Right Channel Hum

[Paul Birkeland]

OK, in your previous post you mentioned IB, OB, and KReg being 0V.  This is on the larger C4S board, not the smaller one (it doesn't have a Kreg).

IB on the larger PC board wires into the high voltage power supply at 34U, and you need to do a DC voltage check of 34U.  If it's 0V that is significant.  If it's more like 380V and IB is 0V, then they are not connected.

[thoven0215]

Apologies for the 3 year response time. I was finishing up school. After re-reading the thread and re-checking the voltages, IB and OB are at around 0.9 volts. KReg on the B side is about 0.9 volts. 34U is also at 0.9 volts. I may have not checked the lower voltage settings on my multimeter at the previous time. You said that

IB is fed from a high voltage node in the power supply.  If that node is pulled to 0V, you will burn up resistors pretty much immediately and you'll know there's a problem.  Since you haven't reported that this happened, you either do not have IB connected to the correct spot, or that wire is broken.

and on reply 12 I stated that the resistor next to the capacitor on the B side started to smoke as I checked the voltages. Could this be what you are talking about? I also used my continuity checker on my multimeter and it says that 34U and IB are connected. Thanks for your help as always.

[Paul Birkeland]

Can you post some photos of what you're seeing?

[thoven0215]

Please let me know if more pictures are needed. One of the pictures is with the amplifier powered on in order to see the LEDs. The other two are with the amplifier off.

[Paul Birkeland]

I stated that the resistor next to the capacitor on the B side started to smoke

Which resistor? Which terminals does it connect to and what's its value?

[thoven0215]

It was the 2.49k ohm 1/4 W resistor that goes into R3 on the big circuit board. I replaced it after that smoking happened along with the TL431 and the resistor measures at about 2.39k ohms right now.

[Paul Birkeland]

I think what would make sense is to put the amp back to pre-shunt regulator status and just be sure everything still works under those conditions. 

[thoven0215]

I put the amp back into pre-shunt regulator conditions, and the issue of 34U being 1.8 volts still persists.

[Paul Birkeland]

With the amp powered down and the high voltage bled off, you should be able to measure the resistor that goes to terminal 34 while it is installed in the amp, I'd imagine it will measure as infinite resistance and needs to be replaced.

[thoven0215]

You are speaking about the 130 ohm 2W metal film resistor correct? It does appear as infinite resistance. Can you please remind me what the email is to order spare parts? Thank you.

[Paul Birkeland]

replacementparts(at)bottlehead(dot)com

Typically that resistor will blow if a 2A3 is plugged into the socket without care as to where the fat pins go.  If you push hard enough, the fat pins can be forced into the skinny holes.