31-10-2015, 10:10 PM
(31-10-2015, 08:42 AM)AlanBeckett Wrote: I always took 'Directly Heated' to mean no Cathode, ie the Filament is the source of the Electrons.
There can be 'Indirectly Heated'with the Cathode internally connected to one side of the Heater as with many Rectifiers.
Alan
I agree - there are several rectifier valves which are directly heated (eg 5Y3, which is 350V 120mA capability with a 5V heater); indirectly heated but with heater internally connected to cathode (eg 5U4, which is 450V 225mA capability with a 5V heater); and indirectly heated with heater isolated from cathode (eg 6X4, which is 325V 70mA capability with a 6.3V heater).
The idea of an indirectly heated cathode, even though it is internally connected to heater, is so that it will take a while to warm up so the HT capacitors won't charge to a high peak voltage due to the rectifier being active before the other valves in the equipment have warmed up. It's something to bear in mind when replacing valve rectifiers with silicon diodes - check your capacitors!
