Problem with tube amp

Martin Abend · From: Berlin, Germany

Hi,

I bought a very nice little tube amp recently. The design is almost similar to a Fender Pro Junior, but it's hand wired and sounds just great.

About to weeks ago that buzzing sound started. It's not there when I turn the amp on, but the warmer it gets the more it buzzes. After, like, 10 Minutes it's really loud and annoying, as if there's a little electric razor in the back. The buzzing does not come the the speaker, it's only coming from the back.

I talked to someone from the store and they said that one of the power amp tubes is blown, but I'm doubing it...

Here's a recording of it:
http://www.ipernity.com/doc/catandriver/546748

What do you think?

Thanks for your help!

MArtin

Mike Wheeler · From: Delaware, Ohio, USA

Martin, from your description, it would suspect something related to the power transformer. It could be the result of loose mounting hardware, or even from the transformer itself. The sound increasing as the amp warms up points in that direction also.

It might be best to return it for a replacement, or if the seller had a tech shop, they could fix it for you. I also don't believe the "blown tube" explanation...you would here that thru the speaker.
_________________
Best regards,
Mike

Ken Fox · From: Nashville GA USA

Sounds like loose laminations in the power transformer.

You can usually feel the transformer and tell if it is vibrating.

Clyde Mattocks · From: Kinston, North Carolina, USA

Ken's suggestion of vibrating laminations in the transformer is very plausible. I don't want to get too technical here, but you might try a C clamp on the transformer. All kidding aside, sometimes jackleg techniques actually work. I had a Princeton
with the components mounted on those "tar paper" strips that buzzed. I noticed that if I pulled up on the mounting boards, it would stop. Probably a
bad solder joint underneath. I pushed a rubber spacer ( an amp foot) under it. That was seven or
eight years ago and no problems.

Martin Abend · From: Berlin, Germany

Thanks a bunch for your suggestions, gentlemen. I had hoped that I wouldn't have to send it back for service, but I guess that's inevitable now... darn mailorders! Wink

Best,

MArtin

Andy Zynda · From: Wisconsin

I agree with Ken. I had a Pignose GA40 that did this very thing. I rewind transformers, and suspected a loose lamination, or winding, so I sent it to the local motor repair shop to have her dipped in Varnish and baked. (hoped to have the varnish run in, soak the loose area, and harden up)
It was a great idea.
The tranny came back dead. Sad

Today's power trannies have a thermal overload fuse in them, just like blow-dryers. The heat from the oven opened up the fuse and it was game over.
Luckily, I was able to dig into the tranny, locate the fuse (outside the windings and core) bypass it, resealed the transformer, and had it dipped again.
All has been well ever since.
But what a pain.
-andy-

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