Amp screech...little help?

[krankguitarist]

This time its my KRANK.

I'm assuming I got a bad set of tubes...as this didn't happen before today, and I just replaced and biased the tubes today.

Anywho...here's the deal:

I plug in, I turn on, and there seems to be a whole lot more noise than there should be. Wait a few seconds, and the amp goes "SCREEACHHHHHH". Doesn't last longer than a second...and it doesn't repeat. At least, that I know of. I've been turning it off right afterwards :eek13: .

Happens with or without a guitar plugged in...distortion and clean channels.

As of right now...I'd put in the old set of tubes again, but its late and my 'rents have already yelled at me once cause of it. So that'll have to wait till morning.

This sorta thing ever happen with any of ya'll?

 

[rog951]

Re: Amp screech...little help?

Hmmm. I've never heard a screeching sound come out of my amp, at least not by accident! I guess it stands to reason that it's something with your power tubes since that's what just changed. If it turns out a tube is bad, I hope you bought from someplace with a good return policy! Good luck!

 

[krankguitarist]

Re: Amp screech...little help?

t'was both the power tubes and the preamp tubes that I replaced. Got my stuff from eurotubes...AFAIK, they have a good reputation...I'm sure if its the tubes at fault I'll be able to work something out with them.

 

[krankguitarist]

Re: Amp screech...little help?

Hmmm...well, I decided the suspense was too much, so I lugged the thing to the other side of the house...where my 'rents cant hear it...and tested it out again. Changing out the preamp tubes didn't seem to do much. Swappin the power tubes did though. Seems to have solved the problem. Still gonna keep an eye on it, test it out a bit more. If it is the power tubes though...well...I guess I'll just have to contact Bob down at eurotubes and see if I can't get a replacement.

 

[Mephis]

Re: Amp screech...little help?

Yea rarely do preamp tubes cause issues in my experences.

It's almost always going to be the most expensive thing that takes a dive. In this case, powetubes.

 

[krankguitarist]

Re: Amp screech...little help?

I'm gonna test those tubes in my KRANK and showman tomorrow...see if I get the same result. Good thing about having two amps that use 6l6's.

Though...to be honest the most expensive thing in there would probably be the mercury magnetics transformers. If one of those was to take a dive I'd be bawling like a baby. Not really. But seriously. I would.

 

[Mephis]

Re: Amp screech...little help?

I'm gonna test those tubes in my KRANK and showman tomorrow...see if I get the same result. Good thing about having two amps that use 6l6's.

Though...to be honest the most expensive thing in there would probably be the mercury magnetics transformers. If one of those was to take a dive I'd be bawling like a baby. Not really. But seriously. I would.

I meant the most expensive of the 2.

Being preamp or poweramp.

 

[WhoFan]

Re: Amp screech...little help?

Yea rarely do preamp tubes cause issues in my experences.

It's almost always going to be the most expensive thing that takes a dive. In this case, powetubes.

Pretubes have cause feedback like noises in my C50 head.... tapped on the tube and it was really ALIVE... microphonic...

 

[krankguitarist]

Re: Amp screech...little help?

Yup...its definitely those 6l6GC's. Just tested it out in my showman and my KRANK again today...does the same thing in both amps. Kinda like a mix between nails on a chalkboard and a very loud zipper. Either way, I gotta call up the guys at eurotubes and try to see if I can't get a replacement.

 

[krankguitarist]

Re: Amp screech...little help?

Well, little update here...I narrowed it down to the offending tube, and now I'm getting a replacement sent to me from eurotubes w/o having to send the bad tube back. Now that's customer service :headbang: .

 

[aleclee]

Re: Amp screech...little help?

I plug in, I turn on, and there seems to be a whole lot more noise than there should be. Wait a few seconds, and the amp goes "SCREEACHHHHHH". Doesn't last longer than a second...and it doesn't repeat. At least, that I know of. I've been turning it off right afterwards :eek13:

Gawdawful noise from a Krank? Isn't that their signature tone? Seriously, glad to know that it was just a bum power tube and that nothing else was amiss in your amp.

Yea rarely do preamp tubes cause issues in my experences.

As far as weird tones coming from an amp, my experience has been the opposite, especially in higher-gain amps. Like WhoFan pointed out, a microphonic preamp tube can create quite the sonic maelstrom.

 

[Scott_F]

Re: Amp screech...little help?

I had that type noise one time when I had the primary taps on an Output transformer wired backwards. annoying sound, especially to parents that are trying to sleep!!! And, yes, Bob at Eurotubes is a good guy.

 

[doveman]

Re: Amp screech...little help?

What about filter caps? I've been researching replacing my 30 year old filter caps ... those big electrolytic high voltage capacitors near the transformers. My amp is losing volume occasionally ... thats my symptom.

But it seems like I remember something about screeching when they are failing. I'm not a tech ... going from memory ... I could be wrong.

 

[Scott_F]

Re: Amp screech...little help?

filter caps are only supposed to be good for 10 years or so.

 

[doveman]

Re: Amp screech...little help?

i know ... mine are original and beginning to give me trouble. My tubes lasted 27 years ... they are not supposed to do that either. Just lucky I guess. I play it just about every day too.

Edit: Now that I think about it ... when I retubed the amp ... 2 of the 3 pre-amp tubes V2 and V3 went back in the amp. So only V1 and the 6L6s have been changed. Ordering the filter caps this week though.

 

[Scott_F]

Re: Amp screech...little help?

Preamp tubes can last a very long time. Rectifiers as well.

 

[doveman]

Re: Amp screech...little help?

My son and I changed tubes in his amp this weekend. When he turned it on it would feedback for a second and then stop. I thought of this thread. Turned out that the only fix was when we changed the 1st 12ax7 out ... it stopped. It wasn't really microphonic ... it only did it once each time you turned the amp on. Never seen that before.