• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

PYE Stereo Black Box G63

I'm part way through restoring a Pye G63 and progress has been good so far with all dodgy caps and over tolerance resistors replaced - this includes all electrolytics.

Although the stereogram powers up ok with the usual but acceptable background hum I only have one channel working!

This is my first foray into push-pull, phase splitter valve technology i.e. two pairs of matched ECL82s, so not sure where to start with fault finding for the missing channel?

I am more comfortable dealing with super het radios where the signal path is much more straightforward and linear. I have the standard range of test equipment - DMM, oscilloscope, function generator, signal injector etc. I also have the Pye G63 service sheet with full schematic.

Any help or assistance to get me started would be appreciated.
Hi Donald! I'll give your thread a nudge.

I recently lost one channel of my Rogers HG88 MKIII integrated valve amplifier and discovered that it was simply that the anode resistor of the input triode had gone open circuit.

So, it's worth getting the ohmmeter out and checking all those resistors again!

However, for expert opinion, are you able to post the schematic of the amplifier?
I've attached a typical ECL82 PP amplifier circuit to be getting on with!


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    ECL82 Push Pull.gif
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the stereogram powers up ok with the usual but acceptable background hum ... I only have one channel working!

The hum would indicate that the power amp section is OK and that the fault probably lies in the preamp section.

Perhaps rather obvious, but the ECC83 could be bad, so you could try a substitute.

The ECC83 section may not be receiving power so check the series dropping resistor in the bypass network leading to its anode, as well as checking/substituting the associated bypass capacitor. I know you've already replaced resistors and dodgy caps, so perhaps you need to look for a bad solder joint?

That's about the limit of my meagre knowledge, so hopefully an expert will chime in. You could try injecting a signal at the input to the phase splitter to confirm that the power amp stage is working.

P.S. And, of course, my schematic shows the typical voltages you should be finding at various points in the circuit.
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Thanks Galu that's really helpful.

I've attached the schematic for part of the Pye G63 right hand channel and as you can see there are several components between the PU input and the volume control (R3):-


All these will be checked again but I can't get access to the stereogram until Friday of this week so no hurry.

I'm assuming that '... the series dropping resistor in the bypass network leading to its anode ...' is R4 in my schematic while the ' ... the associated bypass capacitor ... ' would be C3?

I thought about injecting a signal as you suggest but wasn't sure exactly where the 'the input to the phase splitter' was on the schematic?
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We're talking R7 as the series dropping resistor. C5 and C6 should be checked in association with R7.

R4 is the anode resistor similar to the one that went open circuit in my amp.

The input to the phase splitter is the grid of V3A fed by the wiper of R10.

(To be clear: V1A is the pre-amp, V2A & V3A form the phase splitter, while V2B & V3B form the PP ouput stage.)


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I suspect these components are for pickup equalisation.
They are a "Loudness" network. And very unlikely to be no-sound.

I only have one channel working!
So compare to the working channel.

Also: all the grids are at DC ground. A finger (preferably a metal stick for precision poking) on each grid should produce "bZZZZT!" in proportion to how far along it is. One grid bzzzz1 and the one before silent, your trouble is between.

While pin 2 grid is groundy, pin 1 can give a "zing" across a finger to chassis, and worst-case a serious shock through the chest (work one-handed).

A faulty track on a volume control
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Maybe DIYaudio should include one of those smiley-face Like options, for good hearted funnys. PRR seems to earn more than his required share.

Always clean all the pots and switches in the signal path first. If that doesn't work, you may need to do it again. In America, the juice of choice is called Caig DeOxit D5, and there's a Fentanyl-level version D100. Spray (if you're lucky and the part has a big enough opening) or weep (if not that lucky) some cleaner down onto contact surfaces. Operate them vigorously, distributing juice. Repeat as needed. Never use WD40 or other petroleum-based sprays.

All good fortune,
The Pye stereogram is at a friend's place so I'm not going to be able to test using my signal generator and 'scope.

Best I can do is to take my Velleman signal tracer/injector and DMM which are just two tools from my arsenal that I use for testing vintage valve radios.

The Velleman injects a tone that can be heard at the speaker assuming all is well and I normally start at the wiper of the volume control.

Looking again at the schematic in Post #7 above can, I use my Velleman in a similar way on the wiper of R3 and then progressing through the circuit to Pin 2 of V1A, the wipers of R6, R8 and R10 to Pin 1 of V3A - or is that too simplistic an approach?

In Post #11 above Chris mentioned Caig DeOxit D5 but I tend to use Fader F5 for potentiometers which has given me better results - just my opinion and don't want to start a D5 vs F5 war!
Some good progress today in terms of narrowing down where the problem lies but sadly no resolution!

First point is to correct my own Post #7 above and clarify that I am actually missing the Left-Hand Channel.


Using my Velleman signal tracer/injector on the sliders of the ganged volume control I am getting a loud beep on the Right-Hand Channel (R3) but a very, very faint beep on the Left-Hand channel (R30).

Checked the pin voltages for the ECC83 and they are compatible with those shown on the service sheet although a little high as I am using a DMM not an Avometer.

PYE G63 – ECC83 Pin Voltages
Pin 1
Pin 3
Pin 6
Pin 8
Service Sheet
V1 A/B

So this tends to confirm that the problem may lie in the output stages and not the pre-amp stage or the controls?

Moving on to the output stages and I carefully measured all the pin voltages for the ECL82s :-

PYE G63 – ECL82 Pin Voltages
Pin 2
Pin 6
Pin 7
Pin 8
Pin 9
Service Sheet
V2 A/B
V3 A/B
V4 A/B
V5 A/B

Once again most readings are bit high as I am using a DMM but we have a clear issue at Pin 8 and Pin 9 of V5A!

Swapped over V4 and V5 just to test the valves but the outcome remained the same - the problem still lies with V5A with Pin 8 being the cathode and Pin 9 the anode.

First question is whether or not the high voltages above would lead to the loss of the Left-Hand channel and poor response at the slider of the volume control R30?

I had a quick check on the components associated with V5A but nothing seemed untoward - I will check again of course but not sure which ones would cause this problem. As I said in my OP 'This is my first foray into push-pull, phase splitter valve technology ...'. I think I've found the location of the fault but not sure about its cause so any help would be appreciated.
Thanks Chris for your ongoing support - the pin voltages for the output pentode section of V5 i.e. V5B seem ok so it's just the triode section i.e. V5A where we have a problem?

I'll recheck all my solder joints and measure R37, R38 and R39 again. Both C22and C25 (electrolytic) will also be checked.

Anything else I need to check?