[Amps] 4 x GU-81 Grounded Grid Penthodes

[Ron Youvan]

   Máximo EA1DDO_HK1H wrote:

> I´ve been told that I can use DC for filaments (instead of AC), Is that true?
> If it is true, Can I use switching power supply for filaments?

> Tubes GU81 needs 12.6 v and around 10A, I could use 2 x 12.6 25A switching power supply in parallel with two chokes.

> Is that correct?

> Is there any difference to use AC or DC for filaments?  (in grounded grid )

   You can always use DC on an indirectly heated cathode, but with a directly heated filament you 
must consider the fact that one end of the "cathode" will have 12.6 Volts more or less cathode to 
grid bias than the other, this will cause one half of the filament wire to emit more electrons than 
the other.  Generally this is to be avoided.  It can reduce the life of the filament, as the 
emissive current must be added to the filament current in that part of the filament causing that 
part to operate at a higher (than normal) temperature.
   I do not know if this would be a problem with GU81Ms or not.
It is next to impossible to parallel two switching supplies without having one regulator circuit 
control both supplies, they will not "share" the load without a pair of power loosing combining 
resistors.
-- 
    73 Ron KA4INM - All E-mail sent to this address shall linger in the Google cloud forever!