Vintage Ampeg V4 Rice Crispies

[g1]

Does the crackling stop if you ground the tip of the ext.amp jack?

[The Dude]

I wouldn't necessarily go by what a cap tester says. It could still be arcing.

[Rciancia]

very good point. The crackle is indeed caused by arcing so you have a great point. Thank you.

[Rciancia]

YES IT DOES STOP !!!!!!!
The question is why I am looking at the schematic to see if I can figure it out, but your help is appreciated very much if you know the reason.

I see the suspects as

C9 (.47)
R22 (10k)
R21 (100K)
R23(10K)

??

[The Dude]

By grounding that plug/jack, you are effectively grounding signal to the grid of the second half of the DW (see external jack location on schematic). This tells you that the problem is before that. BTW, the cracked C9 you found couples signal to those jacks and the grid of the next stage, so it's certainly possible that it's the problem.

[Rciancia]

Thank you so much Dude and G1. I will wait until my .47 gets here and experiment further. I don't have any .5's either so I will wait.
I really appreciate your time pointing me in the right direction. I've learned something for sure.

Many thanks !!!
Will report progress back when parts arrive.

RON

[The Dude]

Oh, ...... excuse my poor etiquette. Welcome to the place!

[Rciancia]

One more question if I may... I have one of those HUGE Orange Drop caps .47. but rated at 400v. I am pretty sure there is 325v at this stage.. any harm in trying the Orange Drop ?

[The Dude]

There is only 325 on the plate of that stage. C9 is off of the cathode. There isn't anywhere close to 400V there, even if the tube shorted plate to cathode. A 400V cap should be just fine. You can measure the voltage there first if you doubt.

[Rciancia]

cool... doing the swap now.. will let you know...

[Rciancia]

The huge Orange Drop is in place and happy to report the Crackle is about 95% gone, so C9 was indeed a problem. You are all amazing, thank you. I do have a number of other crappy caps in this that I will replace and I suspect this will handle the other 5%. I am well on my way to success now thanks to this wonderful board and people like you. I will report back on progress until the amp is as quiet as a mouse.




Thanks guys
Ron

[The Dude]

Just a suggestion: I would tip that cap away from the tube so that the heat of the tube doesn't damage the cap.

[Rciancia]

I will replace it with the .47 630V cap when it comes in. Its a Yellow jacket and much smaller. That Orange Drop is too valuable to leave in this part of the amp

[g1]

YES IT DOES STOP !!!!!!!
The question is why I am looking at the schematic to see if I can figure it out, but your help is appreciated very much if you know the reason.

I see the suspects as

C9 (.47)
R22 (10k)
R21 (100K)
R23(10K)

??

When you shorted the C8/R16 junction to ground and the crackle remained, this proved the crackle was not before that point. If the source had been somewhere in the preamp before that point, shorting that point to ground would have killed the crackle.
When you shorted the ext.amp jack to ground and the noise disappeared, that proved the noise was not anything after the ext. amp jack.
So the problem was isolated to something between the C8/R16 junction and the ext. amp jack.
The parts you mentioned in post #19 (C9,R21,R22,R23) were all good suspects except R23 which was after the jack. Other possibilities were C8, R18,R19,R20. You had tried another 12DW7 so that was eliminated, but it would still be possible to have more than one tube show the same fault. It happens more often than we like (with tubes).

[The Dude]

No, the noise is introduced after the C8/R16 junction.

Sorry g1, I missed that part! My bad.