In Reply to: scott 340b (early) tuner fail posted by thermionic emitter on February 1, 2017 at 21:03:56:
The 100 some Volt B+ that is at the plates of the tuner tubes? What does it drop to? Nothing is smoking or smell anything getting hot when it fails? Then probably a bad connection or cracked resistor. Trace the voltage drop in failure mode starting at the PS filter capacitors there are resistors in series starting with R311, R310, R309, R308, R205... if it is the feed marked 5. Add R307, R508 to that if it is the feed marked 4...
What you will probably see is the voltage on one side of one of these resistors and not the other, so bad connection/solder joint. Or one of the resistors is getting hot and something is pulling it down on the other side (less likely).
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Follow Ups
- RE: scott 340b (early) tuner fail - fredtr 05:28:45 02/02/17 (1)
- RE: scott 340b (early) tuner fail - thermionic emitter 11:23:29 02/02/17 (0)