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Amplifier problem

Please help:

I have a problem with my amplifier - one resistor (R47) got loose, the technician soldered it, all tubes are working, I can hear the music, but in a 3-5 minutes there is a buzzing (or, rather, scratching) sound from the right speaker, after which I switch the amp off.

Before the damage, the amp cooled down rather quickly (after 5-10 minutes all KT88 tubes were cool), and now only one output tube gets coolo quickly, while others remain hot for approx. 20 - 30 minutes (like in Cary SLI-80). All fuses are OK. The amp is Unison Research Sinfonia.

I tried other quads, but in approx. 3-5 minutes of operation one of them became hot red in the plate. The technicial could not identify the problem. I reported the situation to the manufacturer, but so far did not receive a reply.

I will appreciate all recommendations.
transl

Showing 1 response by pauly

pauly
1,012 posts
 
If one resistor worked itself loose, it is quite like that you have shoddy soldering throughout your amp and few other things got may work themselves loose.

The fact that your tubes are not cooling off is a bit strange and I can only think a bleeder resistor has also come loose. High value resistors are commonly used in most circuits to bleeds the caps of their voltage after you switch off, although I have never seen them used in the filament circuitry before.

The scratchy sound could be a tube with dirty pins. Swap you tubes around (left channel to right) and see if the scratch moves to the other channel.

Regards
Paul
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