Very interesting i didn't realize some heaters are run in series. I checked the cold resistance of the 88V heaters and is 126 ohm which divided by 14 heaters makes 9 ohm, about right for a single 6.3 V cold heater.
Factory I don't understand the bulb idea completely. Presently the scope absorbs slightly less than 100W, and the fuses would allow for roughly 200W, it's a 2A fuse. If I put a 100W bulb in series the heaters will not heat up enough but with a 200W bulb a short would blow up the fuse. Should I put a 300 W bulb in series and a larger fuse, like 2 or 4 A?
The reason I am hesitant is that my variac is 110V, following a 220 to 110 transformer and at the moment the power cord current runaway, with all the tubes in, is slow enough that I can turn the variac off before blowing the fuse. Most of the time.
Finding an array of large 110V bulbs in Italy now is out of the question.
Anyway I am making progress, unplugged the N 9 & 10 connectors from the 88 V PS board and got around -160 V, not quite -150 but with no load. Is it already time to trim this supply to its correct voltage?
Tomorrow I'll check the 88 V supply.
