Ok, here we go with some updated and pictures.
I opened it again and I found that:
1) channel A and B pots are both log pots but they have different values (also after cleaning and drying): A measures now 9.97K and B measures 8.7K...yes, they ARE different...
This "issue" has an easy workaround: set channel A level a little higher...in this way channels sounds very close and past halfway the slight difference tends to zero as soon as max level is reached.
I will change both pots with 10K log new ones (identical).
2) on/off switch has been replaced and it works...but look at its picture how they fixed from the inside...
I will replace it...
3) IN and OUT jack connectors will be replaced as well (INs have broken plastic threads)
4) the tranny seems original and that low "hum" is just normal transformer "noise". If I remove bottom cover, this "hum" is very, very low...and it gest "a little worse" when I put the cover in place and screw it to the chassis...it just transmits tranny vibrations to the chassis...
I fixed this with some strips of adhesive paper tape between bottom cover and chassis edges and this made the trick: now I just can hear the normal tranny "hum" without any additional vibration!
By the way, it looks the correct one:
http://adadepot.com/mods/ADA-B200S-schematics/ADA-B200S-transformer-220V-50hz.pdfI post some pictures just to see if someone (MJMP???
) can identify this unit and see if it's a kind of export item...
It looks like having the chassis of a US unit where they put a 220VAC transformer and a different fuse, removing the white socket (for what was it used on US models???) and replacing it with a black rubber stopper.
@MJMP: can you date this unit from its serial number? Are jack connectors pictures OK? Can you see them right?
By the way, aside from a couple of minor issues that are normal with such used items, this is a great SS power amp.
A very good companion for and a perfect match with the MP-1.
Dead silent even at max levels, reliable, punchy, warm, transparent, thick as a brick and powerful.
I like it with my 2x12 Blackstar cab and I love how it sounds even at very low volume in night time.
Thanks to rnolan and Dante for pushing me down the hill!!!