APT Holman amplifier, debug, bias setting 1982

[Jonpaul]

Greetings all,

I am Resuscitating my 3 pcs APT Holman power amps, the usual oxidized relay contacts and discovered an intermittent dual PCB mount RCA jack, resoldered the PCB traces. Works fine.

re the trimpot adjustments, Seeking the recommended procedure to set offset and bias trimpots. Suggest to replace original 1 turn trimpots with multiturn?

First preheat amp at modest load? 10W?

Adj offset to 0 DC out +/- 10...20 mv?

Adj Bias: preset pot for 20 ma quiescent current

Set generator for 1 W output power at 1 kHz?

Use THD analyzer, observe residual THD products.

Trim bias control for lowest zero crossing distortion?

Readjust offset after bias?

Have original user manual, but not service manual.


MANY THANKS

Jon PAUL
Crypto-Museum

 

[kannan_s]

Nice posting on APT Power amp troubleshooting/ setting up in the other thread ( called Undeservedly forgotten .... APT 1 or similar named) in this Forum - please search for APT 1
you will see lot of information on even improving the performance
Kannan

 

[kannan_s]

named
APT 1 power amp – undeservedly forgotten

 

[Jonpaul]

Yes posted to undeserved forgotten thread but seems no activity on that very old thread.

Finally found the service manual tho.

Cheers

Jon