A background crackling sound coming from my tube amp?

P

Petros

New member
Amp is a Rivera Pubster 25. It's been fine for many years, until now. The noise is an intermittent crackling sound, not very loud, but you can hear it. It gets louder as you turn up the volume. Stops when master volume is all the way down. It sounds a bit like when a cable has a short in it. It starts as soon as the amp warms up, and it makes the noise with and without the guitar plugged in. It's not triggered by a note being played. It happens at random and lasts for a few seconds, stops, then comes back. It is not the following:

Preamp tubes - I swapped these with new tubes and it made no difference

guitar cable - no defect as can be heard direct-in though my audio interface

combo speaker and cable - Swapped this with another speaker and cable and still heard the noise.

Power cable and outlet - I tried to plug the amp into several electrical outlets in case the power supply is causing it. Still there.

I don't have another set of output tubes to check. These are a pair of Electro-Harmonix 6V6s. All I could do was pull them out and re-seat them to make sure the connections are tight. I also swapped them and it made no difference. I have never changed these, and I've had the amp for 8 years. I didn't suspect tube wear because the amp is only on for a couple hours maybe three times a week and at a modest volume. The amp didn't fall or take a hard knock. The only other problem I've had with this amp is the volume pots were getting scratchy, but it went away after I exercised the controls back and forth about 20 times. Do you think the likely issue is the output tubes?
 
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Re: A background crackling sound coming from my tube amp?

Found this at the Soldano website:

"If you’re hearing strange sounds coming from your amplifier, turn your gain section up in volume, and slowly turn the master volume down. If the noises persist after the master volume has been turned down, it’s an output tube. If the noises go away after turning the master volume down, it’s an input tube." http://www.soldano.com/amp-help/guitar-amplifier-tube-maintenance/

--But this suggests it's a pre-amp tube. I replaced these with new tubes and it made no difference.
 
Re: A background crackling sound coming from my tube amp?

One trick I have heard to try to eliminate noise is to use electronic contact cleaner on the tube pins, and to seat and re-seat the tube a few times to clean the tube socket and make sure you get a clean contact from the tube socket to the tube pins.
 
Re: A background crackling sound coming from my tube amp?

I think I've got the problem isolated to the preamp section of the amp. When I plug the guitar into the "power amp in" jack (Rivera's name for the effects loop input), which makes the signal go straight to the power amp section, I can hear the guitar through the amp fine and the background crackling noise goes away. That would eliminate the output tubes as the problem. When I plug the guitar into the "Preamp out" of the effects loop, the noise is still there. Only thing is, I still don't know what's wrong because I've tried 4 different preamp tubes that were all working fine last time I installed them and the noise is still there.
 
Re: A background crackling sound coming from my tube amp?

Bad solder joint. Or one of your preamp resistors is going bad. Or dirty input jack that has some crap between the shorting part of the jack where it meets the ground. Does it go away when you plug into that input jack?
 
Re: A background crackling sound coming from my tube amp?

Scott_F said:
Bad solder joint. Or one of your preamp resistors is going bad. Or dirty input jack that has some crap between the shorting part of the jack where it meets the ground. Does it go away when you plug into that input jack?
Click to expand...

When the guitar is plugged into the front input jack, the noise does not go away. The crackling background noise is there with or without the guitar plugged in, and only stops when the guitar is plugged into the "power amp in" for the effects loop.

I'm finding it hard to believe Rivera would make an amp with a bad solder joint and only now after 8 years has this defect surfaced. I had a look inside the 1/4 opening of all the input and output jacks with a flashlight and I see no dust inside.

I have already been told it might be a resistor in the preamp section for the grid or plate voltage. I can't really troubleshoot something like that.
 
Re: A background crackling sound coming from my tube amp?

First I will say that Scott F is probably right...or at least that would be where I looked first (at this point)

As to Rivera quality....it can be a real small thing that is exacerbated over time. Current and heat from the tube(s) can exploit a very marginal pin hole, or piece of crud from day one. I would not think anything less of Rivera if that were the case.

But first I would clean and/or re-tension preamp tube sockets, and take a shot at the plate resistor(s).
You can look for the start of the dirty signal with a simple audio probe...but that is probably beyond your experience.
It may be tech time for you unfortunately.
Do you live near me.?
best
 
Re: A background crackling sound coming from my tube amp?

Had that problem in a Boogie 50/50. I had a variable bias installed and let them do a recap at the same sitting and the problem was gone. That amp was 15 years old at the time though.
 
Re: A background crackling sound coming from my tube amp?

Thanks for the responses, guys. I'm waiting on Rivera with an email. If it looks like it's not the tubes (and that's what it looks like) I might remove the chassis from the combo amp and bundle it up to ship to them. I'm trying to find out what Rivera will charge to take a look at it. I'm in New Mexico.
 
Re: A background crackling sound coming from my tube amp?

I am not sure how easy (or hard) it is to get at the tube sockets in that amp...but if you are going to yank the chassis for shipping, you may want to take a shot at cleaning the sockets.
Any brand of electronics cleaner will work...preferably without lube in it. Just soak the pins, and work the tube in and out several times.
Even alcohol is better than nothing.
It MIGHT save you the Hassle/Expense of shipping to Rivera.
best
 
Re: A background crackling sound coming from my tube amp?

I've seen crazy things. Bad solder joint or a speaker jack getting a bit loose and not being grounded properly. Can be a bear to chase down. Hard to believe there's not a tech in ABQ. Even if you have to drive a distance.
 
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