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Old 8th Jul 2019, 12:47 pm   #28
Station X
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Join Date: Jan 2003
Location: Ipswich, Suffolk, IP4, UK.
Posts: 16,570
Default Re: Hacker GP42 and AL42 restoration help

The OP has stated that he only wants to change components which are faulty rather than doing a blanket change. A good idea in my opinion.

He has submitted voltage readings and my only comment about these is the differing voltages on the cathodes of the triode sections of the valves. The 2.2k cathode resistors may have changed value, as might the 220k anode resistors, something easily checked with a meter on resistance range. In fact a check on all resistors to find any which are out of tolerance would be a good idea.

Capacitors are harder to test, but a check to make sure there's no positive voltage on the control grids (pin 8) of the pentodes would be in order. A voltage here would indicate electrically leaky coupling caps C6 and C7.

I would also bear in mind Michael Maurice's knowledge based comments.
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