Cannot Find Source of Amp Crackle

[caveing]

I had another thread on this amp- but the original topic has been solved. The problem that i'm still working on is this very annoying snap, crackle, pop and hum I'm getting in the background.

I also have weird voltages in v4- pin1 is at 266v and pin6 is at 385v... i've tried tubes. v5 ispin1=434v and pin6=236v

So far with the crackle and noise... I only get it on the vibrato channel... ie: when I have v2,v3,v4, v5 removed and just v1 and the PI installed I dont get the crackle noise. When I have the vibrato channel tubes in and v1 either pulled or in I get the crackle.

Could it be the standby switch even though I'm not getting it on the normal channel?

I've poked all around the amp, i've tested ground continuity as many places as I can think... I've removed the bright switches from circuit, cleaned pots and switches (none are scratchy like at ALL- someone replaced all the pots with CTS pots a few years before I had it I suppose) I can get some differences in hum levels when I move wires around, but nothing that stops the loud popping. When I touch pins on preamp tubes I dont get any noise (using a wooden stick) I do get noise when I make contact when measuring voltages with DMM. None of the tube sockets make noise when i move the tubes a little while the amp is on. At one point i tapped on the death cap (i do have a 3prong cord installed), and the noise stopped for a while (it does stop at times for periods occasionally- once i thought it was gone, i played for an hour straight and it didnt crackle at all) turned it on 2 hours later and it was back to rice krispies. These are loud rice krispies too.

The thing is... the amp sounds great besides this too! I'm wondering could this be the power tubes being old? I dont have an extra set of 6l6gc's at the moment to try (i do have 5881's but i dont know if i could even use them, could i?) If its a tube socket how could I tell which one it is?

Also wondering as part of additional testing- exactly what tubes can I remove from the amp and still have the vibrato channel make sound? IE: i know I can take out v1 no problem... can I take out the tremolo tube and still get sound? v4?

This thing is driving me crazzzzyyyy! Any suggestions beyond what i've done already?

Thanks so much for all the help... with your alls help this silverface pro reverb sounds FANTASTIC right now... best it's ever sounded... in fact... it's one of the best sounding blackface style fenders I've ever heard! And when the popping stops during those times it decides to be nice to me... the amp is DEAD quiet... I mean it's on the verge of breakup at 5-6 on the dial and I can barely hear a difference between positions 2 and 4 and the single pickup positons on my strat!!! It's just that quiet!!!

SO thanks amp garage! I'm prouud to be a new member and cannot wait for the days when I can contribute more!

edit:
thought someone would ask... it's biased at 60% on my 6l6gc's I think that was 40ma at 442v...

[Jana]

Why do you still have the death cap in the amp?

[Reeltarded]

Why do you still have the death cap in the amp?

Because.. .. the amp is DEAD quiet

hah I am awesome.

[tubeswell]

When I have the vibrato channel tubes in and v1 either pulled or in I get the crackle.

Could be a leaky coupling cap. Test them for DC in that channel

[Cygnus X1]

99.9% of the time I have found I missed a ground point, or it is weak when I see this problem.

Coupling cap, as said, is also good to check.
Miniscule amounts of DC can cause big headaches.

Reeltard is awesome.
But Ace is God.

[Reeltarded]

lol

Darken your room with the amp on and watch for any flashing when it crackles. Crackle sounds like tiny arcing to me. It will be fairly obvious if it is.

Remove the pilot light before you do it! Easy to see the stars in a dark sky!

[caveing]

ha! I'm gonna take out the death cap and the ground switch and all that. I am always throwing in new topics, but can anyone tell me about the negative feedback mod? Should I use a 50k linear or audio pot? and what would happen if I dont wire the 820ohm resistor in series and I let the pot go to zero resistance? Is that something I should avoid, or would that be like having no negative feedback?

I'll do the dark light check tonight!
Thanks... report back soon

[sliberty]

A bad or noisy plate resistor can cause cracking. Might try replacing the plate resistors on all preamp tubes. You could do it one at a time, but they are so cheap, maybe just change them all and see if that solves it.

[caveing]

i forgot to mention that all but like 5 components in this amp are brand new. so it kinda sucks trying to hunt down a bad component. The crackling just started randomly, not when I had replaced a component or anything.

the resistors are all measuring properly- does that mean it can still be crackling this much? none of the components make any noise when I tap on them.

could the high voltage on v4 be related?

and i didnt see any arcing with the lights out... i remember i used to see some through the crack of the amp when it wasnt tightened all the way to the cabinet- it only happened right when i turned the standby switch up- but i dont see that anymore.

My number 1 suspect is the .0033uf and the 500pf reverb coupling caps. bvut i dont have extras of those values at the moment

[sliberty]

They can measure properly and still crackle. Based upon your testing, it would appear that there is no need to replace the plate resistors on V1.

Another possibility is a bad solder joint. Reflow solder on all solder connections. If there is a lot of flux on them, clean them and reflow.

[Reeltarded]

Really? The standby switch used to arc?

BYPASS IT! That can be a pretty common cause of crackling, popping, sputtering and such.

Anything that used to arc and doesn't now has new paths somewhere to ground as likely as not, all made of evil carbon.

[caveing]

Really? The standby switch used to arc?

BYPASS IT! That can be a pretty common cause of crackling, popping, sputtering and such.

Anything that used to arc and doesn't now has new paths somewhere to ground as likely as not, all made of evil carbon.

i never said i knew it was the standby switch... i said that i believe i used to see a flash of light when i turned the amp on... it wasnt near the standby switch it was more on the board. it really could have been the pilot light now that i think about it, but im not sure

[abelljo]

A bad or noisy plate resistor can cause cracking. Might try replacing the plate resistors on all preamp tubes. You could do it one at a time, but they are so cheap, maybe just change them all and see if that solves it.

I always change old carbon comp PL resistors with new metal film 1 watt. Old Fender that are noise tend to get a lot better when I for this, unless the arching is somewhere else as could be the case with paper bobbin transformers. Either way old carbon comp caps absorb humidity, they sound good, but not sure it makes a big difference here. I would just swap with metal film.

[Milkmansound]

Are you using switchcraft input jacks?

[Phil_S]

I had another thread on this amp- but the original topic has been solved. The problem that i'm still working on is this very annoying snap, crackle, pop and hum I'm getting in the background.

Lot's good advice being given, so I'll just put in mt 2¢ on diagnosis. I'd go for plate load resistors on the snap crackle pop. IMO, the hum is separate from that.