K8leewmm wrote.
>> Gentlemen
>> driving to a friends qth tomorrow to look at his 425 amp.
>> He says that the "overdrive" lamps comes on with little or nearly no
drive
>> Ideas?
Do check the HV filter capacitors which will are very suspect by this age of
amp. I've found that when they fail, the overdrive light comes on with just
a few watts of drive but not with the normal intensity - I suspect this may
be related to the HV supply being deeply modulated with 100/120 Hz. In fact
this symptom, combined with indicated HV about 25% down on normal (taking
into account that the HV display will probably be lower than when the amp
was new due to dropper resistor aging), has always been a sure sign of
failed filter caps in the many 425s I've had to deal with.
If they are at fault, don't forget to replace the HV bleeder resistors with
modern carbon / metal film ones at the same time.
73,
Andy, G4PIQ
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