To clarify, you cannot make a useful measurement on a working stock Eros, because the servo bias will correct the plate voltage to 100v. You have to convert to the LED and then measure the plate voltage, and try another tube if it is off. I think you want between 95 and 105v at the cathode - it's pretty tight.
The really important measurement is the difference between the 6922 cathode and plate. It should be between 60v and 80v, so that this triode has adequate bias and headroom.
There is a fair amount of DC feedback from the 6922 cathode to the EF86 screen grid, which was intended to keep the parameters close enough. Works for the classic EF86, at least most of them, but it's not enough for the modern variants. I think we did try a few others along with the EH.
Basically, if you can't afford to throw away an expensive NOS EF86 now and then, you should not make this modification. Stressing about the tubes and their cost detracts from the listening experience!
Incidentally, I don't know why there is this difference. I suspect it may be differences in the metallurgy (contact potential) of the grid and cathode materials, since the dimensions of the parts are set by the machinery, and the modern reproductions pretty often use the same machines.
Incidentally, I have found big differences in 6922/6DJ8/7308/6C23Pi grid current vs. voltage, which affects the minimum bias needed on that tube. The 6DJ8s have the greatest problem, so I suggest you avoid that particular variant - the Eros is designed around the 6922, and the Repro high end preamp assumes you have found some good 7308s.
