new kaiju amp build, voltage off on last voltage check bah

[quad]

Hi

I have built one of these fine amps. This is the second build. I am at the measuring voltages on the C4S board step.

The voltages I measure are:
Board side A (voltages look good)
IA 518
OA 297
I can adjust the pot to get 175 VDC at 32U

Board side D
IA 521
OA 283 (bah)
I can adjust the pot to get 175 VDC at 46 U

Per your excellent instructions I should get OA 300 +/1 1% for OA for both boards. Clearly Board B is not in spec.

The last amp I built, I measured 300V dead on both boards for OA.

Anyway, any suggestions on this debugging this? Does this voltage difference matter - I assume it does given your tight tolerance on the voltage check for OA.

I did remove the B board and reflowed all solder connections I could. Didnt change anything.

Thank you,

Carl

 

[Paul Birkeland]

What are all the Kreg voltages on both boards?

 

[quad]

Measured Kreg voltages:

A side
Akreg: 3.63
BKreg: 6.84

D side:
AKreg: 3.53
BKreg: 9.16

 

[Paul Birkeland]

How about the "X" pad on the "B" side? (It's next to bB)

If you have 2.49V there, then you'e made it out of the voltage checks and you can blame the deviance on parts tolerance. 

 

[quad]

X pad B side 2.33

X pad A side 2.47

 

[Paul Birkeland]

Well, you have a regulator that's a little out of spec, or possibly a solder joint (likely a ground) on the board or on the 9 pin socket that isn't quite 100% (especially suspicious of the tiny resistor that grounds one grid of the 5670 and attaches to the center lug of the 5 lug strip full of the 5 zener diodes).  For the sake of collecting as much data as possible on what's going on, do these voltages move if you swap the 5670 tubes?  (I really doubt it, but it's always good to know)

 

[quad]

I had swapped the 5670 tubes earlier.

I have found an issue, hopefully it is the problem.

On both C4S boards for this kit, the RC 220 ohm resistor is missing.

I had my daughter build both of these. On the first Kaiju kit I built she built one C4S board and I built one. I had a mistake in mine, she had none
Likely when she was building it, she noted that she didnt have that resistor, but didnt tell me. And I didnt check out well her normally fine build on this boards.

Anyway it appears that I am short 2 of these 220 ohm 1/4 resistors for this RC position atm. The good news is this may fix my amp!

 

[quad]

I had parts from a 3rd kaiju amp I am building and used those and fixed another issue I found. Have 2nd amp all working now, thanks for the help! Have to finish up the 3rd amp in a bit.

I do have just a bit of ?ringing from the transformer. Not that much, but more than the 1st amp. Have the DC filament supply installed now, ringing is less when hum is less. Maybe just a normal characteristic of power transformers? Sound doesnt amplify (that is doesn't increase when volume goes up).

Carl