WEM Custom 15

[Murphyv310]

Hi.
I'm looking at the photo of the chassis. Did you add the X type cap to the switch? The wiring there looks suspect to me. Remove the cap as it's not in the circuit and if its a combined volume control and switch that caps location could be the issue.

[Bushbaby]

Hi
Yes, I added the snubber to the switch but I have tried bypassing the switch completely with no change to the hum. As soon as add, starting from V3, any ECC83 then the hum appears and doesn't change in volume etc.

[Murphyv310]

Thanks Rob.
OK so we know the output stage is working as it should. The things that can induce hum from V3 the phase splitter can be a leak on the valve base, an earth loop, leaky coupling capacitors C6 & C7. With V3 only in place what is the voltage on the EL84 control grids pins 3 with respect to ground -ve.
Oh and snip out that cap across the switch. Its not a snubber its for RF suppression which is irrelevant on a amp like this.

There is also the possibility that C2, 15uf is faulty a 16uf will do as a replacement.

Did you measure the resistance between pins 1 & 7 of the EZ?

[Bushbaby]

The reason I added it was to stop the huge pop in the speaker when I switch off.

[Murphyv310]

Hi Rob.
Granted it will stop the "pop" but don't fit it on the back of the switch. Caps actually can radiate hum which can be picked up by the volume control itself so we need at this time to fully eliminate everything.
Can you please check the other things as I will be off to bed soon.

[Murphyv310]

Just a little tip for you.
Use two X type caps one across each side of the switch contacts, this will effectively stop the switch off pop but will also not radiate hum as they are effectively shorted out when the amp is on so doing it that way will not radiate.

[Bushbaby]

Hi Trevor
Its OK as I will check tomorrow as I'm not at work.
Thanks again for all your help as its very much appreciated.

[Murphyv310]

No Problem Rob.
Lets hope we can sort this out for you.
Good night and don't dream about amplifiers

[Murphyv310]

Hi.
Wire the caps this way Rob

[Bushbaby]

Will do
Let's catch up tomorrow.

Best regards