Wild Bill and other amp gurus

[dr_iggi]

Hello there! This is a question for Wild Bill and other amp gurus.

I have this nice clone of a vintage AC15 1x12 combo: EF86 preamp, 12AX7 phase inverter, 2xEL84s in push-pull configuration and a 5AR4 rectifier.

There is a fair amount of metallic/glassy rattle at med-high volumes. I am almost positive that the offending tube is the EF86. I have tried 3 different JJ tubes, but they all rattle within a short time and with med-high volumes.

I have read that the current production EF86s are average at best. I love the tone, but hate the rattle... how can I fix this problem without trying dozens of current production EF86s or buying NOS tubes, which might be an expensive lottery anyways?

I would love to keep the combo format (rather than a head). Can this be solved by heavily dampening the chassis, the tube shield, and the plastic light cover nearby the EF86?

Is this M3-1 EF86/6267 adaptor a possible solution http://www.guitaramplifierblueprinting.com/mitch.html ? Any ideas how any of these tubes (6AU6, 6BA6, 6AK5) will affect the tone?

Or should I simply give up on this amp??? :-(

[Geek]

Hi,

Is the tube the offending problem? Does it "ping" when you tap it to the level of the glassy rattle you speak of?

If so, before spending tonnes on money on other solutions, try getting some silicone O-ring seals from an auto parts place and place two around the EF86. Could cure your problem for a dollar.

The closest in performance to an EF86 is a 6EJ7. But EF86 is the *least* microphonic of everything listed and I've tried. Some brands for the others (like 6AU6) are definately better than others. NOS/used Rogers (Canada) and Philips are some of the best.

Cheers!

[Wild Bill]

This is a common problem, with no easy solution I'm afraid. Th O-ring is a good suggestion but it's a crap shoot as to whether or not it will work well enough for you. You might get lucky and it's cheap to try.

New production EF86's do tend to rattle. Old German tube radios are often a great source of original EF86's. Watch the yard sales and flea markets. I wouldn't destroy a restorable radio but there's still a surprising amount of bashed up junk out there.

It's a bit of work but an old hifi trick for microphonics in tubes is to mount the tube socket on longer screws with small rubber grommets. Rubber ones are usually pale white or tan in colour and seem to be hard to find these days. Neoprene are common but being stiffer may not work as well to damp out vibration transfer.

You could also copy a trick used with a lot of old reverb spring tanks. Using small washers, long small screws and springs stolen from cheap pens (you might have to cut them shorter) you can "float" the socket.

Original EF-86's are like gold!

:food-smiley-004:

[nonreverb]

Hello there! This is a question for Wild Bill and other amp gurus.

I have this nice clone of a vintage AC15 1x12 combo: EF86 preamp, 12AX7 phase inverter, 2xEL84s in push-pull configuration and a 5AR4 rectifier.

There is a fair amount of metallic/glassy rattle at med-high volumes. I am almost positive that the offending tube is the EF86. I have tried 3 different JJ tubes, but they all rattle within a short time and with med-high volumes.

I have read that the current production EF86s are average at best. I love the tone, but hate the rattle... how can I fix this problem without trying dozens of current production EF86s or buying NOS tubes, which might be an expensive lottery anyways?

I would love to keep the combo format (rather than a head). Can this be solved by heavily dampening the chassis, the tube shield, and the plastic light cover nearby the EF86?

Is this M3-1 EF86/6267 adaptor a possible solution http://www.guitaramplifierblueprinting.com/mitch.html ? Any ideas how any of these tubes (6AU6, 6BA6, 6AK5) will affect the tone?

Or should I simply give up on this amp??? :-(

Funny you should mention this...I recently had one of the new point to point Vox AC 30's in the shop. When I got it apart, I found the EF86 sealed in what could only be described as a cushioned blanket surrounding the tube from top to bottom. So it appears that Vox is well aware of the problem with "new" EF86's too.

[Geek]

Hi,

You could also copy a trick used with a lot of old reverb spring tanks. Using small washers, long small screws and springs stolen from cheap pens (you might have to cut them shorter) you can "float" the socket.

That's a great suggestion and was going to be my second if the O-rings failed, but the ones from AES. Bill's DIY solution sounds far more efficient :food-smiley-004:


Original EF-86's are like gold!

For sure. There's a reason those Telefunken's go for $100+ and Siemens right behind them :wink:

Cheers!

[dr_iggi]

Thanks for all the replies. I will go with rubber grommets first in an attempt to isolate the socket from vibration. It certainly seems like a more sensible solution than dropping $100 of NOS tubes, which will get even more expensive.

[dr_iggi]

Original EF-86's are like gold!

FWIW, here is a dude selling NOS Telefunken EF86s for $70 (maybe a bit more shipping to Canada) http://www.thegearpage.net/board/showthread.php?t=398906