Last week, I had a completely disturbed stereo-image, as there was a extreme left-right accentuation.
One part of the voice was extreme left, the other extreme right..... A phase splitter failing?
I removed the three 12AU7 (6189W Philips JAN) tubes and changed them by a new same JAN 6189W in middle position
end two ECC82 Philips NOS on each side ..... all was well again.
I am using a 5U4 GB rectifier (Sylvania NOS - USA made) that (normally) has a clear top on the glass, allowing one to see clearly
two glows through the top of the tube;
In about 48 hours, the 5U4 GB started to form a dark marking on the top of the tube, now it has the same mirrorlike
dark top, a bit dull gray from, the inside, but perfectly mirror looked fromtop/down (same as on KT-120)
While the tube makes this change, I am wondering :
- what is this phenomenon?
- what is causing it ? Is it dangerous or just a vaporising of mercury ?
- should I take precautions ? Change the tube ?
With all this going on, the amp keeps playing a top musical performance. Biasing is correct at 0.52 VDC for every tube with nothing drifting off...
Could anyone explain?