WEM Custom 15

[Murphyv310]

The phase splitter is V3 on the manufacturers sheet. In the meantime just insert V3 and the EZ81.
What we are doing is stage by stage fault finding. Now did you check the V3 valve base for shorts or solder splashes.

[Murphyv310]

Let us know when you are ready.

[Bushbaby]

I have checked for solder splatter, etc - nothing that I can see.
I have measure voltages of V3 with only the EZ81 and V3 in place and these are as follows, dc voltages:
Pin 1 = 240v
Pin 2 = 72.2v
Pin 3 = 80v (very slowly dropping)
Pin 4 = 0v
Pin 5 = 0v
Pin 6 = Fluctuating between 235v & 239v
PIn 7 = 70.9v
Pin 8 = 80v
pin 9 = 0v

Am I correct in thinking that the heaters are not seeing and voltage at all??

[Murphyv310]

The heaters are AC!!!!!! You can't read that when the meter is set to DC

[Bushbaby]

Hi Trevor
Of course they are what was I thinking.

Best regards

[Murphyv310]

Hi.
The voltages are just about fine. The grids are a little low but that is due to the internal resistance of your meter. The dropping of the one voltage could be due to the anode load resistor changing value, valve warming slow etc but again not a reason to induce hum.

The only other thing I can think of that is a genuine fault would be the last HT smoothing cap C2, 15uf that I have already said could be the problem. It may be open circuit or have a bad connection. Do you know how to bridge a smoother? if you do then a 4uf or above will do for a test just make sure its 250 volt working or above. If you are not sure please come back and ask for instructions.

Do the smoother first then if the same we need to see the scope on each of the V3 valve anodes.

[Bushbaby]

Back on track.
Pin 4/5 = 3.2v ac
Pin 9 = 3.2v ac

The scope pics of the anodes (pins 1 & 6) are as below. The scope probe is x1. The second and third pics are pin 1 & 6, respectively.

           

[Murphyv310]

If I am right that's a lot of ripple.
The reason for your hum.
Bridge out C2 like I've said. There is now doubt about C4 if C2 doesn't fix the issue.

[Murphyv310]

Incidentally pins 3 & 8 on V3 are bridged so both voltages should be the same.

[Bushbaby]

R E S O L V E D!!!!!!
It was C2 that was the offending CULPRIT.
I replaced the original with a new JB audio 16uF 450V 105degree electrolytic. When Trevor suggested investigating C2 I thought it couldnt be, being a new cap. I measure the ESR at 1.7R and the old one at 0.38 so decided to put the old one back. Now there is a minute amount of mains hum which I would expect to a guitar valve amp. When I put a lead in instant hum and buzzing when I put my fingers across the jack plug - when the lead was removed back to minute mains hum.
Looks like its done.
Thank you all so much indeed.

Best Regards

A very grateful Rob.