[R-390] ER article for R390A SS regulator

[Tisha Hayes]

When the radio was used in RTTY service while being powered from fairly
unstable electric generators it could get drifty enough that the op would
need to be constantly tweaking the frequency on a bank of receivers as line
voltages went up and down. It made perfect sense to stabilize heater
current the BFO and PTO tubes through the use of a ballast tube in series
with the tube filaments.

It may be that most radios that are out there today are not going to be
operating from a small generator in RTTY service. For those applications
maybe it is just fine to use a dropping resistor or another tube filament
in series to just keep the bulbs lit.

The 3FT7 is not a perfect solution; as has been said, it is a fairly
fragile tube that is getting pretty rare and expensive and there are
alternative approaches we can take to further reduce the heat and
electrical load inside of the radio.

Any linear device; like a resistor or an LM series regulator is going to
need to contend with heat dissipation as the voltage drop is going to be
translated in to thermal energy. The difference in voltage between both
sides of the device is the voltage drop, times the current (good 'ol ohms
law) equals electrical watts that is the same as thermal watts.

If you use a very tiny switching converter as the "sigmapert" device made
by Dr. Kurt Schmid the total current goes down because of the conversion in
the supply. The heat dissipation drops down to around 1 watt as the
converter efficiency is 94%. It is not a magical device, it contains a
small commercially made switching regulator with a few other peripheral
components for AC to DC rectification and some caps. It does require an
additional connection to chassis ground; either by attaching a ground lead
to what looks like an anode at the top of the metallic tube shaped device
or by running a ground wire to pin #1 of the tube socket. Pin #1 is not
used by the 3FT7 tube so if you later decide to pull the solid state
converter and put in an old 3FT7 it does not cause a problem.

I have one in my primary R-390A and it has been there for a few years now.
It does not run warm and has been reliable. If I feel any guilt I can
always pop in a 3FT7 as I have a few spares that I am saving as investment
properties to resell to 'yall when the prices climb to $200 each.

*Ms. Tisha Hayes, AA4HA*
*"*There are many who live in the mountains and behave as if they were in **the
town; they are wasting their time.*
* It is possible to be a solitary in one's mind while living in a crowd;
and it is possible for those who are **solitary to live in the crowd of
their own thoughts.*"*
**-Amma Syncletica of Alexandria**