Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on June 13, 2010, 02:57:07 pm

Title: Power tubes rattle in the combo
Post by: Leevi on June 13, 2010, 02:57:07 pm

I have noticed a relative high frequency mechanical rattle coming probably from a pair of EL84.
That happens only with a specific note (=B). Is that typical for JJ's EL84?
/Leevi

Title: Re: Power tubes rattle in the combo
Post by: phsyconoodler on June 14, 2010, 01:22:11 pm

It can happen with EL84's of all types.
 A better tube retainer system can help.

Title: Re: Power tubes rattle in the combo
Post by: simonallaway on June 14, 2010, 01:56:44 pm

Surely this is a problem for all tubes in a combo? or does it depend on the cab design, size of tube. I am wondering if the resonant frequency of any given tube is predictable.

Title: Re: Power tubes rattle in the combo
Post by: Searing on June 14, 2010, 02:03:13 pm

I had the same problem with my Twin loaded with Phillips 7581A's.  Couldn't really hear it at gigs or practice though, but it did drive me nuts for a bit.  Switched recently to JJ 6L6's and it was gone.  The 7581's were great just rattley and or microphonic.  So it does occur with other tube makes.

Chris

Title: Re: Power tubes rattle in the combo
Post by: phsyconoodler on June 14, 2010, 02:20:25 pm

Or a vibration shield between the speaker and the tubes.Something that doesn't vibrate itself.I would use something like what a guy on e-Bay used to sell for Peavey Classic 30 amps.It's a tube retainer that clamps the tubes.
  Or you could use individual tube clamps with heat-proof linings like Tone-King amps and Badcat amps use.It makes it a pain to change tubes but ensures that they don't rattle at all.