11-08-2016, 09:04 AM
(11-08-2016, 08:52 AM)signalman4 Wrote: Yes it wouldn't go up to HT because of R19 (1k) which would hold it down a bit.
I did a quick calculation and I reckon the voltage across C21A could rise to about 50 volts or so through half the filament of V4.
There are some HT and screen decoupling caps that could also be at risk because the HT voltage rail would also rise quite a lot.
I think a clamping zener diode of suitable voltage (8.2v or 9v) might be a sensible addition from V4 pin 7 to chassis.
Don't see the point of a zener diode, the electrolytics should be replaced anyways, I make the voltage across C21 with o/c V2 heater as approx 25 volts so 25 volt electrolytic should do.
Lawrence.
