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

[Bill Fuqua]

    I had built regen receivers in the early 60's using 12AT7 and +12 
volts. It worked just fine as
far as I could tell.
   On the other hand, I made an amplifier with 4x 6AG7s pressed into a 
aluminum block for
a heat sink and ran from 800 to 1100 volts on the plates. Was getting 
around 300 Watts plate
input power with a couple Watts drive. Which was not bad for a Grounded 
Grid amplifier. Did
have to condition the tubes by bringing up the HV  slowly and allowing them 
to flash a
couple of times. I still have the heat sink I made. Must try that one again.
It did not work so well above 20 meters however.

73
Bill wa4lav


At 08:14 AM 10/11/2011 -0400, David Stinson wrote:
>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
>
>
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