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Motorboating after tube change

I posted this on Audioasylum tubes, but I'd like to increase the knowledge base, so here I am.

I own an Aikido preamp that was built for me in 2007. Since I don't use it that much, I haven't replace the tubes till now. After I changed them out, there was clearly audible motorboating emanating from both speakers. I returned each old tube to the unit but the motorboating didn't stop. The only screwup was that when initially replacing the tubes, I accidentally installed a 5751 into the spot for a 5755.

Any ideas?

Thx,

GP
128x128garibaldi
atmasphere's avatar
atmasphere
11,793 posts
 
Motorboating is an indication of a power supply problem.

My theory is that the different tube somehow was able to do some damage, but it is not obvious how upon looking up the two different tubes. So it could be coincidence, but at any rate you are experiencing a power supply problem.
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garibaldi's avatar
garibaldi OP
12 posts
 
Thanks, Guys.

Based on your responses and those on AA, I have a coincidence on my hands. Hard to believe, but there it is. Thanks for diagnosing this over the interwebs.

GP
elevick
2,636 posts
 
I had a bad internal ground which caused motorboating. It was causing a cap to overload. The cap was fine after the ground was fixed.
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