Your replacement here should work fine but
check the filament voltage since it will be higher than
before by one or two volts. 12.6 volt tubes will not like 14
volts over a long time period.

There is no way a single 6 plate (stack) selenium rectifier
can be a half wave rectifier for a 600 volt supply. Each
rectifier plate can withstand only about 50 reverse volts
and as others have said, you need at least three times that
for a PIV rating.

David

On Apr 14, 9:27 am, "David" wrote:
I also forgot to mention that the unit in question was
originally 6 -
1 inch square pieces in the stack, but only two
connections. The
other unit that I replaced with the 10A 600V units was
four pieces
about 1 1/8" (or just slightly larger) square, but had
three
connections. This particular unit was on the 15V side of
the supply
(filament supply for several 12 volt filament tubes) and
the 600V 10A
silicons seem to work fine. The other part of the supply
circuit -
the 600V plate supply - is where I used one of the 600V
10A jobs to
replace the 6-stack 1" square two-lead unit. Smaller but
more in the
stack must have equaled more PIV handling than the 600V
10A silicon I
put where it was (with no dropping resistor). Don't know
why it's so
hard to find info on these older rectifier units. They
hadn't gone
bad either, I'm just replacing them to prevent filling the
cutting
room with toxic stink if they should decide to fail...

I admit I am very confused at this point. The three leaded
rectifier was actually twoseleniumdiodes with a common
cathode or anode. Your replacement here should work fine but
check the filament voltage since it will be higher than
before by one or two volts. 12.6 volt tubes will not like 14
volts over a long time period.

There is no way a single 6 plate (stack)seleniumrectifier
can be a half wave rectifier for a 600 volt supply. Each
rectifier plate can withstand only about 50 reverse volts
and as others have said, you need at least three times that
for a PIV rating.

David

Here's a link to the schematic; after replacing CR1 and CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure I need
dropping resistors, because the output voltage on the 12.6 and -38
terminals is very close to what it should be. Is there something I'm
missing? http://img410.imageshack.us/img410/4691/1567pscb9.jpg
Thanks.

"EricM" wrote in message
...
On Apr 14, 9:27 am, "David"
wrote:
I also forgot to mention that the unit in question was
originally 6 -
1 inch square pieces in the stack, but only two
connections. The
other unit that I replaced with the 10A 600V units was
four pieces
about 1 1/8" (or just slightly larger) square, but had
three
connections. This particular unit was on the 15V side
of
the supply
(filament supply for several 12 volt filament tubes)
and
the 600V 10A
silicons seem to work fine. The other part of the
supply
circuit -
the 600V plate supply - is where I used one of the 600V
10A jobs to
replace the 6-stack 1" square two-lead unit. Smaller
but
more in the
stack must have equaled more PIV handling than the 600V
10A silicon I
put where it was (with no dropping resistor). Don't
know
why it's so
hard to find info on these older rectifier units.
They
hadn't gone
bad either, I'm just replacing them to prevent filling
the
cutting
room with toxic stink if they should decide to fail...

I admit I am very confused at this point. The three
leaded
rectifier was actually twoseleniumdiodes with a common
cathode or anode. Your replacement here should work fine
but
check the filament voltage since it will be higher than
before by one or two volts. 12.6 volt tubes will not like
14
volts over a long time period.

There is no way a single 6 plate (stack)seleniumrectifier
can be a half wave rectifier for a 600 volt supply. Each
rectifier plate can withstand only about 50 reverse volts
and as others have said, you need at least three times
that
for a PIV rating.

David

Here's a link to the schematic; after replacing CR1 and
CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to
enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure
I need
dropping resistors, because the output voltage on the 12.6
and -38
terminals is very close to what it should be. Is there
something I'm
missing?
http://img410.imageshack.us/img410/4691/1567pscb9.jpg
Thanks.

I looked at the schematic and as I suspected, none of the
selenium rectifiers are not involved in the 600 volt supply.
CR2 A&B generate the 12.6 volt filament voltage and can be
adjusted with R1. No problem there. The other selenium
rectifier CR1 is to generate a negative bias supply.which is
also adjustable and further clamped by Zener CR3. The high
voltage is rectified by CR4 and CR5 which, I assume are
silicon diodes that you have not touched. The diodes you
used for the selenium replacement are an overkill but should
not be related to your problem. Are you sure the -38 is
really there and is in fact a minus voltage? If so, at this
point I would check the CR4 and CR5 diodes and other parts
of the 600 volt circuitry to see if you blew something else
when working on this unit.

David

"David" wrote in message
t...

"EricM" wrote in message
...
On Apr 14, 9:27 am, "David" wrote:
I also forgot to mention that the unit in question was
originally 6 -
1 inch square pieces in the stack, but only two
connections. The
other unit that I replaced with the 10A 600V units was
four pieces
about 1 1/8" (or just slightly larger) square, but had
three
connections. This particular unit was on the 15V side of
the supply
(filament supply for several 12 volt filament tubes) and
the 600V 10A
silicons seem to work fine. The other part of the supply
circuit -
the 600V plate supply - is where I used one of the 600V
10A jobs to
replace the 6-stack 1" square two-lead unit. Smaller but
more in the
stack must have equaled more PIV handling than the 600V
10A silicon I
put where it was (with no dropping resistor). Don't know
why it's so
hard to find info on these older rectifier units. They
hadn't gone
bad either, I'm just replacing them to prevent filling the
cutting
room with toxic stink if they should decide to fail...

I admit I am very confused at this point. The three leaded
rectifier was actually twoseleniumdiodes with a common
cathode or anode. Your replacement here should work fine but
check the filament voltage since it will be higher than
before by one or two volts. 12.6 volt tubes will not like 14
volts over a long time period.

There is no way a single 6 plate (stack)seleniumrectifier
can be a half wave rectifier for a 600 volt supply. Each
rectifier plate can withstand only about 50 reverse volts
and as others have said, you need at least three times that
for a PIV rating.

David

Here's a link to the schematic; after replacing CR1 and CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure I need
dropping resistors, because the output voltage on the 12.6 and -38
terminals is very close to what it should be. Is there something I'm
missing? http://img410.imageshack.us/img410/4691/1567pscb9.jpg
Thanks.

I looked at the schematic and as I suspected, none of the selenium
rectifiers are not involved in the 600 volt supply. CR2 A&B generate the
12.6 volt filament voltage and can be adjusted with R1. No problem there.
The other selenium rectifier CR1 is to generate a negative bias
supply.which is also adjustable and further clamped by Zener CR3. The high
voltage is rectified by CR4 and CR5 which, I assume are silicon diodes
that you have not touched. The diodes you used for the selenium
replacement are an overkill but should not be related to your problem. Are
you sure the -38 is really there and is in fact a minus voltage? If so, at
this point I would check the CR4 and CR5 diodes and other parts of the 600
volt circuitry to see if you blew something else when working on this
unit.

David


I wonder where exactly the 600v next goes ? I see that there is a further
1:1 transformer-isolated supply to the "regulator filament". As they've gone
to this much trouble to isolate it, could it be a regulator for the 600v
maybe ??

Arfa

EricM wrote:

Here's a link to the schematic; after replacing CR1 and CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure I need
dropping resistors, because the output voltage on the 12.6 and -38
terminals is very close to what it should be. Is there something I'm
missing? http://img410.imageshack.us/img410/4691/1567pscb9.jpg

I'd disconnect the relay (S-1 and VS3) and comfortably check all other
voltages (value, polarity, ripple). If ok, I'd power off and check the
electrolytics in the 600 V circuitry (otoh, if they do not look
exploded, they are probably ok). Then the fault is somewhere else in
the device.

BTW, what is connectors 2 on CR4 and CR5?
Does somebody switch from 8 to 2 at some point?

Regards,
H.

On Apr 16, 4:01 am, "Arfa Daily" wrote:
"David" wrote in message

t...





"EricM" wrote in message
...
On Apr 14, 9:27 am, "David" wrote:
I also forgot to mention that the unit in question was
originally 6 -
1 inch square pieces in the stack, but only two
connections. The
other unit that I replaced with the 10A 600V units was
four pieces
about 1 1/8" (or just slightly larger) square, but had
three
connections. This particular unit was on the 15V side of
the supply
(filament supply for several 12 volt filament tubes) and
the 600V 10A
silicons seem to work fine. The other part of the supply
circuit -
the 600V plate supply - is where I used one of the 600V
10A jobs to
replace the 6-stack 1" square two-lead unit. Smaller but
more in the
stack must have equaled more PIV handling than the 600V
10A silicon I
put where it was (with no dropping resistor). Don't know
why it's so
hard to find info on these older rectifier units. They
hadn't gone
bad either, I'm just replacing them to prevent filling the
cutting
room with toxic stink if they should decide to fail...

I admit I am very confused at this point. The three leaded
rectifier was actually twoseleniumdiodes with a common
cathode or anode. Your replacement here should work fine but
check the filament voltage since it will be higher than
before by one or two volts. 12.6 volt tubes will not like 14
volts over a long time period.

There is no way a single 6 plate (stack)seleniumrectifier
can be a half wave rectifier for a 600 volt supply. Each
rectifier plate can withstand only about 50 reverse volts
and as others have said, you need at least three times that
for a PIV rating.

David

Here's a link to the schematic; after replacing CR1 and CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure I need
dropping resistors, because the output voltage on the 12.6 and -38
terminals is very close to what it should be. Is there something I'm
missing?http://img410.imageshack.us/img410/4691/1567pscb9.jpg
Thanks.

I looked at the schematic and as I suspected, none of theselenium
rectifiers are not involved in the 600 volt supply. CR2 A&B generate the
12.6 volt filament voltage and can be adjusted with R1. No problem there.
The otherseleniumrectifier CR1 is to generate a negative bias
supply.which is also adjustable and further clamped by Zener CR3. The high
voltage is rectified by CR4 and CR5 which, I assume are silicon diodes
that you have not touched. The diodes you used for theselenium
replacement are an overkill but should not be related to your problem. Are
you sure the -38 is really there and is in fact a minus voltage? If so, at
this point I would check the CR4 and CR5 diodes and other parts of the 600
volt circuitry to see if you blew something else when working on this
unit.

David

I wonder where exactly the 600v next goes ? I see that there is a further
1:1 transformer-isolated supply to the "regulator filament". As they've gone
to this much trouble to isolate it, could it be a regulator for the 600v
maybe ??

Arfa

Here's a link to the rest of the device; the vacuum tube amplifier
http://www.mediafire.com/?zdmyygvyfxn It's a large image in order to
be able to scale it so you can see what's what so I needed to do
a .pdf.

On Apr 16, 7:25 am, Heinz Schmitz wrote:
EricM wrote:
Here's a link to the schematic; after replacing CR1 and CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure I need
dropping resistors, because the output voltage on the 12.6 and -38
terminals is very close to what it should be. Is there something I'm
missing? http://img410.imageshack.us/img410/4691/1567pscb9.jpg

I'd disconnect the relay (S-1 and VS3) and comfortably check all other
voltages (value, polarity, ripple). If ok, I'd power off and check the
electrolytics in the 600 V circuitry (otoh, if they do not look
exploded, they are probably ok). Then the fault is somewhere else in
the device.

BTW, what is connectors 2 on CR4 and CR5?
Does somebody switch from 8 to 2 at some point?

Regards,
H.

This is also a problem. The original 1N1239 rectifiers only have
three pins on the bottom at locations 4, 6, and 8, and the 'key'.
There is no pin on the device at #2, but the two wires from the relay
switch pole that is NC (until the coil is powered) are tied to #2 the
socket. (It's not connected to chassis ground either, which might be
inferred by the schematic - they're just meaning that two wires are
tied to #2 on the socket, even though there is no pin on the 1N1239 at
that location.) I ordered newer replacements for these from
americanmicrosemiconductor.com - they were the only place on the
internet that had exact replacements for the '1N1239' Sarkes Tarzian
center tapped rectifier. HOWEVER, when the new replacements - that
look much more like a metal envelope vacuum tube than the originals -
they have all pins and are shorter, there's no 600V on the output.
Just a few millivolts of nothing. The newer units must be wired
differently than the originals. The 1N1239 was a replacement for the
5R4 vacuum tube rectifier; I also located another online vendor that
sells 'C-Cap' rectifier replacements and he states that his 5R4
replacement should work. I'm debating whether or not to order some to
test though, since the originals seem to be oddballs of some type.
And essentially what the relay does, is shunt resistor R5, as pins 2
and 8 seem to be looped no matter what position the relay is in. This
one is really a pain - I've never encountered a PS like this one...

On 4/16/08 9:59 AM, in article
, "EricM"
wrote:

On Apr 16, 7:25 am, Heinz Schmitz wrote:
EricM wrote:
Here's a link to the schematic; after replacing CR1 and CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure I need
dropping resistors, because the output voltage on the 12.6 and -38
terminals is very close to what it should be. Is there something I'm
missing? http://img410.imageshack.us/img410/4691/1567pscb9.jpg

I'd disconnect the relay (S-1 and VS3) and comfortably check all other
voltages (value, polarity, ripple). If ok, I'd power off and check the
electrolytics in the 600 V circuitry (otoh, if they do not look
exploded, they are probably ok). Then the fault is somewhere else in
the device.

BTW, what is connectors 2 on CR4 and CR5?
Does somebody switch from 8 to 2 at some point?

Regards,
H.

This is also a problem. The original 1N1239 rectifiers only have
three pins on the bottom at locations 4, 6, and 8, and the 'key'.
There is no pin on the device at #2, but the two wires from the relay
switch pole that is NC (until the coil is powered) are tied to #2 the
socket. (It's not connected to chassis ground either, which might be
inferred by the schematic - they're just meaning that two wires are
tied to #2 on the socket, even though there is no pin on the 1N1239 at
that location.) I ordered newer replacements for these from
americanmicrosemiconductor.com - they were the only place on the
internet that had exact replacements for the '1N1239' Sarkes Tarzian
center tapped rectifier. HOWEVER, when the new replacements - that
look much more like a metal envelope vacuum tube than the originals -
they have all pins and are shorter, there's no 600V on the output.
Just a few millivolts of nothing. The newer units must be wired
differently than the originals. The 1N1239 was a replacement for the
5R4 vacuum tube rectifier; I also located another online vendor that
sells 'C-Cap' rectifier replacements and he states that his 5R4
replacement should work. I'm debating whether or not to order some to
test though, since the originals seem to be oddballs of some type.
And essentially what the relay does, is shunt resistor R5, as pins 2
and 8 seem to be looped no matter what position the relay is in. This
one is really a pain - I've never encountered a PS like this one...

All the "relay" does is to complete a low resistance path from the 600 V
voltage source, to the filter caps AFTER a time delay has (gently via 15k)
pre-charged the filter caps.

Disconnect the 600V lead from the PS to the Amp and see which way the
problem is. If the fuse still blows, trouble shoot the PS. You do have a
voltmeter?

On Apr 16, 12:30 pm, Don Bowey wrote:
On 4/16/08 9:59 AM, in article
, "EricM"



wrote:
On Apr 16, 7:25 am, Heinz Schmitz wrote:
EricM wrote:
Here's a link to the schematic; after replacing CR1 and CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure I need
dropping resistors, because the output voltage on the 12.6 and -38
terminals is very close to what it should be. Is there something I'm
missing? http://img410.imageshack.us/img410/4691/1567pscb9.jpg

I'd disconnect the relay (S-1 and VS3) and comfortably check all other
voltages (value, polarity, ripple). If ok, I'd power off and check the
electrolytics in the 600 V circuitry (otoh, if they do not look
exploded, they are probably ok). Then the fault is somewhere else in
the device.

BTW, what is connectors 2 on CR4 and CR5?
Does somebody switch from 8 to 2 at some point?

Regards,
H.

This is also a problem. The original 1N1239 rectifiers only have
three pins on the bottom at locations 4, 6, and 8, and the 'key'.
There is no pin on the device at #2, but the two wires from the relay
switch pole that is NC (until the coil is powered) are tied to #2 the
socket. (It's not connected to chassis ground either, which might be
inferred by the schematic - they're just meaning that two wires are
tied to #2 on the socket, even though there is no pin on the 1N1239 at
that location.) I ordered newer replacements for these from
americanmicrosemiconductor.com - they were the only place on the
internet that had exact replacements for the '1N1239' Sarkes Tarzian
center tapped rectifier. HOWEVER, when the new replacements - that
look much more like a metal envelope vacuum tube than the originals -
they have all pins and are shorter, there's no 600V on the output.
Just a few millivolts of nothing. The newer units must be wired
differently than the originals. The 1N1239 was a replacement for the
5R4 vacuum tube rectifier; I also located another online vendor that
sells 'C-Cap' rectifier replacements and he states that his 5R4
replacement should work. I'm debating whether or not to order some to
test though, since the originals seem to be oddballs of some type.
And essentially what the relay does, is shunt resistor R5, as pins 2
and 8 seem to be looped no matter what position the relay is in. This
one is really a pain - I've never encountered a PS like this one...

All the "relay" does is to complete a low resistance path from the 600 V
voltage source, to the filter caps AFTER a time delay has (gently via 15k)
pre-charged the filter caps.

Disconnect the 600V lead from the PS to the Amp and see which way the
problem is. If the fuse still blows, trouble shoot the PS. You do have a
voltmeter?

Yes, the weird part about this is that before doing any work on the
power supplies (i.e. everything working) the output voltages with no
load were around 17 on the 12.6 legs, -38 on the bias, 6.7 - 7.2 on
the 6.3 volt legs, and nearly 930V on the "600" output. I used a
Variac to bring things up slowly after doing the modifications to
check the output and it was nearly the same on all outputs (again, no
load). Hooked the cables up to the amp and used a Variac again, and
the 17 was pulled down to around 9.7 once under load, the -38 remained
about the same, the filament voltages were all within 6.3 - 7.1V, and
the plate side of the output transformer read about 500V, but once the
voltage got nearly up to full input voltage and the relay closed
(110-120) the 5A fuse popped. If I disconnect the 600V connection at
the amp - the fuse doesn't blow. The amps and components test fine
and no changes have been made there since everything was working.

One thought though, and I'm not sure if it makes sense or not; I
measured the resistance of the selenium I removed in the bias circuit
- which shares the "common" with the 600V supply - and it was about
1.4 Meg. The resistance across the silicon diode I replaced it with
is only around 830K. Forward voltage drop aside - is it possible that
since the new component doesn't have the same resistance
characteristic as the new that adding a "dropping resistor" per se
would increase the resistance and balance out the circuit? I've put a
1/2 watt 330K resistor in series with one of the 10A 600V diodes that
I used, and the resistance then measures around 1.4 Meg, but I doubt a
1/2 watt unit would stand up to the circuit load. I'd probably have
to have at least a 10W unit, and 330K in 10W is hard to locate. Does
this make sense? I'm running out of ideas with this thing... :/

On 4/16/08 12:11 PM, in article
, "EricM"
wrote:

On Apr 16, 12:30 pm, Don Bowey wrote:
On 4/16/08 9:59 AM, in article
, "EricM"



wrote:
On Apr 16, 7:25 am, Heinz Schmitz wrote:
EricM wrote:
Here's a link to the schematic; after replacing CR1 and CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure I need
dropping resistors, because the output voltage on the 12.6 and -38
terminals is very close to what it should be. Is there something I'm
missing? http://img410.imageshack.us/img410/4691/1567pscb9.jpg

I'd disconnect the relay (S-1 and VS3) and comfortably check all other
voltages (value, polarity, ripple). If ok, I'd power off and check the
electrolytics in the 600 V circuitry (otoh, if they do not look
exploded, they are probably ok). Then the fault is somewhere else in
the device.

BTW, what is connectors 2 on CR4 and CR5?
Does somebody switch from 8 to 2 at some point?

Regards,
H.

This is also a problem. The original 1N1239 rectifiers only have
three pins on the bottom at locations 4, 6, and 8, and the 'key'.
There is no pin on the device at #2, but the two wires from the relay
switch pole that is NC (until the coil is powered) are tied to #2 the
socket. (It's not connected to chassis ground either, which might be
inferred by the schematic - they're just meaning that two wires are
tied to #2 on the socket, even though there is no pin on the 1N1239 at
that location.) I ordered newer replacements for these from
americanmicrosemiconductor.com - they were the only place on the
internet that had exact replacements for the '1N1239' Sarkes Tarzian
center tapped rectifier. HOWEVER, when the new replacements - that
look much more like a metal envelope vacuum tube than the originals -
they have all pins and are shorter, there's no 600V on the output.
Just a few millivolts of nothing. The newer units must be wired
differently than the originals. The 1N1239 was a replacement for the
5R4 vacuum tube rectifier; I also located another online vendor that
sells 'C-Cap' rectifier replacements and he states that his 5R4
replacement should work. I'm debating whether or not to order some to
test though, since the originals seem to be oddballs of some type.
And essentially what the relay does, is shunt resistor R5, as pins 2
and 8 seem to be looped no matter what position the relay is in. This
one is really a pain - I've never encountered a PS like this one...

All the "relay" does is to complete a low resistance path from the 600 V
voltage source, to the filter caps AFTER a time delay has (gently via 15k)
pre-charged the filter caps.

Disconnect the 600V lead from the PS to the Amp and see which way the
problem is. If the fuse still blows, trouble shoot the PS. You do have a
voltmeter?

Yes, the weird part about this is that before doing any work on the
power supplies (i.e. everything working) the output voltages with no
load were around 17 on the 12.6 legs, -38 on the bias, 6.7 - 7.2 on
the 6.3 volt legs, and nearly 930V on the "600" output. I used a
Variac to bring things up slowly after doing the modifications to
check the output and it was nearly the same on all outputs (again, no
load). Hooked the cables up to the amp and used a Variac again, and
the 17 was pulled down to around 9.7 once under load, the -38 remained
about the same, the filament voltages were all within 6.3 - 7.1V, and
the plate side of the output transformer read about 500V, but once the
voltage got nearly up to full input voltage and the relay closed
(110-120) the 5A fuse popped. If I disconnect the 600V connection at
the amp - the fuse doesn't blow. The amps and components test fine
and no changes have been made there since everything was working.

One thought though, and I'm not sure if it makes sense or not; I
measured the resistance of the selenium I removed in the bias circuit
- which shares the "common" with the 600V supply - and it was about
1.4 Meg.

Measured in or out of the circuit? Forward or reverse? At what voltage was
the resistance measured? It's been a while since I worked on anything using
a selenium stack, but....... They age. The forward resistance goes up. I
was not ever impressed with the reverse resistance, and 1.4 Meg might be ok.
When changing them out with silicon, I always added a series resistor. As I
recall, I commonly used about 300 Ohms for a 75 to 100 mA selenium
change-out, but 50 to 100 Ohms might be more appropriate for this PS


The resistance across the silicon diode I replaced it with
is only around 830K.

That is too Low. The forward resistance should be only a few Ohms, and the
reverse will be many MegOhms.

Forward voltage drop aside - is it possible that
since the new component doesn't have the same resistance
characteristic as the new that adding a "dropping resistor" per se
would increase the resistance and balance out the circuit? I've put a
1/2 watt 330K resistor in series with one of the 10A 600V diodes that
I used, and the resistance then measures around 1.4 Meg, but I doubt a
1/2 watt unit would stand up to the circuit load. I'd probably have
to have at least a 10W unit, and 330K in 10W is hard to locate. Does
this make sense? I'm running out of ideas with this thing... :/

Putting that much resistance in series with the diode renders it useless.
The Amp is going to draw a lot of current, so any resistance needs to be
relatively low, and it needs to have a much higher power rating. Ohm's Law
is your friend.

Recheck your silicon diode's front and back resistances. If they don't
agree with what I posted above, either they are defective or your test
voltage is not suitable.

It may be that one of the filter caps is breaking down. Do you have any
spare 40 to 80 Mfd, 400V caps?

Don

"EricM" wrote in message
...
On Apr 16, 4:01 am, "Arfa Daily" wrote:
"David" wrote in message

t...





"EricM" wrote in message
...
On Apr 14, 9:27 am, "David" wrote:
I also forgot to mention that the unit in question was
originally 6 -
1 inch square pieces in the stack, but only two
connections. The
other unit that I replaced with the 10A 600V units was
four pieces
about 1 1/8" (or just slightly larger) square, but had
three
connections. This particular unit was on the 15V side of
the supply
(filament supply for several 12 volt filament tubes) and
the 600V 10A
silicons seem to work fine. The other part of the supply
circuit -
the 600V plate supply - is where I used one of the 600V
10A jobs to
replace the 6-stack 1" square two-lead unit. Smaller but
more in the
stack must have equaled more PIV handling than the 600V
10A silicon I
put where it was (with no dropping resistor). Don't know
why it's so
hard to find info on these older rectifier units. They
hadn't gone
bad either, I'm just replacing them to prevent filling the
cutting
room with toxic stink if they should decide to fail...

I admit I am very confused at this point. The three leaded
rectifier was actually twoseleniumdiodes with a common
cathode or anode. Your replacement here should work fine but
check the filament voltage since it will be higher than
before by one or two volts. 12.6 volt tubes will not like 14
volts over a long time period.

There is no way a single 6 plate (stack)seleniumrectifier
can be a half wave rectifier for a 600 volt supply. Each
rectifier plate can withstand only about 50 reverse volts
and as others have said, you need at least three times that
for a PIV rating.

David

Here's a link to the schematic; after replacing CR1 and CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure I need
dropping resistors, because the output voltage on the 12.6 and -38
terminals is very close to what it should be. Is there something I'm
missing?http://img410.imageshack.us/img410/4691/1567pscb9.jpg
Thanks.

I looked at the schematic and as I suspected, none of theselenium
rectifiers are not involved in the 600 volt supply. CR2 A&B generate
the
12.6 volt filament voltage and can be adjusted with R1. No problem
there.
The otherseleniumrectifier CR1 is to generate a negative bias
supply.which is also adjustable and further clamped by Zener CR3. The
high
voltage is rectified by CR4 and CR5 which, I assume are silicon diodes
that you have not touched. The diodes you used for theselenium
replacement are an overkill but should not be related to your problem.
Are
you sure the -38 is really there and is in fact a minus voltage? If so,
at
this point I would check the CR4 and CR5 diodes and other parts of the
600
volt circuitry to see if you blew something else when working on this
unit.

David

I wonder where exactly the 600v next goes ? I see that there is a further
1:1 transformer-isolated supply to the "regulator filament". As they've
gone
to this much trouble to isolate it, could it be a regulator for the 600v
maybe ??

Arfa

Here's a link to the rest of the device; the vacuum tube amplifier
http://www.mediafire.com/?zdmyygvyfxn It's a large image in order to
be able to scale it so you can see what's what so I needed to do
a .pdf.

Assuming that the power supply runs without blowing the fuse, when it is
disconnected from the power amp, then looking at the schematic, it seems to
me that tracking down the problem will be relatively simple. But before
going any further down that route, can we get a bit clearer on how exactly
you have gotten to the point that you are at now? First, did the psu / amp
combination ever work before you started work on it, or has it been blowing
fuses all along ? The LT selenium reccies that you replaced just for
reliability's sake can be discounted I think. What was the reasoning behind
replacing the HT rectifier packs ? As you imply that these are differently
wired from the originals, could this be anything to do with the current
problems ? I'm sure that you have described some of this reasoning elsewhere
in the thread in odd bits, but it would be helpful if you could just go
through the whole of how you have reached the point you are now at, all in
one go.

Arfa

"Don Bowey" wrote in message
...
On 4/16/08 12:11 PM, in article
, "EricM"
wrote:

On Apr 16, 12:30 pm, Don Bowey wrote:
On 4/16/08 9:59 AM, in article
,
"EricM"



wrote:
On Apr 16, 7:25 am, Heinz Schmitz wrote:
EricM wrote:
Here's a link to the schematic; after replacing CR1 and CR2A/B with
10 amp 600 V silicon diodes, when the relay closes to enable the 600V
plate voltage, the main power fuse F1 blows. I'm not sure I need
dropping resistors, because the output voltage on the 12.6 and -38
terminals is very close to what it should be. Is there something I'm
missing? http://img410.imageshack.us/img410/4691/1567pscb9.jpg

I'd disconnect the relay (S-1 and VS3) and comfortably check all other
voltages (value, polarity, ripple). If ok, I'd power off and check the
electrolytics in the 600 V circuitry (otoh, if they do not look
exploded, they are probably ok). Then the fault is somewhere else in
the device.

BTW, what is connectors 2 on CR4 and CR5?
Does somebody switch from 8 to 2 at some point?

Regards,
H.

This is also a problem. The original 1N1239 rectifiers only have
three pins on the bottom at locations 4, 6, and 8, and the 'key'.
There is no pin on the device at #2, but the two wires from the relay
switch pole that is NC (until the coil is powered) are tied to #2 the
socket. (It's not connected to chassis ground either, which might be
inferred by the schematic - they're just meaning that two wires are
tied to #2 on the socket, even though there is no pin on the 1N1239 at
that location.) I ordered newer replacements for these from
americanmicrosemiconductor.com - they were the only place on the
internet that had exact replacements for the '1N1239' Sarkes Tarzian
center tapped rectifier. HOWEVER, when the new replacements - that
look much more like a metal envelope vacuum tube than the originals -
they have all pins and are shorter, there's no 600V on the output.
Just a few millivolts of nothing. The newer units must be wired
differently than the originals. The 1N1239 was a replacement for the
5R4 vacuum tube rectifier; I also located another online vendor that
sells 'C-Cap' rectifier replacements and he states that his 5R4
replacement should work. I'm debating whether or not to order some to
test though, since the originals seem to be oddballs of some type.
And essentially what the relay does, is shunt resistor R5, as pins 2
and 8 seem to be looped no matter what position the relay is in. This
one is really a pain - I've never encountered a PS like this one...

All the "relay" does is to complete a low resistance path from the 600 V
voltage source, to the filter caps AFTER a time delay has (gently via
15k)
pre-charged the filter caps.

Disconnect the 600V lead from the PS to the Amp and see which way the
problem is. If the fuse still blows, trouble shoot the PS. You do have
a
voltmeter?

Yes, the weird part about this is that before doing any work on the
power supplies (i.e. everything working) the output voltages with no
load were around 17 on the 12.6 legs, -38 on the bias, 6.7 - 7.2 on
the 6.3 volt legs, and nearly 930V on the "600" output. I used a
Variac to bring things up slowly after doing the modifications to
check the output and it was nearly the same on all outputs (again, no
load). Hooked the cables up to the amp and used a Variac again, and
the 17 was pulled down to around 9.7 once under load, the -38 remained
about the same, the filament voltages were all within 6.3 - 7.1V, and
the plate side of the output transformer read about 500V, but once the
voltage got nearly up to full input voltage and the relay closed
(110-120) the 5A fuse popped. If I disconnect the 600V connection at
the amp - the fuse doesn't blow. The amps and components test fine
and no changes have been made there since everything was working.

One thought though, and I'm not sure if it makes sense or not; I
measured the resistance of the selenium I removed in the bias circuit
- which shares the "common" with the 600V supply - and it was about
1.4 Meg.

Measured in or out of the circuit? Forward or reverse? At what voltage
was
the resistance measured? It's been a while since I worked on anything
using
a selenium stack, but....... They age. The forward resistance goes up.
I
was not ever impressed with the reverse resistance, and 1.4 Meg might be
ok.
When changing them out with silicon, I always added a series resistor. As
I
recall, I commonly used about 300 Ohms for a 75 to 100 mA selenium
change-out, but 50 to 100 Ohms might be more appropriate for this PS


The resistance across the silicon diode I replaced it with
is only around 830K.

Forward voltage drop aside - is it possible that
since the new component doesn't have the same resistance
characteristic as the new that adding a "dropping resistor" per se
would increase the resistance and balance out the circuit? I've put a
1/2 watt 330K resistor in series with one of the 10A 600V diodes that
I used, and the resistance then measures around 1.4 Meg, but I doubt a
1/2 watt unit would stand up to the circuit load. I'd probably have
to have at least a 10W unit, and 330K in 10W is hard to locate. Does
this make sense? I'm running out of ideas with this thing... :/


The forward resistance of a typical silicon diode will be about 700 ohms to
1k ohm, measured on a typical analogue multimeter. Reverse resistance will
be, to all intents and purposes, infinity.

Reading again where you currently are, and how you got there, it seems that
before you started 'modifying' the rig, it worked. The only implication of
this is that the current problem must be down to something you have done
yourself. Looking at the sorts of values of resistor that you are trying to
work with, it is clear that your understanding of how this equipment should
work, is a little sketchy. Whilst tube based equipment is actually very
simple in design concept, and normally a breeze to troubleshoot, it is
actually quite 'specialist', and if you are not used to working on it,
regrettably, you may be getting yourself out of your depth on this one.

Unless you have a clear idea of exactly how to troubleshoot the problem, I
think that it might be time to abandon your efforts, and call in some
on-the-spot help. I'm not trying to deliberately put you off - or put you
down even - just offering some good honest advice with the experience of
many years at this.

Arfa

EricM wrote:

BTW, what is connectors 2 on CR4 and CR5?
Does somebody switch from 8 to 2 at some point?

The 1N1239 was a replacement for the
5R4 vacuum tube rectifier;

Oh, that explains it. Then the 5R4 ist a directly heated rectifier
tube and the 5 Volts AC are the heater power. This is, you may
disconnect 12 and 13 from the mains transformer when using
selenium or other semiconductor rectifiers.

I also located another online vendor that
sells 'C-Cap' rectifier replacements and he states that his 5R4
replacement should work. I'm debating whether or not to order some to
test though,

Investments into faulty equipment mostly turn out wrong, if a sound
reason for the purchase is not present :-).

And essentially what the relay does, is shunt resistor R5,

To give the amp tubes time to heat up before anode etc power is
applied. Very reasonable.

as pins 2
and 8 seem to be looped no matter what position the relay is in. This
one is really a pain - I've never encountered a PS like this one...

It looks quite ok once we understand everything :-).

Now, once the power supply seems to be ok, I would follow the 600 V
wiring into the amp with an Ohm-Meter and try to locate a low
resitance to ground.
Next I would check all anode-to-grid caps like eg C19 at V8b. If some
of those leak, the grid will not be negative enough and anode current
will go through the roof.
I'd disconnect T2 on the primary side and measure the resistance of
the windings and the resistance to ground, to prove that the
transformer is still ok.

Well, much everything like in a common radio repair :-).

Regards,
H.

On Apr 17, 6:35 am, Heinz Schmitz wrote:
EricM wrote:
BTW, what is connectors 2 on CR4 and CR5?
Does somebody switch from 8 to 2 at some point?

The 1N1239 was a replacement for the
5R4 vacuum tube rectifier;

Oh, that explains it. Then the 5R4 ist a directly heated rectifier
tube and the 5 Volts AC are the heater power. This is, you may
disconnect 12 and 13 from the mains transformer when usingseleniumor other semiconductor rectifiers.

I also located another online vendor that
sells 'C-Cap' rectifier replacements and he states that his 5R4
replacement should work. I'm debating whether or not to order some to
test though,

Investments into faulty equipment mostly turn out wrong, if a sound
reason for the purchase is not present :-).

And essentially what the relay does, is shunt resistor R5,

To give the amp tubes time to heat up before anode etc power is
applied. Very reasonable.

as pins 2
and 8 seem to be looped no matter what position the relay is in. This
one is really a pain - I've never encountered a PS like this one...

It looks quite ok once we understand everything :-).

Now, once the power supply seems to be ok, I would follow the 600 V
wiring into the amp with an Ohm-Meter and try to locate a low
resitance to ground.
Next I would check all anode-to-grid caps like eg C19 at V8b. If some
of those leak, the grid will not be negative enough and anode current
will go through the roof.
I'd disconnect T2 on the primary side and measure the resistance of
the windings and the resistance to ground, to prove that the
transformer is still ok.

Well, much everything like in a common radio repair :-).

Regards,
H.

Actually made some progress. Yes, a previous poster was correct that
my understanding is "sketchy" That's why I'm posting here...

I didn't replace the large Sarkes Tarzians, but did replace the
selenium stacks. I do intend to put 5R4's back in the PS for
rectifiers though, as due to their age they may be contributing to the
overvoltage in the 600V circuit (i.e. reading 900+ when all's supposed
to be present is around 600). Have since found out from another tech
that the silicon's I used elsewhere in the PS circuit are no problem
since they're not part of the HV circuit, and their output voltages
under load measure normal. Will add a small dropping resistor though
to prevent damage to the tubes. One problem was that there was a cap
in the 600V circuit on the amp side that was conducting - basically a
600V to ground. Not good, and was causing the fuse to blow. Replaced
it and got the amp functioning and not blowing fuses, but after
applying a test signal from a tone generator, something 'opened' and I
am getting some 60 hz buzz in the output, which I think might be one
or both of the two 80/450 caps in the power supply that were damaged
by the fuse blowing several times during troubleshooting. In
addition, I did find that two other caps in the amp were getting bad
(old can electrolytics) - made "new" ones and things got better, but
still 'buzzing'. I also suspect some of the old can caps (lower
voltages) in the power supply in addition to the large 450V units, as
at this point there isn't anything else in the amp that is old and
could be shorting or leaking. All of the signal caps have been
replaced with Auricaps. Been a lot of work, but I think I'm close to
completing the project.

On Apr 19, 9:37 pm, EricM wrote:
On Apr 17, 6:35 am, Heinz Schmitz wrote:



EricM wrote:
BTW, what is connectors 2 on CR4 and CR5?
Does somebody switch from 8 to 2 at some point?

The 1N1239 was a replacement for the
5R4 vacuum tube rectifier;

Oh, that explains it. Then the 5R4 ist a directly heated rectifier
tube and the 5 Volts AC are the heater power. This is, you may
disconnect 12 and 13 from the mains transformer when usingseleniumor other semiconductor rectifiers.

I also located another online vendor that
sells 'C-Cap' rectifier replacements and he states that his 5R4
replacement should work. I'm debating whether or not to order some to
test though,

Investments into faulty equipment mostly turn out wrong, if a sound
reason for the purchase is not present :-).

And essentially what the relay does, is shunt resistor R5,

To give the amp tubes time to heat up before anode etc power is
applied. Very reasonable.

as pins 2
and 8 seem to be looped no matter what position the relay is in. This
one is really a pain - I've never encountered a PS like this one...

It looks quite ok once we understand everything :-).

Now, once the power supply seems to be ok, I would follow the 600 V
wiring into the amp with an Ohm-Meter and try to locate a low
resitance to ground.
Next I would check all anode-to-grid caps like eg C19 at V8b. If some
of those leak, the grid will not be negative enough and anode current
will go through the roof.
I'd disconnect T2 on the primary side and measure the resistance of
the windings and the resistance to ground, to prove that the
transformer is still ok.

Well, much everything like in a common radio repair :-).

Regards,
H.

Actually made some progress. Yes, a previous poster was correct that
my understanding is "sketchy" That's why I'm posting here...

I didn't replace the large Sarkes Tarzians, but did replace theseleniumstacks. I do intend to put 5R4's back in the PS for
rectifiers though, as due to their age they may be contributing to the
overvoltage in the 600V circuit (i.e. reading 900+ when all's supposed
to be present is around 600). Have since found out from another tech
that the silicon's I used elsewhere in the PS circuit are no problem
since they're not part of the HV circuit, and their output voltages
under load measure normal. Will add a small dropping resistor though
to prevent damage to the tubes. One problem was that there was a cap
in the 600V circuit on the amp side that was conducting - basically a
600V to ground. Not good, and was causing the fuse to blow. Replaced
it and got the amp functioning and not blowing fuses, but after
applying a test signal from a tone generator, something 'opened' and I
am getting some 60 hz buzz in the output, which I think might be one
or both of the two 80/450 caps in the power supply that were damaged
by the fuse blowing several times during troubleshooting. In
addition, I did find that two other caps in the amp were getting bad
(old can electrolytics) - made "new" ones and things got better, but
still 'buzzing'. I also suspect some of the old can caps (lower
voltages) in the power supply in addition to the large 450V units, as
at this point there isn't anything else in the amp that is old and
could be shorting or leaking. All of the signal caps have been
replaced with Auricaps. Been a lot of work, but I think I'm close to
completing the project.

Forgot to mention that the 'buzzing' only starts after the relay
closes - so more evidence that it's either the 80/450's in the PS, or
possibly a problem somewhere around the voltage divider/0A2/6DR7
portion of the circuit that is fed from the 600V terminal in the amp.

On Sat, 19 Apr 2008 19:42:23 -0700 (PDT), EricM
wrote:


Forgot to mention that the 'buzzing' only starts after the relay
closes - so more evidence that it's either the 80/450's in the PS, or
possibly a problem somewhere around the voltage divider/0A2/6DR7
portion of the circuit that is fed from the 600V terminal in the amp.


Not possible that it is the relay itself that is mechanically buzzing
perhaps?

Peter

On Apr 20, 5:15 am, Peter Dettmann wrote:
On Sat, 19 Apr 2008 19:42:23 -0700 (PDT), EricM
wrote:



Forgot to mention that the 'buzzing' only starts after the relay
closes - so more evidence that it's either the 80/450's in the PS, or
possibly a problem somewhere around the voltage divider/0A2/6DR7
portion of the circuit that is fed from the 600V terminal in the amp.

Not possible that it is the relay itself that is mechanically buzzing
perhaps?

Peter

The relay itself isn't making any noise; it did 'buzz' a little
before the fuse blew prior to fixing that problem, but it's a 60hz
noise in the speaker now. Suspect the PS since most everything in the
amp that could leak 60hz has been replaced.

"EricM" wrote in message
...
On Apr 20, 5:15 am, Peter Dettmann wrote:
On Sat, 19 Apr 2008 19:42:23 -0700 (PDT), EricM
wrote:



Forgot to mention that the 'buzzing' only starts after the relay
closes - so more evidence that it's either the 80/450's in the PS, or
possibly a problem somewhere around the voltage divider/0A2/6DR7
portion of the circuit that is fed from the 600V terminal in the amp.

Not possible that it is the relay itself that is mechanically buzzing
perhaps?

Peter

The relay itself isn't making any noise; it did 'buzz' a little
before the fuse blew prior to fixing that problem, but it's a 60hz
noise in the speaker now. Suspect the PS since most everything in the
amp that could leak 60hz has been replaced.

Is the buzz affected by the volume control ?

Arfa

On Apr 20, 8:04 pm, "Arfa Daily" wrote:
"EricM" wrote in message

...



On Apr 20, 5:15 am, Peter Dettmann wrote:
On Sat, 19 Apr 2008 19:42:23 -0700 (PDT), EricM
wrote:

Forgot to mention that the 'buzzing' only starts after the relay
closes - so more evidence that it's either the 80/450's in the PS, or
possibly a problem somewhere around the voltage divider/0A2/6DR7
portion of the circuit that is fed from the 600V terminal in the amp.

Not possible that it is the relay itself that is mechanically buzzing
perhaps?

Peter

The relay itself isn't making any noise; it did 'buzz' a little
before the fuse blew prior to fixing that problem, but it's a 60hz
noise in the speaker now. Suspect the PS since most everything in the
amp that could leak 60hz has been replaced.

Is the buzz affected by the volume control ?

Arfa

There is no volume control as this is a power amp only, however
increasing or decreasing the input signal doesn't affect the buzzing.
Just a 60Hz drone...

On Sun, 20 Apr 2008 19:00:58 -0700 (PDT), EricM
wrote:



Is the buzz affected by the volume control ?

Arfa

There is no volume control as this is a power amp only, however
increasing or decreasing the input signal doesn't affect the buzzing.
Just a 60Hz drone...

It helps if you can check with a CRO to find if it is 60Hz or 120 Hz
(120Hz will come from inadequate filtering in the power supply).

Work back wards logically to find the source. Initially leave only
the output circuit feeding the speaker, and see if the Hum is still
there. Then keep adding stages back to the input till the hum
returns. You are then better able to analyse the situation.

Peter

EricM wrote:

Forgot to mention that the 'buzzing' only starts after the relay
closes -

Well of course it does, because before that the amp isn't working at
all. A tube amp without anode voltage is just a refined heater.

Do not forget that this is a tube device. Some of the tube cathodes
are heated with 6.3 Volts alternating current of 60 Hz. If there is a
cathode-heater-leak (due to tube age) you get AC into the signal path.

Note that the preamp stages are operated with 400 Volts off the
stabilizer circuit around V9 - V10. So have a look at C20 / C2 - they
should neutralize AC ripple there.

I'm scratching my head about connectors 3 and 4 on TS2 named
regulator filament. Somehow TS2 in the ps-schematic doesn't seem
to be TS2 in the amp schematic.

Regards,
H.