In article .com,
wrote:
I have a background in electronics but not in audio amplifier.
I have a Sony Audio amplifier, a 25 years old model. I turn on the
power and it takes 20 to 40 minutes to hear the music. Just before I
hear the music, There is a ZZZZZZZZZZZZZ then a CLICK. Each selection
(Tuner, Aux or Tape) works or does not. Once the amp works, it works
until I turn it off.

Sounds like the speakers are fed via a relay - commonly to prevent a thump
in the speakers at power up time. There will be a timing circuit
associated with it. May be even they trip out if there's a large DC offset
through the amp.

--
*You can't teach an old mouse new clicks *

Dave Plowman London SW
To e-mail, change noise into sound.