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Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which
I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing
just like they should, but when I apply the prods of a DVM across the
heater pins to check if they're correct WRT the switch setting, that
tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing.
Any idea WTF's going on here?
Cheers,
CD
On 3 Sep 2025 at 14:20:34 BST, "Cursitor Doom" <cd6699@notformail.com> wrote:
Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which
I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing
just like they should, but when I apply the prods of a DVM across the
heater pins to check if they're correct WRT the switch setting, that
tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing.
Any idea WTF's going on here?
Cheers,
CD
Suppose you didn't actually use a bench DVM with one input connected to mains >earth?
On 3 Sep 2025 13:56:25 GMT, Roger Hayter <roger@hayter.org> wrote:
On 3 Sep 2025 at 14:20:34 BST, "Cursitor Doom" <cd6699@notformail.com> wrote:
Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which
I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing
just like they should, but when I apply the prods of a DVM across the
heater pins to check if they're correct WRT the switch setting, that
tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing.
Any idea WTF's going on here?
Cheers,
CD
Suppose you didn't actually use a bench DVM with one input connected to mains
earth?
I'm using purely battery-powered DVMs for this project. I don't even
have a bench DVM. Perhaps I'll try a scope instead and see how it
reacts to that.
Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which
I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing
just like they should, but when I apply the prods of a DVM across the
heater pins to check if they're correct WRT the switch setting, that
tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing.
Any idea WTF's going on here?
On 03/09/2025 14:20, Cursitor Doom wrote:
Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which
I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing
just like they should, but when I apply the prods of a DVM across the
heater pins to check if they're correct WRT the switch setting, that
tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing.
Any idea WTF's going on here?
If the circuit has any sort of gain, are you creating a feedback path
with noise radiating cables that oscillates and overwhelms the power >delivery of the supply? Try the meter switched to AC, or an
oscilloscope, you may still see something.
Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which
I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing
just like they should, but when I apply the prods of a DVM across the
heater pins to check if they're correct WRT the switch setting, that
tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing.
Any idea WTF's going on here?
On 03/09/2025 14:20, Cursitor Doom wrote:
Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which
I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing
just like they should, but when I apply the prods of a DVM across the
heater pins to check if they're correct WRT the switch setting, that
tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing.
Any idea WTF's going on here?
If the circuit has any sort of gain, are you creating a feedback path
with noise radiating cables that oscillates and overwhelms the power >delivery of the supply? Try the meter switched to AC, or an
oscilloscope, you may still see something.
On 03/09/2025 14:20, Cursitor Doom wrote:
Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which
I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing
just like they should, but when I apply the prods of a DVM across the
heater pins to check if they're correct WRT the switch setting, that
tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing.
Any idea WTF's going on here?
I'm a bit confused here. You say that you set up the panels to test *a* >valve, but then you refer to the *valves* glowing like they should. Did
you test more than one valve, and did these use the same or different >sockets - eg only octal, or octal and noval? I'm also a bit surprised
that there is space to put a DVM probe on a pin when the valve is in its >socket, unless the valve is partially loose. That doesn't explain what
you found, but perhaps the socket is cracked and the pin connector is >shorting out somehow. What happens if you put a resistor (which would
draw a similar current to the valve filament) in the socket instead of
the valve, and monitor the voltage across that with the DVM?
I assume, by the way, you've seen the large number of threads here: ><https://www.vintage-radio.net/forum/showthread.php?t=201895>
Is this of any use ><https://www.vintage-radio.net/forum/attachment.php?attachmentid=246385&d=1637601490>
On 3 Sep 2025 at 15:03:52 BST, "Cursitor Doom" <cd6699@notformail.com> wrote:
On 3 Sep 2025 13:56:25 GMT, Roger Hayter <roger@hayter.org> wrote:
On 3 Sep 2025 at 14:20:34 BST, "Cursitor Doom" <cd6699@notformail.com> wrote:
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which
I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing
just like they should, but when I apply the prods of a DVM across the
heater pins to check if they're correct WRT the switch setting, that
tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing.
Any idea WTF's going on here?
Suppose you didn't actually use a bench DVM with one input connected
to mains earth?
I'm using purely battery-powered DVMs for this project. I don't even
have a bench DVM. Perhaps I'll try a scope instead and see how it
reacts to that.
On Wed, 3 Sep 2025 17:45:43 +0100, Jeff Layman <Jeff@invalid.invalid>
wrote:
On 03/09/2025 14:20, Cursitor Doom wrote:
Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which
I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing
just like they should, but when I apply the prods of a DVM across the
heater pins to check if they're correct WRT the switch setting, that
tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing.
Any idea WTF's going on here?
I'm a bit confused here. You say that you set up the panels to test *a*
valve, but then you refer to the *valves* glowing like they should. Did
you test more than one valve, and did these use the same or different
sockets - eg only octal, or octal and noval? I'm also a bit surprised
that there is space to put a DVM probe on a pin when the valve is in its
socket, unless the valve is partially loose. That doesn't explain what
you found, but perhaps the socket is cracked and the pin connector is
shorting out somehow. What happens if you put a resistor (which would
draw a similar current to the valve filament) in the socket instead of
the valve, and monitor the voltage across that with the DVM?
I assume, by the way, you've seen the large number of threads here:
<https://www.vintage-radio.net/forum/showthread.php?t=201895>
Is this of any use
<https://www.vintage-radio.net/forum/attachment.php?attachmentid=246385&d=1637601490>
Thank you, Jeff. You're a long-standing and respected contributor here
and I value your advice. These testers were made in a different age altogether and under wartime constraints. They would be totally
illegal to sell today as retail for their lack of basic safety
features. I was easily able to get prods on the valve pins by
partially unplugging the valve base adaptor. I can't recall the base
type for these valves but the test valves I used for this purpose were
all common small-signal tubes like the ECC85 and others with the same pin-outs. The issue was particularly slippery to deal with. Voltages
were intermittent (in addition to the delays due to the thermal
cut-out) and I just cannot waste any more time on it, I'm sorry to
say.
On 9/3/25 20:00, Cursitor Doom wrote:
On Wed, 3 Sep 2025 17:45:43 +0100, Jeff Layman <Jeff@invalid.invalid>
wrote:
On 03/09/2025 14:20, Cursitor Doom wrote:
Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which
I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing
just like they should, but when I apply the prods of a DVM across the
heater pins to check if they're correct WRT the switch setting, that
tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing.
Any idea WTF's going on here?
I'm a bit confused here. You say that you set up the panels to test *a*
valve, but then you refer to the *valves* glowing like they should. Did
you test more than one valve, and did these use the same or different
sockets - eg only octal, or octal and noval? I'm also a bit surprised
that there is space to put a DVM probe on a pin when the valve is in its >>> socket, unless the valve is partially loose. That doesn't explain what
you found, but perhaps the socket is cracked and the pin connector is
shorting out somehow. What happens if you put a resistor (which would
draw a similar current to the valve filament) in the socket instead of
the valve, and monitor the voltage across that with the DVM?
I assume, by the way, you've seen the large number of threads here:
<https://www.vintage-radio.net/forum/showthread.php?t=201895>
Is this of any use
<https://www.vintage-radio.net/forum/attachment.php?attachmentid=246385&d=1637601490>
Thank you, Jeff. You're a long-standing and respected contributor here
and I value your advice. These testers were made in a different age
altogether and under wartime constraints. They would be totally
illegal to sell today as retail for their lack of basic safety
features. I was easily able to get prods on the valve pins by
partially unplugging the valve base adaptor. I can't recall the base
type for these valves but the test valves I used for this purpose were
all common small-signal tubes like the ECC85 and others with the same
pin-outs. The issue was particularly slippery to deal with. Voltages
were intermittent (in addition to the delays due to the thermal
cut-out) and I just cannot waste any more time on it, I'm sorry to
say.
Seems to me it's the force of your probes on the pins of
a partways inserted tube that breaks the circuit.
Jeroen Belleman
On Wed, 3 Sep 2025 21:02:47 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 9/3/25 20:00, Cursitor Doom wrote:
On Wed, 3 Sep 2025 17:45:43 +0100, Jeff Layman <Jeff@invalid.invalid>
wrote:
On 03/09/2025 14:20, Cursitor Doom wrote:
Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which >>>>> I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a
valve, set the anode and heater voltages etc, the valves are glowing >>>>> just like they should, but when I apply the prods of a DVM across the >>>>> heater pins to check if they're correct WRT the switch setting, that >>>>> tiny extra load completely collapses the supply to the heaters! The
meter reads 0V (or close enough) and the heater glow dims to nothing. >>>>> Any idea WTF's going on here?
I'm a bit confused here. You say that you set up the panels to test *a* >>>> valve, but then you refer to the *valves* glowing like they should. Did >>>> you test more than one valve, and did these use the same or different
sockets - eg only octal, or octal and noval? I'm also a bit surprised
that there is space to put a DVM probe on a pin when the valve is in its >>>> socket, unless the valve is partially loose. That doesn't explain what >>>> you found, but perhaps the socket is cracked and the pin connector is
shorting out somehow. What happens if you put a resistor (which would
draw a similar current to the valve filament) in the socket instead of >>>> the valve, and monitor the voltage across that with the DVM?
I assume, by the way, you've seen the large number of threads here:
<https://www.vintage-radio.net/forum/showthread.php?t=201895>
Is this of any use
<https://www.vintage-radio.net/forum/attachment.php?attachmentid=246385&d=1637601490>
Thank you, Jeff. You're a long-standing and respected contributor here
and I value your advice. These testers were made in a different age
altogether and under wartime constraints. They would be totally
illegal to sell today as retail for their lack of basic safety
features. I was easily able to get prods on the valve pins by
partially unplugging the valve base adaptor. I can't recall the base
type for these valves but the test valves I used for this purpose were
all common small-signal tubes like the ECC85 and others with the same
pin-outs. The issue was particularly slippery to deal with. Voltages
were intermittent (in addition to the delays due to the thermal
cut-out) and I just cannot waste any more time on it, I'm sorry to
say.
Seems to me it's the force of your probes on the pins of
a partways inserted tube that breaks the circuit.
Jeroen Belleman
Nice theory and certainly credible. However, I get noticeable sparks
on the probe tips just on contact alone with no pressure. It's just
weird; I've never seen sparks when probing something for its voltage
level (and yes - the meter *was* set to AC volts).
On 9/3/25 23:31, Cursitor Doom wrote:
On Wed, 3 Sep 2025 21:02:47 +0200, Jeroen Belleman
<jeroen@nospam.please> wrote:
On 9/3/25 20:00, Cursitor Doom wrote:
On Wed, 3 Sep 2025 17:45:43 +0100, Jeff Layman <Jeff@invalid.invalid>
wrote:
On 03/09/2025 14:20, Cursitor Doom wrote:
Gentlemen,
I have an early AVO valve tester (twin panel type, Mk1 or Mk2) which >>>>>> I'm trying to get fully working. Anyway, I have a problem with it
which I've never encountered before. I set the panels up to test a >>>>>> valve, set the anode and heater voltages etc, the valves are glowing >>>>>> just like they should, but when I apply the prods of a DVM across the >>>>>> heater pins to check if they're correct WRT the switch setting, that >>>>>> tiny extra load completely collapses the supply to the heaters! The >>>>>> meter reads 0V (or close enough) and the heater glow dims to nothing. >>>>>> Any idea WTF's going on here?
I'm a bit confused here. You say that you set up the panels to test *a* >>>>> valve, but then you refer to the *valves* glowing like they should. Did >>>>> you test more than one valve, and did these use the same or different >>>>> sockets - eg only octal, or octal and noval? I'm also a bit surprised >>>>> that there is space to put a DVM probe on a pin when the valve is in its >>>>> socket, unless the valve is partially loose. That doesn't explain what >>>>> you found, but perhaps the socket is cracked and the pin connector is >>>>> shorting out somehow. What happens if you put a resistor (which would >>>>> draw a similar current to the valve filament) in the socket instead of >>>>> the valve, and monitor the voltage across that with the DVM?
I assume, by the way, you've seen the large number of threads here:
<https://www.vintage-radio.net/forum/showthread.php?t=201895>
Is this of any use
<https://www.vintage-radio.net/forum/attachment.php?attachmentid=246385&d=1637601490>
Thank you, Jeff. You're a long-standing and respected contributor here >>>> and I value your advice. These testers were made in a different age
altogether and under wartime constraints. They would be totally
illegal to sell today as retail for their lack of basic safety
features. I was easily able to get prods on the valve pins by
partially unplugging the valve base adaptor. I can't recall the base
type for these valves but the test valves I used for this purpose were >>>> all common small-signal tubes like the ECC85 and others with the same
pin-outs. The issue was particularly slippery to deal with. Voltages
were intermittent (in addition to the delays due to the thermal
cut-out) and I just cannot waste any more time on it, I'm sorry to
say.
Seems to me it's the force of your probes on the pins of
a partways inserted tube that breaks the circuit.
Jeroen Belleman
Nice theory and certainly credible. However, I get noticeable sparks
on the probe tips just on contact alone with no pressure. It's just
weird; I've never seen sparks when probing something for its voltage
level (and yes - the meter *was* set to AC volts).
You checked the DVM was working correctly, I suppose. Did you measure
the voltage from heater to GND? What's the cathode voltage? Are the
valves of the indirectly heated kind?
Jeroen Belleman
... I get noticeable sparks
on the probe tips just on contact alone with no pressure. It's just
weird; I've never seen sparks when probing something for its voltage
level (and yes - the meter *was* set to AC volts).
Cursitor Doom <cd6699@notformail.com> wrote:
[...]
... I get noticeable sparks
on the probe tips just on contact alone with no pressure. It's just
weird; I've never seen sparks when probing something for its voltage
level (and yes - the meter *was* set to AC volts).
Were the plugs in the 10 Amp sockets on the meter, by any chance?