Koch Twintone I - issue in power section

[Tone Meister]

The website froze for me about the time g-one was helping me sort this out yesterday. I will be unable to respond to this thread until later today, but I do welcome in advance any troubleshooting suggestions that anyone offers.

[g1]

Check for bad solder or open resistor at R60,61,&62.
Try your cap to ground on either side of R60, what happens?

[Tone Meister]

I won't be able to get back to this amp until tomorrow. Had some unexpected shows come up this week. I'll look closely at R60, R61, and R62 first thing.

Thanks g-one.

[Tone Meister]

OK, bear with me here. I tested R60, R61, R62, and R63 and used the cap to shunt the circuit in several places.

R60 (100K) = 98K
R61 (470K) = 481K
R62 (10K) = 8.6K
R63 (47K) = 46.3K

When I use the cap to shunt R60 at the junction of pin 7 of V4, the noise goes away leaving a bit of hum, but the noise remains when shunting the other side of R60. Likewise, on the V4 pin 7 side of R61 the noise remains. When I shunt between R61 and R62 the noise goes away leaving the same small hum. When I shunt between R62 and R63 then a very different noise occurs (exactly 60 Hz measured with my Fluke at the speaker jack)

[g1]

Lift one end of R63, does the noise go away?
Did this problem just start one day? Was the OT replaced or were the power tube sockets rewired?

[Tone Meister]

Lift one end of R63, does the noise go away?
Did this problem just start one day? Was the OT replaced or were the power tube sockets rewired?

(Answering from my phone)
The problem started as an annoying hum and lasted several shows that way. Then one day in the studio it increased to the point that the amp was unusable. The OT and all tube sockets are stock.

The rub is this: I removed the PCB to inspect the solder side and it is a major PITA to reinstall it. I am not in front of the amp right now, but I plan to: 1) meter that part of the circuit for continuity, 2) replace R60, R61, 3) examine all tube sockets and re-solder every pin

[g1]

If you are going to go ahead and replace R60 and R61, seeing as the board is a pain, also replace R62 and R63, and C40.
BUT, before any of that, clip one end of R63 and see what happens. This will greatly help further diagnostics.

[Tone Meister]

I should have been more clear in my previous post. I had already taken the PCB board out of the chassis yesterday before being called away. I'm back on it this morning, so I reckon I will go ahead and replace R60-R63 and C40 and leave R63 lifted and reinstall the board. That means I'll have to re-pull the board to solder R63 back in at some point. <sigh>

[Tone Meister]

Waiting on a couple of parts ...

[Hotlicks]

Ancient thread, but... I have the same issue with my Twintone 1. Did this ever get solved?