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Old 6th September 2014, 06:12 PM
John Caswell John Caswell is offline
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Join Date: Dec 2005
Location: Wokingham, Berkshire
Posts: 1,698
Default Re: KT88 construction problem

Hi,
With the amplifier turned off and the KT88s removed measure from Pin 5 of each KT88 to earth. Should read 220K or thereabouts. If not you have a wiring fault. Correct this and try again.
If you still have a problem disconnect the feedback link to C10/R18 on the faulty channel, if the problem goes away then the phase of the feedback is wrong and can be corrected in one of several ways. IF you are sure that you have wired the secondary of the output tx correctly then it is possible that you have the primary wired incorrectly or the two anodes feeds of the 5687 driver "**** about face" In which case swap one or the other reconnect feedback and try again. I would choose the 5687 anode feeds as the simplest method
The variations on U2 I suggest are within limits of 10%.
Let us know how you get on.
Have you spoken to Matthew about this? as I am involved indirectly

John
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