Tube rolling in Cayin A-88T

I switched the pre-amp tubes, left with right, to check if it was a bad tube, so far no more THUMPs or HUMMM, knock on wood...

It arrived back to the vendor, the pre tubes where malfunctioning, he replaced them with premium units, says the amplifier sounds great now, wants to ship it back...

No thanks, I have no warranty it wont happen again, and it costs almost 200 euros one way shipping...

I always read that amplifiers shouldnt be connected to mains filters, but, as the Cayin only uses 280 watts, I connected it to my ESE labs Balanced isolation transformer...

Well, it did almost the same it did to the TEAC, smoother highs, more body, darker background...

Its getting there, and no more THUMPs or HUMMM yet...

Tubes are not for me, no patience for HUMMM, and THUMP, and adjusting bias, and not so good sound, so it is packed and will be returned today...

I just got one Cayin A-88T, unbelievably it sounds a bit harsh compared with my TEAC DR-L700, a tube amp !!!

Should I use supports with it, or is it unecessary ?

A Tripath TEAC sounds very good with my 96 db speakers, better than the Cayin so far...

I changed to the 8 ohm terminals, and the sound improved a lot, still a bit bright with some recordings, but acceptable now...

I guess some more playing will make it fine...

But I am worried with a THUMP on the left speaker when I switch off, only sometimes, and loud HUMMM, also from the left speaker, and also only a few times, when I turn it on, it stops after a while...

Thanks for your help...