**Hi to the amp techs,

there is something odd about the HEATERS in current production EH branded
valves.

If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between pins 4
and 5.

Check any other brand and the reading is 10 to 14 ohms.

The EH ones still draw 160mA at 12.6 volts like the others.

Similar but smaller differences exist with EL34EHs and 6V6EHs too.

That Bugera I posted about a few days back would NOT have developed the
nasty AC fuse blowing fault it did if EH brand 12AX7s were fitted - as the
start up heater current would be 3 times less.



.... Phil

"Phil Allison" wrote in message
...

**Hi to the amp techs,

there is something odd about the HEATERS in current production EH branded
valves.

If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between pins
4 and 5.

Check any other brand and the reading is 10 to 14 ohms.

The EH ones still draw 160mA at 12.6 volts like the others.

Similar but smaller differences exist with EL34EHs and 6V6EHs too.

That Bugera I posted about a few days back would NOT have developed the
nasty AC fuse blowing fault it did if EH brand 12AX7s were fitted - as
the start up heater current would be 3 times less.



... Phil




So what's your theory ? It seems a contradiction that the heater can have
three times the resistance, but still draw the same current ? Maybe the
material that they've made it out of has a different resistance v
temperature characteristic that decreases as the temperature increases to
get back to the same running hot resistance as other makes once they have
warmed up and their heater resistance has increased as a result, although
I'm not sure what - if any - metal has such a characteristic. I suppose it
would act a bit like the heater thermistor that we had in the old days of
valve TV sets, to stop the heaters coming up like torch bulbs at switch on.

How about hooking one of each to a variable DC bench supply, and seeing what
happens to the current as the voltage is gently turned up. It would also be
interesting to look to see if there *is* any surge current when full voltage
is applied from cold.

Interestingly, I used to have great faith in EH valves, but of late, I've
found them to not be anything like as reliable as I think they were a couple
of years ago. Maybe they're getting them from a different manufacturer now ?
Do you happen to know anything about who's valves they actually are ?

Arfa

"Arfa Daily"
"Phil Allison"

**Hi to the amp techs,

there is something odd about the HEATERS in current production EH branded
valves.

If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between pins
4 and 5.

Check any other brand and the reading is 10 to 14 ohms.

The EH ones still draw 160mA at 12.6 volts like the others.

Similar but smaller differences exist with EL34EHs and 6V6EHs too.

That Bugera I posted about a few days back would NOT have developed the
nasty AC fuse blowing fault it did if EH brand 12AX7s were fitted - as
the start up heater current would be 3 times less.


So what's your theory ?


** I thought it was obvious.

The filament wire is not made from tungsten, as in all the others.


How about hooking one of each to a variable DC bench supply, and seeing
what happens to the current as the voltage is gently turned up. It would
also be interesting to look to see if there *is* any surge current when
full voltage is applied from cold.

** Been there, done that.

12.6 volts at 160 mA = 79 ohms.

Duhhh ..............


Interestingly, I used to have great faith in EH valves, but of late, I've
found them to not be anything like as reliable as I think they were a
couple of years ago. Maybe they're getting them from a different
manufacturer now ? Do you happen to know anything about who's valves they
actually are ?

** Same valves previously sold a "Sovtek " far as I know.


BTW: Ever see a " Sovtek " amplifier ?

Like the MIG100 or MIG 60.

The couple I've seen were amazing pieces of work - no PCB, laced wiring,
ceramic sockets, heavy as hell and full of MIL high parts.

Like something built for the Russian military.



.... Phil

On 24/08/2013 10:30, Arfa Daily wrote:


"Phil Allison" wrote in message
...

**Hi to the amp techs,

there is something odd about the HEATERS in current production EH
branded valves.

If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between
pins 4 and 5.

Check any other brand and the reading is 10 to 14 ohms.

The EH ones still draw 160mA at 12.6 volts like the others.

Similar but smaller differences exist with EL34EHs and 6V6EHs too.

That Bugera I posted about a few days back would NOT have developed
the nasty AC fuse blowing fault it did if EH brand 12AX7s were fitted
- as the start up heater current would be 3 times less.



... Phil




So what's your theory ? It seems a contradiction that the heater can
have three times the resistance, but still draw the same current ? Maybe
the material that they've made it out of has a different resistance v
temperature characteristic that decreases as the temperature increases
to get back to the same running hot resistance as other makes once they
have warmed up and their heater resistance has increased as a result,
although I'm not sure what - if any - metal has such a characteristic. I
suppose it would act a bit like the heater thermistor that we had in the
old days of valve TV sets, to stop the heaters coming up like torch
bulbs at switch on.

How about hooking one of each to a variable DC bench supply, and seeing
what happens to the current as the voltage is gently turned up. It would
also be interesting to look to see if there *is* any surge current when
full voltage is applied from cold.

Interestingly, I used to have great faith in EH valves, but of late,
I've found them to not be anything like as reliable as I think they were
a couple of years ago. Maybe they're getting them from a different
manufacturer now ? Do you happen to know anything about who's valves
they actually are ?

Arfa

Have you ever come across EH EL34 with suspicious inward dimples on the
dome end.? The retainers are ring and spring so probably heat-sink the
outer part of the dome , leaving the central area, which could perhaps
overheat and melt inwards. The dimples are not all the same so unlikely
an imprint from a production jig. I find it highly unlikely that 4
valves should have ended up with much the same dimple.
If the getter is activated with the valves dome down , could there have
been localised glass contact heating , causing small remelts?
All 4 test in normal range. No other signs of the valves overheating in
use, chalky print , green and black is still green and black and readable

"Phil Allison" wrote in message
...

"Arfa Daily"
"Phil Allison"

**Hi to the amp techs,

there is something odd about the HEATERS in current production EH
branded valves.

If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between
pins 4 and 5.

Check any other brand and the reading is 10 to 14 ohms.

The EH ones still draw 160mA at 12.6 volts like the others.

Similar but smaller differences exist with EL34EHs and 6V6EHs too.

That Bugera I posted about a few days back would NOT have developed
the nasty AC fuse blowing fault it did if EH brand 12AX7s were fitted -
as the start up heater current would be 3 times less.


So what's your theory ?


** I thought it was obvious.

The filament wire is not made from tungsten, as in all the others.


Well yes, that much is obvious, but if the heater current ends up at the
same as for other makes when it has reached temperature, then whatever they
do use must have a negative temperature coefficient, and I'm not sure that
any metals suitable for making a valve filament out of, do. Any theories on
what the material might be, and why they would use it over a cheap material
like sintered tungsten ?




How about hooking one of each to a variable DC bench supply, and seeing
what happens to the current as the voltage is gently turned up. It would
also be interesting to look to see if there *is* any surge current when
full voltage is applied from cold.

** Been there, done that.

12.6 volts at 160 mA = 79 ohms.



What, both of them when they have full volts on ?



Duhhh ..............


Interestingly, I used to have great faith in EH valves, but of late, I've
found them to not be anything like as reliable as I think they were a
couple of years ago. Maybe they're getting them from a different
manufacturer now ? Do you happen to know anything about who's valves they
actually are ?

** Same valves previously sold a "Sovtek " far as I know.


BTW: Ever see a " Sovtek " amplifier ?

Like the MIG100 or MIG 60.

The couple I've seen were amazing pieces of work - no PCB, laced wiring,
ceramic sockets, heavy as hell and full of MIL high parts.

Like something built for the Russian military.



... Phil

No, never seen a Sovtek amp here

Arfa

"N_Cook" wrote in message
...
On 24/08/2013 10:30, Arfa Daily wrote:


"Phil Allison" wrote in message
...

**Hi to the amp techs,

there is something odd about the HEATERS in current production EH
branded valves.

If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between
pins 4 and 5.

Check any other brand and the reading is 10 to 14 ohms.

The EH ones still draw 160mA at 12.6 volts like the others.

Similar but smaller differences exist with EL34EHs and 6V6EHs too.

That Bugera I posted about a few days back would NOT have developed
the nasty AC fuse blowing fault it did if EH brand 12AX7s were fitted
- as the start up heater current would be 3 times less.



... Phil




So what's your theory ? It seems a contradiction that the heater can
have three times the resistance, but still draw the same current ? Maybe
the material that they've made it out of has a different resistance v
temperature characteristic that decreases as the temperature increases
to get back to the same running hot resistance as other makes once they
have warmed up and their heater resistance has increased as a result,
although I'm not sure what - if any - metal has such a characteristic. I
suppose it would act a bit like the heater thermistor that we had in the
old days of valve TV sets, to stop the heaters coming up like torch
bulbs at switch on.

How about hooking one of each to a variable DC bench supply, and seeing
what happens to the current as the voltage is gently turned up. It would
also be interesting to look to see if there *is* any surge current when
full voltage is applied from cold.

Interestingly, I used to have great faith in EH valves, but of late,
I've found them to not be anything like as reliable as I think they were
a couple of years ago. Maybe they're getting them from a different
manufacturer now ? Do you happen to know anything about who's valves
they actually are ?

Arfa

Have you ever come across EH EL34 with suspicious inward dimples on the
dome end.? The retainers are ring and spring so probably heat-sink the
outer part of the dome , leaving the central area, which could perhaps
overheat and melt inwards. The dimples are not all the same so unlikely an
imprint from a production jig. I find it highly unlikely that 4 valves
should have ended up with much the same dimple.
If the getter is activated with the valves dome down , could there have
been localised glass contact heating , causing small remelts?
All 4 test in normal range. No other signs of the valves overheating in
use, chalky print , green and black is still green and black and readable


Can't say that I have, no, although I've never really taken that much
notice. I would be surprised if firing the getter would result in any kind
of glass melting. Yes, for sure, it's an intense magnesium flare, but it's
produced with such a small amount of material and is so brief that I don't
think there would be enough energy available to melt the glass.

I've just looked at a Svetlana EL34, and another Russian one whose make I am
not sure of - logo looks like a "C" inside a circle, with three short lines
sticking out of either side, each one getting longer towards the bottom of
the logo - and both of those have a dimple in the dome end. I would have
said that it was something to do with the production process of the
envelope, and it maybe varies a bit from machine to machine. Just because
four valves happen to be in the same amp - or even happen to come from the
same batch or matching set - does not necessarily mean that their component
parts were all manufactured on the same machine.

FWIW, all of the valves that I've seen over the years that have shown signs
of the glass melting and being sucked in, have shown this 'damage' in the
side wall, right over the centre of the anode, which is kinda where you
expect to see it ??

Arfa

Hi Arfa,

Sorry for the gate crashing but am I right in thinking you repair
electronics for a living and live near Northampton?

If so I have a LCD TV and a Yamaha Amp-tuner that both have PSU problems.

I have the circuit Schematics for both of them

Would you be interested in repairing these for a fee?

Whats the typical cost of a PSU repair?

Regards,,

Stephen

"Steve" wrote in message
...
Hi Arfa,

Sorry for the gate crashing but am I right in thinking you repair
electronics for a living and live near Northampton?

If so I have a LCD TV and a Yamaha Amp-tuner that both have PSU problems.

I have the circuit Schematics for both of them

Would you be interested in repairing these for a fee?

Whats the typical cost of a PSU repair?

Regards,,

Stephen


Yes, you are correct. Is it one of the big Yammy AV amps and won't power up
? If so, about 35 quid. As to the TV, depends on what make and what power
supply is fitted as to whether it is readily repairable. If it is
repairable, then anything from about 30 quid up to 60. Some power supplies
defy repair in a sensible time period or the manufacturers don't supply
detailed schematics. It is then sometimes necessary to fit a replacement,
and the cost can vary hugely. Also, some LCD faults that appear to be PSU
related are in fact on the main board, which usually renders the set BER.

Of course, I am being very general here, and it is hard to be any more than
'vague' on pricing, without seeing exactly what is what.

If you want to discuss further, just email me off-group at the address used
to post this reply.

Arfa

"Arfa Daily"


If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between
pins 4 and 5.

Check any other brand and the reading is 10 to 14 ohms.

The EH ones still draw 160mA at 12.6 volts like the others.


** What are pins 4 and 5 ??



** I thought it was obvious.

The filament wire is not made from tungsten, as in all the others.


Well yes, that much is obvious, but if the heater current ends up at the
same as for other makes when it has reached temperature, then whatever
they do use must have a negative temperature coefficient,

** FFS read my post before you reply with such nonsense !!!!!!!!!!!!!


** Been there, done that.

12.6 volts at 160 mA = 79 ohms.


What, both of them when they have full volts on ?


** What are pins 4 and 5 ??

FFS read my post before you reply with such nonsense.

The resistance goes UP from 32 to 79 ohms when power is applied.

Shakes head, over and over............


..... Phil

"Phil Allison" wrote in message
...

**Hi to the amp techs,

there is something odd about the HEATERS in current production EH branded
valves.

If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between pins
4 and 5.

Check any other brand and the reading is 10 to 14 ohms.

The EH ones still draw 160mA at 12.6 volts like the others.

Similar but smaller differences exist with EL34EHs and 6V6EHs too.

That Bugera I posted about a few days back would NOT have developed the
nasty AC fuse blowing fault it did if EH brand 12AX7s were fitted - as
the start up heater current would be 3 times less.



... Phil




I have quite a few Svetlana "Circle C" ECC83 here with 37 ohm heaters. All
others read the lower resistance range.
Except I have 2 Marshall branded ECC83, one reads high, one low, the higher
looking identical to the Circle C.

The 3 EH ECC83 I have all read high and look nothing like the Circle C.


Its possible my Circle C are fake - I bought 100 of them cheap from a
reputable supplier some years ago, and on testing a lot were too microphonic
for high gain use.
I probably ended up with 60 good ones, 25 marginal ones, and 15 downright
unuseable.
The have tall, bright silver Anodes.



Cheers,


Gareth.

"Gareth Magennis"
"Phil Allison"

**Hi to the amp techs,

there is something odd about the HEATERS in current production EH branded
valves.

If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between pins
4 and 5.

Check any other brand and the reading is 10 to 14 ohms.

The EH ones still draw 160mA at 12.6 volts like the others.

Similar but smaller differences exist with EL34EHs and 6V6EHs too.

That Bugera I posted about a few days back would NOT have developed the
nasty AC fuse blowing fault it did if EH brand 12AX7s were fitted - as
the start up heater current would be 3 times less.


I have quite a few Svetlana "Circle C" ECC83 here with 37 ohm heaters.
All others read the lower resistance range.
Except I have 2 Marshall branded ECC83, one reads high, one low, the
higher looking identical to the Circle C.

The 3 EH ECC83 I have all read high and look nothing like the Circle C.


** I have a few Sovtek branded 7025s with small, silver anodes - pulled
from an amp.

Heaters all read 32 ohms.

Despite a long search this morning, no pic of one quite the same is on the
net.

Seems incredible that Russians have found a new ( and suitable ) high
conductance heater wire to use in the last few years that is cheaper than
tungsten.



..... Phil

"Phil Allison" wrote in message
...

"Gareth Magennis"
"Phil Allison"

**Hi to the amp techs,

there is something odd about the HEATERS in current production EH
branded valves.

If you check a 12AX7EH, 12AT7EH or 12AU7EH, you get 32 ohms between
pins 4 and 5.

Check any other brand and the reading is 10 to 14 ohms.

The EH ones still draw 160mA at 12.6 volts like the others.

Similar but smaller differences exist with EL34EHs and 6V6EHs too.

That Bugera I posted about a few days back would NOT have developed
the nasty AC fuse blowing fault it did if EH brand 12AX7s were fitted -
as the start up heater current would be 3 times less.


I have quite a few Svetlana "Circle C" ECC83 here with 37 ohm heaters.
All others read the lower resistance range.
Except I have 2 Marshall branded ECC83, one reads high, one low, the
higher looking identical to the Circle C.

The 3 EH ECC83 I have all read high and look nothing like the Circle C.


** I have a few Sovtek branded 7025s with small, silver anodes - pulled
from an amp.

Heaters all read 32 ohms.

Despite a long search this morning, no pic of one quite the same is on the
net.

Seems incredible that Russians have found a new ( and suitable ) high
conductance heater wire to use in the last few years that is cheaper than
tungsten.



.... Phil




Oops, my error, the ones I have are Winged C Svetlana, not Circle C.


Here is one of them:

http://imageshack.us/photo/my-images/545/mpcx.jpg/



Gareth.