High voltage checks - help please!

[OutFishing2]

Thanks Paul, really appreciate your patience working this through with me.

The wires are definitely in the right places. It's a funny one. Is there any chance it could be the vregs, or the 6aq5s or dudes at Q1 and Q2?

I'm sure it's not the 6aq5s since switching them over makes no difference. Would switching the Q's from A to B reveal anything?

 

[Paul Birkeland]

You have higher regulated voltages than we would expect with adequate Kreg voltages at each 431 regulator to allow them to do the regulating they would normally do, but yet nothing is happening with them.  Having this happen on both sides would suggest a build issue rather than a component issue.  Were any parts substituted by chance?  You could certainly try replacing the 431 regulators, but they aren't behaving like failed 431s.

 

[OutFishing2]

Alternative 431s arrive on Wednesday so I'll have a go with them.

6AQ5s arrived today and made no difference to voltages but that was expected. Fascination anticipated with future tube rolling.

I used the BH parts except in two areas.

The 0.1uF caps on the low current board are mundorf. I substituted the stock dayton's in/out during this troubleshooting. It made no difference to voltages.

The four tube sockets are from a local firm. Ceramic gold plated. Described as B9A, B7G and octal sockets. I've since read a thread here where you advise against substituting sockets as they can give trouble so I'm readying to switch those over to stock.

 

[Paul Birkeland]

If you swapped in ceramic sockets that are about the same as what we provided, just leave them in there.  The teflon ones and some of the other exotic types can cause some real problems though. 

If you do completely remove and replace all the sockets, I would expect more problems to pop up, so definitely don't do that.

 

[OutFishing2]

Great news. The new 431s are in and the voltages immediately went to spec. 4.6v on both kreg and 149v on the IA and IBs.

Quite how you narrowed the fault down to the two vregs from the other side of the Atlantic is something I will take a long time to understand. Thank you!

 

[Paul Birkeland]

something I will take a long time to understand.

You and me both!  I'm glad you got it nailed down. 

 

[OutFishing2]

Thank you. The C2A really is a superb amp. I am extremely impressed at how well it sounds as a preamp as well as with headphones. Rock solid performance. The stepped attenuator went in today and it's all working beautifully. Thanks again.