Bass leaves after amp warms up?

The dropout in sound as described seems to fall in line with what one would encounter if one phase of the signal/incoming power feed were to drop out somewhere along the line. Preamp volume control or ac outlet problem possibly? However, I cannot reconcile the fact that it only seems to occur after warmup with my hypothesis.

Ant
When is the electrician coming over?
Best JohnnyR

The speaker cables were already replaced with the same model *audioquest comet biwire

The problem still persists:

I am auditioning different speaker cables tomorrow followed by Electrician to check connections.

I will report back

Thanks to everyone

I substituted Different high end speaker cables today.
What I heard was alot of bass but it wasn't the lower octive & punchy kind which I get from Audioquest.
Is it possible audioquest cables can in the first hour put out a more desirable bass like a subwoofer that is punchy but then "resort" to bass that is less deep or punchy?
Which is unsatisfying to me

Perhaps I need a subwoofer?

But this is perculular:
I put back Audioquest cables using just one speaker & was unable to get the "correct" bass from either side of the amp.
I then tried the other speaker cable from audioquest & the bass was powerful & deep again.
So I don't know what this means

Is it possible audioquest cables can in the first hour put out a more desirable bass like a subwoofer that is punchy but then "resort" to bass that is less deep or punchy?

No, IMO.

I put back Audioquest cables using just one speaker & was unable to get the "correct" bass from either side of the amp. I then tried the other speaker cable from audioquest & the bass was powerful & deep again. So I don't know what this means.

My guess is that something else was changing (perhaps as a result of cooling off somewhat) while you were changing cables. Although you'll want to determine if the different behaviors with the two different cables are repeatable, to cover the possibility that one of the two cables is defective in some manner.

Regards,
-- Al