[Milsurplus] ARC-5 screen supply

[Dennis Monticelli]

Hi Mack,

I've been reading the threads and I like all the solid state suggestions.  A
simple zener stack with a couple of mils running through them and either a
source or emitter follower transistor will serve you well.  You will need a
transistor (FET or bipolar) with a breakdown voltage of at least 600V.   It
is good practice to place a resistor in the drain (or collector) sized to
drop over the half the voltage being stood off (e.g. 500-200=300V so drop
200V across the resistor and leave about 100V for the transistor).  This
provides current limiting and spreads the heat around.  It will also help
prevent a bipolar transistor from entering "second breakdown" (simultaneous
application of high voltage and high current).

My T-22/ARC-5 is used weekly and I have also found the screen voltage to be
a lever on chirp.  I run the osc continuously (even during receiver periods)
off a stack of two VR tubes totaling 210V and then add a zener to the VR
stack to make 260V which is then buffered by a bipolar emitter follower to
feed the screens.  I still had a small amount of residual chirp so I
ultimately ended up adding plate voltage regulation too but that's a
refinement that may not be worth your trouble.

The way I get away with running the osc even during receive is the freq
pulling that naturally occurs when entering transmit mode.  This means my
osc sig sits 2KHz higher than my IF passband while receiving so I don't have
to listen to it.  Running the osc all the time makes for an ultra stable
signal.

BTW, I put a switch on the power supply that defeats the voltage
regulation.  That way if I want it to sound "authentic" during a particular
operating event like SKN, I just throw the switch.  It gives the rig a split
personality :-)

Dennis AE6C