Amp/tube Rattle?

buzzp

Member
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6,913
So my old ampeg doesn't like it when I get too loud, you can hear the rattle a bit "behind the note" if that makes sense. I inspected a bit this morning, and I think I've narrowed down one of the power tubes, or the tube sockets. When I knock on the chassis, the rattling noise gets reproduced, but the volume level of that rattle drops when I remove the power tubes.

Any suggestions? Any more info that would help? I would like to save a trip to the amp tech if possible.
 

Blue Strat

Member
Messages
30,183
So the rattling isn't amplified, only heard acoustically?

If there are tube retainers on the power tubes remove them temporarily as a test. They'll often rattle.

If you have spare power tubes try them to be sure that they don't rattle. If not, try each of the suspect tubes, one at a time, with a good tube to see if you can narrow it down to one tube or the other.

Some will say to shake the tubes in your hand and listen for rattles. This probably won't help because lots of power tubes will produce some noise when doing this but act perfectly in an amp.

Many times the rattling that people hear is not the tube or sockets, but the tube bases rattling against the face of the sockets. Installing some heat resistant gasket material, with holes punched for the tube pins, between the tube socket and tube base will cure this.

Before spending money and time taking it to a tech it would make more sense to try a new pair of power tubes. You're going to need them sooner or later anyway.
 

NoBrakes

Member
Messages
2,744
probably just old worn tubes. el-84s are notorious for doing that when they get old. I've seen it in other types too.
 

buzzp

Member
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6,913
Fwiw these seem to be original 7591 power tubes (ampeg labeled). I'm going to try the tube retainer and heat gasket trick though.

The rattle does come through when amplified, if it didn't I wouldn't care as much.
 
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Blue Strat

Member
Messages
30,183
Fwiw these seem to be original 7591 power tubes (ampeg labeled). I'm going to try the tube retainer and heat gasket trick though.

The rattle does come through when amplified, if it didn't I wouldn't care as much.
If it's amplified try tapping on each power tube with the amp on. If either produces noticeable rattle when you do this you'll know what the problem is.

Original 1960's power tubes? ;)
 
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buzzp

Member
Messages
6,913
If it's amplifiedtry tapping on each power tube with the amp on. If either produces noticeable rattle when you do this you'll know what the problem is.

Original 1960's power tubes? ;)
Ha, yeah, I know... do you like the JJ repros of the 7591? I know the NOS ones are supposed to be vastly superior, but it's quite the cost difference.
 

Blue Strat

Member
Messages
30,183
Ha, yeah, I know... do you like the JJ repros of the 7591? I know the NOS ones are supposed to be vastly superior, but it's quite the cost difference.
Haven't tried them. 7591s are a low priority due to very low demand. I'd bet $5 that the JJ's won't last as long as your "NOS" tubes did. ;)
 

thekaiser

Gold Supporting Member
Messages
465
I don't think it's a preamp tube. But I'll try that
Maybe this goes without saying, but don't just grab a tube while the amp is on. Dampen it with the like of an eraser of something but do not make contact with your hand.
 

vicdeluca71

Member
Messages
1,502
With the heat of of tubes and the voltage running through both them and other components is the amp, it could go real wrong, real quick.
You serious? Crossing the street can go "real wrong, real quick" . Next time you have a microphonic tube go behind your amp and pinch each tube til you find the culprit. Quickest and easiest way, you'll be alright.

Op, I've owned plenty of el84 combos and some were impossible to tame the microphonics due to cab design. I did my research years ago which lead me to the Russian 6p14p-k (el84) and this solved that problem. On the bay there are a ton of these NOS. They are cheap and sound awesome. Make sure you get the k designation they are vibration resistant ones
 

Guinness Lad

Member
Messages
15,862
Buy a packet of O-Rings like I said before. It will cost you $20 maybe for everything you need, probably less. 12ax7 and el84 tubes can use the same ring, so buy rings for 12ax7 tubes.

Put them on one tube at a time, or all of them. Not even sure why this is being argued, the solution is obvious. If the tube is going to fail anyway or the damage is more serious than what a O-Ring can squelch, then you will need to replace it anyway.
 




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