Right channel hum and no signal

[Sp33ls]

Okay, I could see that. The only real difference I saw between the two was that the "initial accuracy" was 2% for ACZ and 1% for BCZ. 

I sent Mouser an email to see if they could swap it to ACZ just to be certain there won't be any issues. I also picked up a few extra transistors and diodes just to have as backup.

Does the LM431 protect the capacitors from hitting their voltage limits?

Thanks again!

 

[Paul Birkeland]

No, the LM431 regulates the high voltage to 150V.

 

[Sp33ls]

So, I swapped out the LM431 and plugged everything (including all the tubes) back in to see.

Still having the issue. But, I've noticed something interesting.

When I first turn on the amp (cold start), the voltages actually appear to be closer to normal (150V & like 2.5V), but then after several seconds, they both just take a sudden dip. What could cause behavior like that... a capacitor?

 

[Paul Birkeland]

Pull the 6AQ5s and look at your Kreg voltages again, as well as the "X" voltage.

 

[Sp33ls]

With or without the white lead from the 6AQ5 plugged in to Kreg?

 

[Paul Birkeland]

The white lead can be connected.

 

[Sp33ls]

KregA: 0.4
KregB: 1.38

60 VDC & 1 VDC on A side.

214 & 2.18VDC on B side.

 

[Paul Birkeland]

How about OA on the high current board on the bad side?

 

[Sp33ls]

It was around 50VDC... oscillating a bit upwards.

 

[Paul Birkeland]

With the 6AQ5 pulled out? (And the 6080 should be pulled out, but 12AU7 in) This is a bit of a tough one to debug since you said the amp was previously working.  Low voltage on OA on the C4S board tends to point to a miswire or short downstream of that board.

 

[Sp33ls]

Oh, sorry, that was with the 6080 still plugged in.
Only 12AU7:

X: 226 & 1.9
KregA: 1.1
KregB:1.44
IA: 227
OA: 226

 

[Paul Birkeland]

Now try the 12AU7 and 6AQ5s with no 6080.

 

[Sp33ls]

12AU7 and 6AQ5s with no 6080.

X: 150& 2.5 (163 & 2.5 on B side)
KregA: 7.8
KregB:1.95

High curent:
IA: 215
OA: 150

 

[Paul Birkeland]

Would you be able to swap the 6AQ5s from side to side to see if the low KregB voltage follows a tube? 

Seeing 7.8V at KregA makes me very, very suspicious that you have the R1 resistors swapped on the high current C4S board.

 

[Sp33ls]

Swapping the 6AQ5s from side to side does not change much.

One interesting thing tho, is that the reading on KregA starts at around 9.2 and then gradually decreases in voltage at a rate of about .01VDC every few seconds. That gradual shift in voltage seems to be a common behavior I'm experiencing in a few spots. I'm just not sure what would cause a shift in voltage over time like that...  ???

Since the left channel appeared to be working fine, would that rule out the power supply as being the culprit? Just wondering if part of the power supply is separately responsible for each channel.

 

[Paul Birkeland]

A loose resistor on the 6AQ5 socket could do that.

 

[Sp33ls]

Hmm.. none of them seem to be loose.

So, with the  6080 inserted, the two LEDs on the B side of offending high current board light up (next to the capacitor). The other two on the A side don't light up at all.

Without the 6080, the B side doesn't light up (this might be normal, though?).

 

[Paul Birkeland]

The LEDs lighting up or not lighting up aren't really informative in and of themselves, but your voltages are.

The difference in Kreg voltages when no 6080 is installed does suggest an issue with the build.  This could be R1 resistors that are switched accidentally, or a miswire.  I would be paying very, very close attention to the 6AQ5 sockets.

 

[Sp33ls]

The R1 resistors look to be fine. I'm guessing I probably would've noticed issues earlier, tho, since my kit was working fine for about a year, right?

This issue really only appeared after removing the bell end for the transformer to paint it. Not right after, tho. There was a small period of time where everything was fine. I did touch up some joints during this time tho... Mostly around the power supply.

I'm curious if you have any spots I can measure with the power supply and high current board in order to help trace down where the issue might like.  I don't see any issues with it when scanning for bad joints, and I don't recall unwiring anything.

 

[Paul Birkeland]

I've suggested the spots several times in this thread.  When you took the amp apart to paint the transformer, you may have jostled a connection that wasn't solid, and hence these issues cropped up.