29-06-2020, 07:09 AM
(28-06-2020, 07:33 PM)ppppenguin Wrote: The heater cathode insulation of the EZ81 (and EZ80) is good enough for the heater to be at 0V and share its supply with other valves.
This happens to be a Mazda data sheet but the Mullard one is the same: http://tdsl.duncanamps.com/pdf/ez81.pdf
In the unlikely case of using the EZ81 with more than 500V on the cathode then it would need a separate heater winding. But you'd be overrunning the valve anyway.
So something else got connected wrong. I suppose the Philips chassis I had with a separate 6.3V was because they'd always done it that way, or maybe originally used something with a lower or no isolation.
