[Amps] Switching Power Supplies

[David Smith]

> 
>  I can't imagine why an amateur would want to use a 
> switching supply for a filament. What reason is there to do 
> that?

I use a switching supply to run the filament of a GS35b in a 70cm amp 
for several reasons:

1. The filament volts should be backed off a little to allow for 
additional heating due to back-bombardment.  The switcher has a pot for 
voltage adjustment - easy!

2. The switcher is regulated - good for field days when the genny is 
wandering a little and you've set the volts "just so", as per (1).

3. The switcher is current limited, reducing the current surge at switch 
-on.  Check the surge current that a nice, low-impedance toroidal 
transformer is capable of delivering to a cold filament and you might be 
rather shocked.

Regards,
Dave
VK3HZ