Kenwood KA-5040R: Bias current

[hiwiho]

Dear diyers,

i'm fixing the typical failures in a 1991 Kenwood KA-5040R right now. I want to use it for my second set of equipment.

Changing the leaky electrolytes Elna "for audio", washing the carrier board. I have a copy of the schematic, but the page containing the bias adjustment is missing.

Can anyone tell me the bias adjustment procedure with this amp? The pots in both channels differ visually at least 25%, thats why i think there's something to be done ...

Any help is really appreciated!
Matthias

 

[ostripper]

CP1 or CP3 (emitter resistor blocks) , place your meter across
one half of one of them (single .22 ohm resistor) , you should read 22mv for 100ma or 11mv for 50ma.
your kenwood looks like a standard japanese class AB,so
most AB's I've seen, repaired ,or built use 25-100ma bias
per device.

If you have a scope , you can see little bumps at 0 volts
(switching distortion) if bias is too low. with the bias too high
you could cook eggs on your heatsinks.

Be careful, after changing bias let amp run (warm up) for
awhile, check Mvolt's again. all done..🙂

P.S. service manual should list recommended idle current
(MV or MA).

 

[hiwiho]

Thank you very much, ostripper 🙂

Matthias