Tracing noise problem, TwinRev.

[pdf64]

Hi Pdf, well now the 100k joining from pin 6, is reading open circuit. The identical twin 100k next to it reading 140k.

The identical pair of 100k resistors on V2, are both reading 100k.

Replacing those 2 bad resistors would be a good idea

[Sea Chief]

pdf64 I just changed that pair of 100k resistors.. & bingo! I think the pop sounds fixed! 1/2w ones ok?

So now I get 297v on the pin 6's lead on the board at the 100k point. This channel's bad volume issue solved too.

Great. Now one last thing tho.. for some reason the reverb has stopped working. Just a bad buzzz when I turn up the vol getting increasingly loud, but quiet at knob minimum point.

If I could solve this.. Im all set. Thanks chaps, SC

[pdf64]

I guess the HT voltage at the other end of the resistor is really high, up near 450V?
If so, 1W anode load resistors are called for really.

Is the reverb tank properly connected, eg what’s the resistance between V4 pin 2 and the chassis?

[Sea Chief]

Shall I do a fresh thread for the reverb issue? It shouldn't be too much to fix.. I'd think.

Thanks all on this issue though- Chuck of course, nosaj & pdf64 too.

(I think a bit of vindication of my innitial bad-component hypothesis? I was determined you see!)

Very grateful chaps, Sea Chief.

[Sea Chief]

I guess the HT voltage at the other end of the resistor is really high, up near 450V?
If so, 1W anode load resistors are called for really.

Is the reverb tank properly connected, eg what’s the resistance between V4 pin 2 and the chassis?

Hi pdf, I get 1.6ohms from v4 pin 2 to chassis.

Thing is the cab & tank haven't moved a jot in weeks, so no way anything in the tank could have changed.

SC

[Sea Chief]

I swapped in another v4, switched my reverb leads around.. & reverb working again!

Great. I'll monitor the amp for a while, hopefully no pops & I can call it fixed.

Just the 1/2w 100k pair to replace with 1w. But my v2 similar pair of 100k's are 1/2w & all seems well: Any need to replace them if v2 seems ok?

Huge help chaps, thanks for sticking with me on this. (I just had this strong hunch it wasn't a conductive board!).

SC

[pdf64]

Yay!
I thought you reused the components - the 135W TR should have had 1W anode load resistors?
And if converted to TR AB763, depending on the exact circuit you’ve ended up with, preamp voltages have probably increased.
The main stress factor is probably voltage rather than power dissipation per se, but 1/2W resistors may only be rated for 350 or even 250V, whereas 1W are typically rated for 500V.

[Sea Chief]

Yay!
I thought you reused the components - the 135W TR should have had 1W anode load resistors?
And if converted to TR AB763, depending on the exact circuit you’ve ended up with, preamp voltages have probably increased.
The main stress factor is probably voltage rather than power dissipation per se, but 1/2W resistors may only be rated for 350 or even 250V, whereas 1W are typically rated for 500V.

Ah ok thanks pdf. I will order some 1w jobs & redo these 4 then.

Ive just put her back together, & the Vibrato channel is sounding much more characterful.. like this Ch1 issue was hampering it's tone.

Saying that.. I do have mild crackling still, like a fire is on in the background, & still some bad hum from the reverb: just acceptable at 3, but any higher & it it intrusively loud. And the trem has the typical bad dud dud dud ticking thing.

But no pops! Thank god for that.

[pdf64]

I suggest to replace all 1/2W anode load resistors with 1W carbon or metal film. Should be about 8, 7 x 100k and an 82k.

[Sea Chief]

I suggest to replace all 1/2W anode load resistors with 1W carbon or metal film. Should be about 8, 7 x 100k and an 82k.

Aha ok I'll search these out.

Would your thinking be, that maybe the reason the orig ones went bad, was because more voltage is possibly at this point now I revamped the circuit a bit?

I was wondering if the cap next along from my failed 100k, might have been damaged too.. hence Im still getting some noise.