Hot Rod Deville crackle

[Tiny_Daddy]

This amp came in still operating on one output tube. The other output tube had a burned screen resistor and the 100-ohms filament resistors were burned open. So I replaced those tubes and resistors. Also replaced the PI plate resistors, 100K and 82K for good measure. Then I noticed the bias had drifted because the ground was erratic so added an extra ground wire to the filter caps negative. But now, if I strike a loud cord, there is a slight crackling that persists as the chord fades in volume. Then I noticed the bias had drifted up because the ground was erratic so added an extra ground wire to the filter caps negative. I have tried a different output transformer, different tubes and no feedback - it still does the same thing. The owner said this problem was there before, then after a few days he noticed the power was less (because the resistors had burned). Maybe a bad coupling cap?

[LooseChange]

\It's probably loose stuff on the board. Check all the components in the middle of the board. Especially those two 5w resistors (Are they 470r or 330r?). I'll bang on the guitar and chopstick the parts on the board. You can usually stop the crackle. A bad solder joint is the most likely suspect.

[Tiny_Daddy]

Nope, nothing loose. I can hear this, sounds more like an oscillation, even with the chassis on the bench driving a separate speaker. I don't hear it at full volume but only as the volume just begins to fade, a persistent but erratic-sounding fizzle lasting a half-second or so. Very repeatable with a loud burst from the guitar but not with a signal generator.

[LooseChange]

So the crackle is now a fizzle? Or did the crackle go away when you removed the amp from the cab?
Fizzle is usually related to tube issues.

Also, I've had out-of-cab experiences with oscillations. I have a large metal sheet that I'll ground and lay over the top of the chassis to shield it and the noises go away. Problem solved when the amp is put back in the cab. (HRD's do this too).

[Tiny_Daddy]

Fizzle/crackle, difficult to describe. Already tried different tubes. I'll check grounding and shielding, thanks.

[tcoil]

Check the solder connections on the board for the tube sockets.  I"ve had 2 hot rod deluxes (same board) that had lost a pin connection. The solder on those connections are not very strong.

[stingray_65]

Check the solder connections on the board for the tube sockets.  I"ve had 2 hot rod deluxes (same board) that had lost a pin connection. The solder on those connections are not very strong.

I have not experienced this myself, but I have heard it discussed before other places.

It seems to be a common problem, the reasoning is the socket leads are so much heavier than the other component leads. The boards are assembled and wave soldered. what proves to be sufficient heat for the small leads is not enough for the heavy socket leads and often end up with cold solder joints that last long enough to pass the warranty.

Ray

[jjasilli]

Some more info:  http://www.justinholton.com/hotrod/plateloads.html

[Willabe]

It seems to be a common problem, the reasoning is the socket leads are so much heavier than the other component leads. The boards are assembled and wave soldered. what proves to be sufficient heat for the small leads is not enough for the heavy socket leads and often end up with cold solder joints that last long enough to pass the warranty.
Ray

Same thing with any of the larger leads, like the input jacks. Even if they look good as long as your in there, hit them all.

A bad/cold solder joint on any of the jack pins could cause a crackling/fizzy sound? I've heard of stranger things causing problems.   

           Brad      

[rzenc]

I had troubles with ribbon cables... Check to see if they are ok - after some bendings they break..

The shielded signal cabling is Pretty fragile too..
Have you tried isolating the problem? Does it happen with PI tube in?
Try running a different Preamp section into it's power amp and it's preamp into another Poweramp.

Hth.
Best Regards
Rzenc