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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
garibaldi's avatar
garibaldi OP
12 posts
 
Thanks for all the responses. It's apparent to me that the fix is beyond my capabilities. Therefore, it's going in for repair. It'll take a while for an answer since the unit needs to be shipped. I will post the results of that repair here when I get it back.

Again, thanks for all the responses. I truly appreciate the information that everyone offered.

Regards,
GP
czarivey
5,785 posts
 
From what I saw from pin locations there could be some protection involved and maybe some resistor is blown that provides voltage drop for the offset.
lou_setriodes's avatar
lou_setriodes
673 posts
 
I agree with Bjbcab, that's the only reason why I read this thread :)
czarivey
5,785 posts
 
Lou, b aware that Bj-bcab already sounds wierd!
lou_setriodes's avatar
lou_setriodes
673 posts
 
Be nice Czar, he doesn't have a hyphen in his screen name.
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