Voltage Checks

[deserat]

OK the A board had the red jumper run from IA to  OB.

+275vDC on the Power Supply Board - reads 285
+6.3vDC on the Power Supply Board - reads 6.29
IA on the A side C 4 S Board - reads 220
IA on the B side C 4 S Board - reads 220
Breg Regulator Board (both sides) - reads 220
-reg Regulator Board (both sides) - reads 0.*
Kreg Regulator Board A side  - 2.9  B side - 6

B Side regulator now biases post 20 to 145
A Side regulator still has no impact. post 30 consistantly reads 220

[Paul Birkeland]

Well, I'm glad you found the culprit.

To get things more narrowed down now, I would recommend swapping the big PC boards to see if the voltage at terminal 30 becomes adjustable with the C4S board from the other side.

This will determine whether the miswired jumper has damaged the C4S board (this would be indicated by being able to adjust the voltage at T-30 after you do this swap), or if there is still an issue on the center C4S board preventing biasing (indicated by T-30 still sitting at 220V after you swap the C4S boards).

In either case, you're getting a lot closer to having a working amp, keep at it!

-PB

[deserat]

Thanks. Should be able to do that tomorrow night.

[deserat]

Swapped the boards twice and labled them so I didn't get 'em mixed up.  30 still doesn't bias. 20 still does.

Does this indicate it's the central board? Or is there some chance that I mis-wired or the tube? The tube does light up.

[Paul Birkeland]

Yes, there's still an issue on the center board, or potentially a very hard to spot miswire in the amp. Be careful of the unused pins on the 9 pin socket on the offending side.

[deserat]

Staring at the center board everything looks to be in the right place.  Two things I'm noting.

the 2N2222A transistor on the B side of the board looks a little blacked, like burnt.  I don't recall seeing any smoke but, hey I thought I had the thing wired correctly.

Any chance you could link me to the right transistor over on digi-key or mouser? While I'm at it I think replacing the trim pots that I over snipped the leads on might make sense, may as well get it right.

I'm guessing the trim pot is one of the 2K variants of these but I don't know which:
http://www.digikey.com/products/en?keywords=%202N2222A%20transistor

Same thing here for the 2N2222A:
http://www.digikey.com/products/en?keywords=%202N2222A%20transistor

[Paul Birkeland]

The central 2N2222 is a fine choice.  You might want to ask replacement parts about getting parts directly from us, as there will be less guess work.

An acceptable substitute for the trim pot is Digikey 3299Y-202LF-ND.

-PB

[deserat]

Thanks I'm email replacementparts now. 

[deserat]

Ok. Got parts. Put them in... no affect.  It's gotten to the point where I've taken the c4s boards off so many times that the hookup wire is breaking.  Given that there appears to be no way to debug the amp beyond the stated few voltage checks,  I'm throwing in the towel and will take advantage of the repair service. Thanks for ya'lls help. It has been that kind of frustration that I consider fun.