[morzh]

Well, I decided to put the case back and leave it for a while; I spoke to a friend of mine while running in and monitoring the signal when after about 40 minutes I started noticing a distortion which manifested itself as one slope being much faster and one top looking a bit flattish.
I cooled it off, it started normally and then progressed to flattening one top again;
Changing the output tubes (they are followers) resulted in reversal of the flattened peaks.

I thought of maybe buying another 6AU5GT tube but both tested at leat twice the value shown in the chart (one required me to go to 15000 scale whereas the value should be about 2,900 for new tube).

In any case I decided to check voltages and I noticed the voltage is low, being 120V whereit calles for 190V (B+), and input being 160V whereas it says it should be 215V (the first filter cap). The ripple looks reasonable.

Also plate voltage at the output should be 165V and at 110VAC input it is 85V, at 120VAC it is 95V.

Then I looked at the sch and noticed this: the sch calls for 5AR4 tube for the rectifier.
The actually installed tube is 5Y3GT.
But the marking on the actual chassis for V5 tube is also 5Y3GT.

I know 5AR4 is about 40% more current capable tube with less resistance and indirect heated cathode, so in part the low voltage could be explained by it, but then obviously they did use 5Y3 tube if it is printed on the chassis.

This is interesting. Anyone has experience with HPs and their performance?
I could leave it the way it is but somehow I think I want to straighten this out.