Fixing a rattling tube

Trem2 · Post by **Trem2** » Fri Mar 24, 2006 9:28 am

Anyone know of a way to remedy this problem ?
When I play certain notes on my electric it rattles the tubes and I get that glassy rattling sound coming out of the amp. Really annoying when trying to record.
Seems like its a common thing cause most of my old tube amps have this problem. There must be a fix.

A-Barr · Post by **A-Barr** » Fri Mar 24, 2006 9:32 am

They have become microphonic. There are 2 solutions: 1) Isolate the amp from the speakers - not really possible in combo amps - or 2) Replace the tube.

RodC · Post by **RodC** » Fri Mar 24, 2006 9:55 am

Yep, chances are if they are microphonic they are going to sound better when you replace them as well. Your amp will probably be quieter also, A lot of Microphonic tubes will start to resonate with all the 60Hz in the amp and can cause hum.

Trem2 · Post by **Trem2** » Fri Mar 24, 2006 12:27 pm

Wow- Interesting. Is this just something that happens with old tubes then ?
This amp is from the 60's and still has the original tubes in it so, probably would help it out to replace the tubes.

Thanks for the replies.

RodC · Post by **RodC** » Fri Mar 24, 2006 12:32 pm

Yep it will happen to new ones as well. I got a bad lot of EH 12ax7s one time, 4 out of 6 went microphonic within about 4 hours of play time. I bet it was bad welds from the factory. Of course it will happen faster in tube amps that are carried around a lot, vibrations, especialy when hot, are bad news for tubes.

I belive it is mostly caused by parts of the tube coming apart inside and when you vibrate them they act just like a signal/microphone.

Brian Brock · Post by **Brian Brock** » Fri Mar 24, 2006 12:53 pm

Hmmm... There's also a well-known problem of certain Peavey amps, like the Delta Blues, which have poorly mounted tubes which will rattle when new. You can make/buy a thing to hold them tighter.

b

Milkmansound · Post by **Milkmansound** » Sat Mar 25, 2006 7:17 am

a corroded socket can also cause this problem - but its probably just the tube being microphonic - spend the $6 and replace it

Marik · Post by **Marik** » Sat Mar 25, 2006 4:00 pm

Before you discard the tube I'd try to use a tube dumper, or electrostatic shield with a spring. Both can greatly reduce the tube ringing effect.

Trem2 · Post by **Trem2** » Sat Mar 25, 2006 4:39 pm

Never really heard of a tube dumper or an electrostatic shield. Guess its time to do some googlin.

brianroth · Post by **brianroth** » Sat Mar 25, 2006 11:00 pm

I believe Marik meant to say a tube DAMPER (dumper is where I do a lot of my reading...heheheh).

The tube shield is commonly used in Fender amps and such, and looks like this:

http://www.aydn.com/product_info.php?products_id=62

There is an internal spring at the top of the shield (barely visible in the pic) that helps hold the tube and shield in place.

However, those shields require a tube socket with the proper design to hold the shield in place. Typically, the socket and shield are sold as a set.

Bri

crow · Post by **crow** » Tue Mar 28, 2006 10:10 pm

Hmmm... There's also a well-known problem of certain Peavey amps, like the Delta Blues, which have poorly mounted tubes which will rattle when new. You can make/buy a thing to hold them tighter.

that's definitely a loose tube socket rather than the tube itself. an important distinction to make is whether the rattle is being amplified (i.e. audible in the speaker) or just plain ol' rattling. if you're certain that you're hearing it from the speaker, then it's definitely a bad tube. to figure out which bad tube, gently tap each one with the eraser end of a pencil or some such item (with the amp on and set up as though you are playing through it). if you hear ringing or rattling come out of the speaker when you do that, you've found your microphonic tube. go ahead and replace it.

on the other hand, it could be just a loose part of the amp that vibrates when the amp is too loud. often, it's a loose tube socket, which can be replaced or tightened (be EXTREMELY careful if you try to mess with this yourself! I once absentmindedly touched the wrong pin of a socket (knowing better) and was caused to scream a cuss word in a hyena-type voice. it could also be any loose part of the amp(springs, screws etc.), which sometimes leads to a maddening goose-chase. A Vox AC30 recently gave me all kinds of hell in this department.

1) Isolate the amp from the speakers - not really possible in combo amps

actually, in an emergency, you can often remove the "head" part of a combo and treat the amp as a "head-and-cabinet" setup if you have the right cables to do the trick. this saved my ass a few times.

sorry to be so long-winded, but i guess i spend a lot of time trying to get fucked-up amps to give us one more song. right now!

[/quote]

mingus2112 · Post by **mingus2112** » Wed Mar 29, 2006 6:40 am

Trem2 wrote:Wow- Interesting. Is this just something that happens with old tubes then ?
This amp is from the 60's and still has the original tubes in it so, probably would help it out to replace the tubes.

Thanks for the replies.

I wouldn't go jumping to replacing all of the tubes just yet. Certainly buy a new preamp tube to replace the rattling one for now. Either gig with a full extra set of tubes (power tubes) or with a solid state backup amp until the power tubes that are in there now go! The amp might sound MEGA different if you go replacing all of the old tubes with new ones! You'll also need to rebias the amp with the new tubes (although i've gone without it if i'm using tubes that are tested the same).

What kind of amp is it?

-James

Trem2 · Post by **Trem2** » Wed Mar 29, 2006 7:23 am

Its an Ampeg Gemini 1 from the 60's. And I found the offending tube and tapped it a bit. Got that glassy ping coming out of the speaker. Definitely a microphonic tube.
I think I might try one of those tube damper thingys to start off with since they are pretty cheap. I like the sound of this amp with the old tubes in it. I also have a Gemini 2 that I replaced all the tubes in and it definitely sounds different now.

nclayton · Post by **nclayton** » Wed Mar 29, 2006 10:37 am

Trem2 wrote:Its an Ampeg Gemini 1 from the 60's. And I found the offending tube and tapped it a bit. Got that glassy ping coming out of the speaker. Definitely a microphonic tube.
I think I might try one of those tube damper thingys to start off with since they are pretty cheap. I like the sound of this amp with the old tubes in it. I also have a Gemini 2 that I replaced all the tubes in and it definitely sounds different now.

Sorry to only add more confusion to the subject, but was the tube you got to ring a 12ax7 far away from the power tubes? It's pretty much impossible to put a tube in the first gain stage of an amp and have it not ring a little bit when you tap it. If it was a 12ax7 early in the circuit, you could go ahead and replace it and see if it helps, but it may and may not.

I find that rattling as opposed to ringing type microphonics TEND to be power tubes more often than preamp tubes, but with a Gemini you probably have 7591 power tubes in there (?). If you can avoid replacing those you should since the new ones don't sound the same, and the old ones sound fantastic. Hopefully replacing that preamp tube will do the trick.

Ned

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Fixing a rattling tube

Fixing a rattling tube

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