My Adcom preamp Model 450,shut off by itself?

SOURCE: No output in Right channel on my Adcom preamp GTP-450

Hi...
Have you tried swapping speakers to see if the trouble moves to the other speaker?
It could be a dirty selector switch .

It could be a broken solder contact on the input or output RCA jacks

SOURCE: Adcom 7500, Adcom 5400(bi-amp), Marantz AV-9000, Dakiom HA103

Try just the power amp on ..nothing connected
no Dakiom thingy either. It's a matter of elimination. Start at the output device and work back. Keep the Dakiom out of the loop.
If there's hum with just the Adcom..then it's the ADCOM

SOURCE: Help! My Adcom 555 amp and Adcom preamp is making

Try a different audio source.

Disconnect the cable at the preamp end from the amp and see if it stops.

If it does = preamp.

If not = cable or amp.

Reseat cables at both ends with a twisting motion.

Swap left to right.

There is a good chance that a common control may have developed a high-resistance or 'dead' spot through idleness and is causing your symptom. Turn the POWER OFF and operate every control throughout its range a number of times, especially rarely-used ones like Tape Monitors and the Mute control.

Turn the volume to something reasonable and see if that helped.

Lots of ways to eliminate sources of the fault and isolate the problem.