Staticy Woosh when turning off standby, background grit: Rivera Fandango 55

[Enoch0)))]

I'm re-tubing a Rivera Fandango 55 for a friend. He complained of it not "sounding right" and not clean when it should be clean. I immediately thought it was tired tubes, so we ordered a set of new production Mullards (both 12ax7s and EL34's) and a JAN/GE 5751 for V1 to tame the gain a bit.

There is a definite grit/sparse static in the background when playing a note. If you're not playing, there's no sparse static. As soon as you pluck a string, the static/popping comes back and fades off as the note fades off. It's not extremely loud, some people might not even notice unless someone mentioned it, but it's definitely there. Additionally, when switching the amp off off standby (to fully on), it makes a ~1.5 second reverby Woosh/static sound that almost sounds like you gave the reverb tank a hard wack.

Well, I popped the new tubes in and the issue is still there. I've admittedly not re-biased the amp yet, but I doubt the bias would be the culprit, since it existed with the old tubes. I suppose the bias could be off for both sets of tubes. There is no apparent redplating or arcing of any sort.

I should mention that I was also asked to repair a loose input jack from a forward fall with the cord plugged in which bent the input jack a bit. I pulled out the input jack board, and tweaked everything back into place, and seems to be back to normal. I can't imagine a shorted or open jack would cause such symptoms though.

Could caps of some sort cause this issue? Any other ideas?

Thanks!

[Enoch0)))]

I just pulled the PI. The whoosh/static upon coming off standby isn't there anymore. Does that mean it's an issue with something before the power section?

[Enzo]

It would seem so, at least.

[Enoch0)))]

I've tried disconnecting the reverb tank, no change. I've replaced each tube position with a known good tube one by one, no change.

Oh, I should add this amp has had the apparently popular boost amt adjust mods done. There has been two knobs added to the back which each control the boost amount for their respective channel. The job seems well done, but I'm admittedly not particularly that familiar with this particular mod.

Maybe the next step should be poking around to look for loose/microphonic components?

[Enzo]

No, the next thing to do is start a systematic search for the problem. Isolate the problem.

You pulled the PI tube and it stopped your whooshing, so THAT is coming from either before the PI or right at it. But a whoosh may or may not be related to distortion on played notes.

I'd see if all channels are affected or just one. I'd check the voltages on all tubes to see if any are out of bounds. I'd look for unwanted DC offset, indicative of a leaky coupling cap.

[Enoch0)))]

Well, I broke down and brought the amp to a friend of mine who's worked on tube amps for 30+ years (like you, I'm sure, Enzo). He told me the problem is there is no problem. ha! Said the woosh is probably just from the tube driven reverb tank getting a surge of "juice" when coming off standby. Also the background grit didn't exist when he plugged in a single coil strat. May have been the particularly high gain humbuckers in the LesPaul I was using. (Dimarzio Super Distortion). He gave it a clean bill of health, so I must have just been a bit too paranoid/OCD about what I was hearing. I greatly appreciate the help Enzo. As usual, you're an amazing resource. Cheers!

[daz]

I've had that exact symptom a number of times while making many tweaks to a amp and it's always been a bad solder joint usually on a plate resistor or coupling cap. Especially common when i'd be tweaking a lot and swapping many values in a certain spot and the solder got dirty and old. But in any case i've had that many times usually in that same place....plate R or coupler.

[R.G.]

I like the solder joint as a culprit. Could be a socket with a bad contact too.

Remelt all the solder joints.

If it still does it, clean and retension the tube socket contacts.

If it still does it, scope it and look for a burst of RF oscillation as it comes up. In fact, that wouldn't be a bad thing to do while you're messing with solder joints and tube sockets. Could be bum bypass caps letting it scream in the AM band.

[Enoch0)))]

I'll poke around a bit and see what I kind find. This amp is quite "busy" inside. Remelting everything would take quite a while I'd imagine, and require removal of quite a few of the various boards. This thing is zip-tied and glued all over the place so the job would be quite a pain.

I did notice the slight crackle over cleans was reduced almost nothing when using a strat in comparison to my Dimarzio Super Distortion equipped Les Paul.

Again, both of these issues are very quiet. If you have the master past 1.5 you can't hear them at all. So the consensus from you guys seems to be that the "woosh" isn't "normal-ish"?