Combo Amp Tube Rattle

[river rat]

I have an Epi Valve Jr. Recently, I have been noticing a serious "tinny rattle " after the amp has warmed up. At first I thought it might be my new Weber Blue Pup , but I put the original speaker back in and the rattle was still there. This amp has 1-12ax7 and 1- EL84. I have read that EL84's are notorious "rattlers" in combo amps. BTW,I swapped out the EL84 and the rattle is still there to a somewhat lesser extent. Does anyone have any advice / solutions. Thanks...

[The Kirbster]

I have seen some tube dampers (don't recall exactly what they called them). Basically they were hi-temp silicone O-Rings that were installed around each tube to cut down on microphonics. Sounded like a neat but kinda expensive solution, so I bought a tube of hi-temp silicone & "squirted" my own dampers around the middle of each tube. Now, this was intended to calm down MICROPHONICS, so I don't know if it'd be enough to fix an out & out RATTLE. If you already have some silicone around the house, it might be worth a try. I have also put pieces of fiberglass insulation inside the metal covers for my pre-amp tubes in an old Super Twin that was notorious for microphonic tubes, and it helped too. If something is loose enough inside one of your tubes that it rattles, I'd consider replacing it anyway. I've got a pair of Epi Junior heads-neat lil' amps to play with!

[Steve Conner]

Try tapping the tubes while it's on. If one of them is microphonic you'll hear a ping/rattle through the speaker.

EL84s are famous for this, I have an EL84 amp that does it too. But any tube can go microphonic in a combo amp.

[Gtr_tech]

Yep.....EL84s in combos don't tend to last too long. They're just not a mechanically robust tube and the internals tend to get rattled loose in short order. I tell my customers with 84 combo amps to treat the output tubes like strings......change them out when things start sounding bad. Damping the glass envelope does nothing to keep the internal structure from rattling once it starts happening.....

[river rat]

O.K. ,so once it starts there's little that can be done. Is there anything I can do to help prevent it happening to a replacement tube?
Will tube dampeners help in that regard? This amp doesn't have a proper tube shield for the "EL", just a somewhat flimsey retainer. Any ideas?
Thanks...

[Chuck H]

It would seem like a strictly mechanical issue but I have noticed that el84 amps that push the tubes hard seem to go rattley sooner. My personal amp uses a pair of el84's at 355Vp biased about 90% and the tubes last a good five or six months. A little Mesa combo I modded has 400Vp with the tubes very near 100% and just ruins them in about three months. Same tubes too, experiment repeated add nausium.

IMHE el84's when pushed even a little start to lose their rich 'n' tasty goodness after about 150 hours. So if they don't go rattley before that your amp isn't over abusing them prior to needing replacement anyway.

If you do feel the tube is rattling prematurely something that has worked for me is a pad under the tube. I've used cork, rubber gasket material and a blob of silicone all with equal results. Just place a thin pad between your tube and the socket and snap on the retainer. It must be thin enough to allow the tube pins to contact. This will extend tube life better than the slip on dampers, I promise.

Don't use any black rubber. Black rubber is made black by the addition of carbon. With the highish voltage on power tubes it can actually become a conductive material. There's a story about why I know that BTW

[olddawg]

Not to highjack this thread, but I have an 18 watt EL84 amp with the tubes mounted horizontally. The EL84s seem to go rattlely much sooner. I've seen HiFi amps with EL84s mounted at a 45 degree angle or horizontally. I guess if you drive them hard and they are not straight up you get more problems. I have a VJ head also. Best bang for the buck out there. Put some NOS tubes in it.

[Gtr_tech]

I believe that is due to filament sag.....

[Chuck H]

I do know that as "I" get older (and things start to sag) things do rattle more. And the harder I push myself the more I rattle.

The Russian 6p14pe tube is supposed to be more durable also and less prone to this.

[Gibsonman63]

Here are some reasonably priced dampners from the AmpGarage site. This is from the Express BOM:

Magnan Audio Cables Web Site - Tweaks: Tube dampers

FEP Teflon coated silicone o-rings, size 116, fits miniature (12AX7-size) tubes, silicone o-rings, size 133, fits 2A3 an 300B types: McMaster-Carr (562) 692-5911, catalog numbers 9319K26 (#116), 9396K154

This is for 12AX7 and EL34 size tubes. I would assume you could find one that will fit an EL84

[olddawg]

Here are some reasonably priced dampners from the AmpGarage site. This is from the Express BOM:

Magnan Audio Cables Web Site - Tweaks: Tube dampers

FEP Teflon coated silicone o-rings, size 116, fits miniature (12AX7-size) tubes, silicone o-rings, size 133, fits 2A3 an 300B types: McMaster-Carr (562) 692-5911, catalog numbers 9319K26 (#116), 9396K154

This is for 12AX7 and EL34 size tubes. I would assume you could find one that will fit an EL84

I have never tried it, but I have been told that you can just go to the hardware store and buy a couple of red rubber "O" rings of the appropriate size and thinkness. The red are supposed to not melt like the black ones. I have also been told that is all the people on eBay are doing except putting them in a fancy bag and charging 1000 times what they paid for them.

[Gibsonman63]

One of the places I occasionally buy tubes from was selling them for about $25 a pair. Good margain if you can get it.