Tube Question

[treyhaislip]

Apologies in advance for my ignorance here.

Quick background, recently got my Fender Blues Deluxe back from a local shop (Acorn Amps) and they recommended I get tube dampers to help with some of the rattle noise (wasn't a big deal but was enough to be noticeable.)

So I buy several and put them on all of the tubes (6L6s and 12Ax7s...different sized dampers for the different sized tubes.) Great, no more tube rattle. Sounds just as good as before–

But...now every "G note" (standard 440 tuning) makes a rattle/squeal. I checked to make sure the tubes were plugged in correctly and feels like there are good to go. Isolated it to specifically G notes anywhere on the neck...only does it on a G...

Is that a bad tube? Is there a remedy for this or just time to get new tubes? (which the tubes were replaced in early May.)

Thanks for the help!

 

[LLL]

Re: Tube Question

Could just be a microphonic tube... it still works, but squeals with unwanted feedback.

I have a NOS Mullard CV4004 that does that.

You see, it all has to do with earth vibrations and such. You must attune yourself and all your gear (tubes/valves too) to the Golden Frequency of 432Hz... before the ice caps melt away...

 

[Darg1911]

Re: Tube Question

It's probably one tube (hopefully). Isolate it by removing the dampers, one by one. I'd start with one of the 6L6's. They were probably the source of the rattle rather than the 12AX7's (assuming it was a physical rattle of the internal tube structures). Sounds like you traded rattle for microphonics.

 

[treyhaislip]

Re: Tube Question

Just heard back from Acorn Amps, they said to re-position the dampers and add another one to see if it helps and if it doesn't to just bring the amp back in.

Does sound like I traded rattles for microphonics. lol And it is definitely with the 6L6s, I got the 12Ax7 dampers in several days before the 6L6s (no microphonics until the 6L6s.)

The microphonics are worst than the rattle, but worst case scenario I just get a new tube(s). Thanks!

 

[IM4Tone]

Re: Tube Question

I was going to suggest repositioning the dampeners. Also, I've used two dampeners per tube.
I'd be surprised if applying dampeners caused microphonics. Assuming the 6L6's are a matched pair, swap their locations....simple enough to try.

 

[treyhaislip]

Re: Tube Question

I was going to suggest repositioning the dampeners. Also, I've used two dampeners per tube.
I'd be surprised if applying dampeners caused microphonics. Assuming the 6L6's are a matched pair, swap their locations....simple enough to try.

Well, they currently have 2 on them–will try to reposition the dampers as well as swap the locations.

The dampers definitely cut out the tube rattling–so I'd prefer to keep them on...but the tube rattle wasn't that bad if they need to come off.

Thanks for the input!

 

[Darg1911]

Re: Tube Question

To be clear, I agree with IM4. I believe that the tube was already microphonic. I'm thinking that it's not the damper causing the microphonics but shifting the frequency at which the tube is "excited" ... if that makes any sense. If removing the dampers returns the rattle but eliminates the G note issues, then that should confirm it. I don't understand the physics, obviously, but I've had similiar happen before where tube damper fixed one issue only to expose another that was more annoying than the original.

 

[treyhaislip]

Re: Tube Question

To be clear, I agree with IM4. I believe that the tube was already microphonic. I'm thinking that it's not the damper causing the microphonics but shifting the frequency at which the tube is "excited" ... if that makes any sense. If removing the dampers returns the rattle but eliminates the G note issues, then that should confirm it. I don't understand the physics, obviously, but I've had similiar happen before where tube damper fixed one issue only to expose another that was more annoying than the original.

I'm no expert at all on tubes...not an expert at anything for that matter. lol

Since it wasn't "acting" microphonic before the dampers I'm hoping with some adjustment I can get it back to what it was before...might not but at least others have had the same thing. Really appreciate the input!

 

[Jacew]

Re: Tube Question

I'm no expert at all on tubes...not an expert at anything for that matter. lol

Since it wasn't "acting" microphonic before the dampers I'm hoping with some adjustment I can get it back to what it was before...might not but at least others have had the same thing. Really appreciate the input!

If I understood right, the problem seems to be the microphonic tube, that you only noticed after installing the dampers. So if you get where it was before, you'll be really just masking the problem, not fixing it...

Unless they're some NOS, or other expensive set of tubes, I would just locate and replace that particular tube.

 

[Chickenwings]

Re: Tube Question

IN my experience, tube dampers are snake oil. They dont hurt, but they really cant help a microphonic tube.
I would be eliminating the possibilities of internal tube failure first, but then also be looking at the tube seats, and a real big one on all the hotrot series amps is rattles from the cabinet itself.

 

[treyhaislip]

Re: Tube Question

Update: Swapped the two 6L6s around and widened the distance between the dampeners, no more noise.

So that fixed (or resolved/masked) the problem I was having. Thanks for all of the input and advice!

 

[LLL]

Re: Tube Question

IN my experience, tube dampers are snake oil.

Bingo.

 

[treyhaislip]

Re: Tube Question

Bingo.

They reduced the tube rattle on this amp...

 

[Little Pigbacon]

Re: Tube Question

They give people like me something to do.

 

[Little Pigbacon]

Re: Tube Question

IN my experience, tube dampers are snake oil. They dont hurt, but they really cant help a microphonic tube.
I would be eliminating the possibilities of internal tube failure first, but then also be looking at the tube seats, and a real big one on all the hotrot series amps is rattles from the cabinet itself.

Hotrot. I'll have to remember that one.

 

[Chickenwings]

Re: Tube Question

derp

 

[Darg1911]

Re: Tube Question

They reduced the tube rattle on this amp...

They should be good for something like that. I have a slightly microphonic tube in a phono stage that I built. You are supposed to use low noise tubes for phono stages for obvious reasons. But this long plate RCA sounds excellent so I made a tube damper out of a spring type wire and silicone rubber. I filled a paper straw with silicone rubber, let it cure for a few days and then ripped the straw open to get the silicone tube. Cut the silicone rubber into small sections. Formed the wire around a piece of tubing quite a bit smaller than the tube so when it sprung back it would still be a tight fit around the tube. Poked holes in the silicone pieces and placed several on the wire that I formed into a spiral. No way would that tube work out in a combo amp or any loud application but that damper quieted the ringing down enough that it's quiet in the relatively low powered home audio system. That was years ago and it still works to this day. I know I'm a bit off topic, but the point is that I would disagree that tube dampers are "snake oil". They aren't going to make a microphonic tube non-microphonic but they definitely can mask the issue in SOME situations. It's a bandaid that works, sometimes.

 

[treyhaislip]

Re: Tube Question

I agree, this is not the first tube amp I've had them on, they've always reduced the tube rattle noise. This is just the first time that putting them on caused the microphonics.

 

[IM4Tone]

Re: Tube Question

........................the point is that I would disagree that tube dampers are "snake oil". They aren't going to make a microphonic tube non-microphonic but they definitely can mask the issue in SOME situations. It's a bandaid that works, sometimes.

My experience as well.