[ARC5] Low B+: The Genius of A.R.C.

[David Stinson]

Most of you know I've been for years working on ways 
to use our rigs at low B+ to both preserve them and 
to operate them without extensive parts replacement.
Results with receivers have been good.  "ARC-5" receivers 
work well all the way down to 24 volts with external amplifed
speakers.  They have plenty of audio for earphones without the
amplification.  This allows them to be operated with a single
24 volt, 2 amp power supply.  Over the years I've found no 
down-side at all to this mode.  Despite dire warnings of 
"cathode interface," I've had no trouble.

A few years ago, I moved on to working with the transmitters.
I built a milli-watt drive 100 watt amplifier 
and powered an "ARC-5" transmitter from only 24 volts.  
The rig put out a good, stable signal of about 1/4 watt.

Now, since I'm building the 160 mtr AN/ARC-5 rig,
I tried it with the MD-7 modulator.  I jumpered the 
dynamotor connection pins, putting 24 volts B+ on all
the modulator and transmitter stages.  Remarkably,
the scope showed 1/4 watt output of nice, 100% modulated,
good-sounding signal.  
Way more than enough to drive my amplifier.

No way these modulation and transmitter stages continue
to work as intended all the way down to their A+ voltage
levels unless they were thoughtfully, ingeniusly designed 
to do just that.  Try getting a DX-100 to do it ;-).

I think we should find the final resting places of the men
who designed these sets and place a brass placard 
next to their monument stone: "Unsung American Genius."

73 DE Dave AB5S