[Amps] D.C. on filaments of GS-35B?

[Jim Thomson]

Date: Wed, 4 Feb 2015 11:00:58 +0000
From: Nuno Lopes <ct2iry at gmail.com>
To: Chris Wilson <chris at chriswilson.tv>
Cc: amps at contesting.com
Subject: Re: [Amps] D.C. on filaments of GS-35B?

Morning Chris,

I know Dominic is using Vdc on the filament, so other guys in France are
using those power supply or PC power supply to feed filament and relays ,
that's the reason that I was asking.

Any special care when feeding with Vdc?

##  The real trick is that you need to return the cathode current back to the cathode. 
The normal deal with a xfmr is to use a fil xfmr with a  CT in the secondary.  The
B-  from the hv supply 1st flows to the neg side of the plate current meter.   Neg side
of grid meter is bonded to chassis.   ¨Positive of both grid + plate meter are tied together,
and then routed through the normal 50k cut off resistor, then through the bias..then to the
CT of the fil xfmr sec.    From there its off to the fil  / cathode.   B+ of course goes to the
anode...completing the loop. 

##  IF  dc is used from say a switching supply,  you still have the requirement to get the
dc cathode current back to the cathode.    And that doesn’t mean tying it to one side of the
fil either. 

Jim    VE7RF