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Old 6th September 2014, 02:59 PM
Richard Richard is offline
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Join Date: Dec 2005
Location: Notts
Posts: 5,198
Default Re: KT88 construction problem


Heating of the load resistor shows an AC current is going through it. This may be from an external signal that is being amplified (RF) or an oscillation within the amp circuit itself.

1) Short the inputs with a shorted RCA plug or by attaching a CD player etc. I have had this myself with a Kit88 and yes the resistor gets hot by itself as you find.

2) It may be a bad valve causing oscillation. Swap U2 across channels and see if the problem stays or moves with the valve to the other channel. Swap U3 and U4, for a similar check, and then U1 also.

3) It could be oscillation within the amp itself. Check carefully that the output transformer wires are connected correctly and the feedback wire and components are correctly connected.
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