Voltages off. Causing volume imbalance?

[Bottle Rocket]

The following voltages are off:

Terminal
6 - starting around 125, then decreasing to below 100
C3 - 1.118
C7 - 98
C9 - 98

I tried resoldering in numerous places that connect to those terminals, but haven't gotten any changes in my readings. I'm wondering if this could cause long term damage and I think this is causing a volume imbalance between my left and right channels. Would this do that?

Also any ideas on what's causing this and what could be a fix?

Michael

[Bottle Rocket]

The right channel is definitely muted. I'm playing the Beepree through Paramount 300b's. Both Paramount monoblocks have correct volatages.

I've resoldered all terminal joints and some of the pc board connections on c socket side. Still no changes in the above volatage readings. All the other volatages remain in normal range.

Wondering if a capacitor is on the fritz or something else altogether?

[Rocketman248]

Have you tried swapping tubes?

[Bottle Rocket]

Yep, swapped both sets of tubes and the low voltages, low volume remain for the right channel.

[Paul Birkeland]

Any piece of kit that hasn't passed its voltage checks should be considered to not be working and should never be used in a system until the issues are resolved.


Can you check the R1 resistor values on the C side large C4S board?  If they were backwards, this issue could arise.

If they are correct, temporarily run the amp without the 300B on that side and recheck the voltages at that C socket.

-PB

[Paul Joppa]

If PB's test fails (you have the right R1s in the right places), then here's another possibility:

C3 connects to kreg on the PSU board. On the opposite edge of that board, there is a 2.49K resistor, one end of which is grounded. I suspect that resistor is not connected. To check, measure the resistance to ground of each end of the resistor - one end should be near zero, and the other end near 2490 ohms (2.49K). Make sure the 2.49K end is properly soldered.

[Bottle Rocket]

Looks like both R1 resistors are on the correct sides. I also checked the 2.49K resistor on the PSU board and it is in the right direction. I resoldered the connections to make sure it's connected. The initial voltages unfortunately remained the same.

I then removed the 300b tube on the C side and the voltages are as follows:

Terminal 6 - 185
C3 - 1.94
C7 - 185
C9 - 172

[Paul Joppa]

Then one of the pins on the 431 regulator is not soldered, or perhaps the 431 is dead. My two cents, but it's late in the evening, so big grain of salt time!

[Paul Birkeland]

Yes, I also vote that either the 431 is in backwards on one side, or maybe a PN2907 is installed in its place.

[Bottle Rocket]

Great call guys! The 431 regulator and PN2907 were switched. However the 431 broke when I was removing it so I'll have to order a new one before I can check and see if things test within normal ranges.

Thanks for the help in identifying the likely culprit.

[Paul Birkeland]

I'm glad you found the issue.  You're not the first, and certainly not the last to mix these up!  In my own parts bins, the TL431's and another visually similar transistor (2N3904 I think) occupy adjacent compartments.  I know that if I see about 35V at Kreg in a project that I've stuck a 2N3904 in there by accident.