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.


--
aioe.org is home to cowards and terrorists

Add this line to your news proxy nfilter.dat file
* drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic.

http://improve-usenet.org/index.html


Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

"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.


--
aioe.org is home to cowards and terrorists

Add this line to your news proxy nfilter.dat file
* drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic.

http://improve-usenet.org/index.html


Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

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.

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


--
aioe.org is home to cowards and terrorists

Add this line to your news proxy nfilter.dat file
* drop Path:*aioe.org!not-for-mail to drop all aioe.org traffic.

http://improve-usenet.org/index.html


Use any search engine other than Google till they stop polluting USENET
with porn and junk commercial SPAM

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.

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.

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.

"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

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.

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