Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Pick-n-Strum on June 15, 2021, 08:00:47 pm

Title: Very Loud "Singing" PT
Post by: Pick-n-Strum on June 15, 2021, 08:00:47 pm: So I just picked up a Peavey Prowler for dirt cheap. It works fantastic other than an incredibly loud singing power transformer. This is a mechanical sound inside the chassis and I am certain it's the PT. When the chassis upside down, I can get the sound to go away almost completely by wedging in a shim between the chassis and laminations. Wondering what my options are for quieting this down...

I've read a little bit on wax potting but have no experience with it. Is it possible to do this just to quiet down the laminations? I'd preferably like to leave the PT in the chassis but I can remove it if necessary. Any other suggestions or tips on fixing this / wax potting? I know I mentioned a shim above but I'd prefer to do something a little more permanent - I feel like a shim will just vibrate right out...
Title: Re: Very Loud "Singing" PT
Post by: sluckey on June 15, 2021, 08:32:32 pm: Have you tightened the mounting bolts?
Title: Re: Very Loud "Singing" PT
Post by: PRR on June 15, 2021, 09:43:31 pm: Many amps sing on the test bench with dummy-load. Is this one really so loud you hear it above a speaker?

> I feel like a shim will just vibrate right out...

Not if you glop it in ShoeGoo or similar stick-um.

Also loosen bolts, shim, then tighten.
Title: Re: Very Loud "Singing" PT
Post by: mresistor on June 16, 2021, 08:13:35 am: Quote from: PRR on June 15, 2021, 09:43:31 pm
Not if you glop it in ShoeGoo or similar stick-um.

I can attest that ShoeGoo is some pretty awesome stuff! Also Toyota FiPG is pretty good for making gaskets.
Title: Re: Very Loud "Singing" PT
Post by: Pick-n-Strum on June 16, 2021, 09:01:18 am: Quote from: sluckey on June 15, 2021, 08:32:32 pm
Have you tightened the mounting bolts?

Meant to say in my OP that I did tighten the mounting bolts and it didn't help.

Quote from: PRR on June 15, 2021, 09:43:31 pm
Many amps sing on the test bench with dummy-load. Is this one really so loud you hear it above a speaker?

> I feel like a shim will just vibrate right out...

Not if you glop it in ShoeGoo or similar stick-um.

Also loosen bolts, shim, then tighten.

Ahh - makes sense! Any preferred material for the shim itself? I assume wood is a no go since the PT can get pretty hot...What do you guys recommend?

Quote from: mresistor on June 16, 2021, 08:13:35 am
Quote from: PRR on June 15, 2021, 09:43:31 pm
Not if you glop it in ShoeGoo or similar stick-um.

I can attest that ShoeGoo is some pretty awesome stuff! Also Toyota FiPG is pretty good for making gaskets.

I've used gasket maker on speaker cones and an ATV - it does work wonders!

EDIT: I was looking for some materials I could use that would be safe. I've got some G10 board rated for 265 degrees. Mercury Magnetics put out an article indicating that the safe limit for PTs are 200 degrees. Assuming my PT falls in that safe limit, I should be good to go using the G10 as shims. Bonus, I had some hi-temp gasket maker as well!

Thanks for the help!
Title: Re: Very Loud "Singing" PT
Post by: PRR on June 16, 2021, 11:58:58 am: If a transformer sets wood on fire, it is already toast.

gee. I use sticks to rattle-shim my exhaust manifold. My mechanic may not like it, but they come out hardly scorched.
Title: Re: Very Loud "Singing" PT
Post by: mresistor on June 16, 2021, 12:20:32 pm: You could use extra nuts and washers to get it tight and it might be a plus to have a gap where it mounts to allow for airflow.