Custom Vibrolux Reverb RI vibrato issues

[rockman627]

Original issue was excessive hum. I changed the filter caps and wondered if changing C37 was necessary. There was still hum and I had the cap so I did. When I tested the amp, it would develop a steady thump after about 20 minutes. Similar to a vibrato tick but a deep tone. Complicating matters is the boss had me install the Moyer mods a year ago. At the time of completion, everything worked.
Sometimes I turn the amp on and there is no thump. The next time I turn it on, it's back. If I turn the intensity on full, the thumping stops until I turn it back down. The first time I tested the amp, the vibrato worked even with the thumping, but now it never works. Reverb does work however.

Here are some readings
A.C. in 119.5 vac
B+ 422 vdc
Z. 422 vdc
Y. 348 vdc
X 294 vdc

V8 3. 419V 4. 421v 5. -39v
V7 3. 420V 4. 421v 5. -39v
V6 1. 259V 2. 15V 3. 23v 6. 252v 7. 16V 8. 23v
V5 401v 0V 0V 420V 400V 23v
V4. 210V. 0V. 01v 421v. 400V 0V
V3 420V 0V. 03v 419V 0V. 03v
V2 195V. 0V. 01v. 182v 0v. 01v
V1. 196V. 0V. 01v. 160V. 0V. 01v

I hope this is intelligible. I got tired of fighting the auto correct.
Fender-Custom-Vibrolux-Reverb-Reissue-Schematic.pdf
Custom_Vibrolux_Reverb_Moyer_Mods.pdf

Well I can see my neat columns did not translate. From V6 to V1 it is always pins 1,2,3,6,7,8.

[Helmholtz]

Does the thumping change with the tremolo frequency?

Are both output tubes idling at (almost) same currents?

[rockman627]

Ok I'm at my bench. V7 was 39mv V8 was 36mv. My bias probe converts to mv.
At first the thumping changed. It stayed the same speed but went from thump to thu-thump. A little later it went back to a single thump that followed the frequency of the speed knob.
I noticed when there was thumping, V7 would be around 180mv, and V8 would be around 25mv. Those readings would fluctuate a little.
Right now the thumping has stopped.

[Helmholtz]

Right now the thumping has stopped.

Does the tremolo still work?

[rockman627]

No.

[Chuck H]

Have you replaced C37? Have you tried a known working tube in V5?

Power tubes seem biased a little hot at the moment.

[rockman627]

Yes I ended up changing C37 just to try remove the remaining hum. Since the problem is kind of intermittent, I fear that what I have to do is remove the pcb and check the solder connections. This amp has wires going from the pots pcb to the mainboard and it is really delicate. I broke quite a few connections and had to do some hard wiring.

[rockman627]

OK this amp is rarely ever rented so it sat for a awhile as more popular amps needed attention. Eventually I removed the PCB, touched up the solder joints, fixed the wires I again disconnected, and put it back together. I turn it on and wow, no problems. Reverb works no noise, and vibrato is working.. But after about 10 minutes, the sound gets thin and tinny, and the bass and treble pots have no effect when you turn them. This only happens on the bright/vibrato channel. I'm thinking R17 stops signal from going to the treble and bass pots. Any other possibilities?

[rockman627]

Ok everything is quiet now, so I'm getting back to this. This thread helps to remind me where I am in this situation. Excellent!

[g1]

Check R19 and it's connections.

[rockman627]

R19 is close. After repeatedly studying the schematic to determine the signal flow, I couldn't figure out how signal was not going through the bass and treble pots but still got to the volume pot. I had given up and decided to double check all connections in the bright channel. It turns out there was no connection between V2 01 and R17. Back when I did the Moyer mods I had to hardwire a broken connection from the main board to the daughter board and the pad slightly lifted which is why it was intermittent. So I did another hardwire from the broken pad to R17 and everything is good now. Consider this closed and thanks again everyone.