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Old 8th September 2005, 02:31 PM   #1
liberty is offline liberty  Italy
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Location: Ancona
Default Problem with cathode resistor

I have a single ended amp lo scherzo and it run good since 1998. Now there is a problem in one channel, it doesn't make sound and burn the cathode resistor. I changed the tubes and the resistor but it burnt again. I measured all parts and amp checked good. The question is, what to do?

Thanks a lot for any suggestion.

Lo scherzo
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Old 8th September 2005, 04:49 PM   #2
amperex is offline amperex  United States
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Location: MI
How about a poor tube socket that does not provide good contact to the tube bias pin?
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Old 8th September 2005, 05:29 PM   #3
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Inspect if C3/4 are not leaky and if R15/16 and R9/10 are not open.

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Old 9th September 2005, 01:37 AM   #4
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If the above mentioned components are good, use an AC voltmeter or (preferably) 'scope to look for a nasty HF oscillation. If that's the case, check the PSU caps.
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