[ARC5] WTB-Power supply For BC-459

Sat Oct 22 20:16:42 EDT 2016

Hi Tom,

Ken has asked some very good questions.  Most of the Command transmitters
have been modified by the hams of yesteryear.  That often means the
filaments have been changed to 12 volts, the selector relay has been
removed and a female octal socket has been placed on the back to replace
the socket that mates with that in the rack mount.  Are you planning to run
CW or phone?  For phone you will need a modulator.

For power supply, your best bet is a regulated supply such as the Heathkit
PS-4 provided you limit the current to 100 mA max.  With voltage of about
200 to 250, you can run all three B+ requirements, plates, screens and
oscillator, off the same voltage.

I built one power supply and modified another to provide either QRP or QRO.

The  "impoverished experimenter"  QRP supply was a modification of a
recycled small UPS with a second UPS transformer added inside.  That was
originally designed as a poor-man's isolation transformer.  I added a
bridge rectifier, and a pair of 220 uFD caps, a 15 ohm series resistor and
a 100K bleeder, al recycled from a computer power supply.  That provided
165 volts no load and 155 volts under load for all 3 feeds and no chirp.
Filament supply was added using the 16.5 volt secondary for the first UPS
transformer (which is also the primary for the second transformer).  That
was rectified, filtered and fed to an LM-317 on a recycled heat sink.  I
also added a resistor to reduce the voltage a bit before the LM-317.
Output is 12.6 volts DC.

The transmitter puts out about 4.5 to 5 watts into a 50 ohm dummy load.

The second supply for QRO was a Heathkit HP-20 utility supply  to which I
added on-board voltage regulation with two N-channel MOSFets using three
zeners in the gate supply, a pair of 100 volt that actually zenered at 98
volts and a 75 volt.  The result was fed by the 300 volt side of the
Heathkit.  I repurposed the 300 volt point on the output octal socket to
270 and repurposed an unused socket terminal for the 200 volt output.  The
600 volt output was fed to the plates.

Worked great.  The Heath supply also provided filament voltage. The key-up
(no load) plate volts on that supply is 733 and 664 at key down. The 300
volt side was about half that as could be expected.  The 60 watt dummy load
bulb really lit up!

The transmitter's female octal power socket struck me as a dangerous
choice, requiring a male plug with voltage on it. .  I fed color coded
wires out through the octal socket keyway to an octal plug to mate with the
Heathkit.  I also used the same pin configuration on the  "impoverished
experimenter" supply octal output socket that I had added so as to keep the
two supplies plug-compatible.

I did this for two different Command transmitters, an ARC-5 T-22 and a
BC-696A for 40 and  80 meters.

I later built a QSK box consisting af a DPDT and an SPST relay  The two
little relays also recycled from an UPS mimicked the action of the missing
selector relay, allowing for a slight delay in keying and full break-in.
The DPDT relay turns on the oscillator and also powers the second relay
which is the actual keying relay. I mountd this on perf board inside a
cheap plastic single gang box with a metal cover drilled for mounting the
code key jack.

The N-channel MOSFets were recycled from computer power supplies after a
quick look at the spec sheets.  It pays to save some of this stuff.

Since the MOSFets and heat sink were rlatively close to the original
Heathkit chassis-mounted power resistor, I aded a little fan powered by one
of the power supply's 6 volt filament windings rectified by a 1N4007 and
filtered by a little 100 uFD 25 volt electrolytic.  That resulted in a DC
voltage of just under 10 allowing the 12 volt fan to exhaust the heated air
with very little noise

The results of restoring function to the command transmitters and of the
power supplies is written up in detail in the December 2015 and January
2016 issues of THE SPECTRUM MONITOR.

I recommend starting with a QRP approach as a cheap introduction to
operating one of these.

Rich KB8TAD

On Sat, Oct 22, 2016 at 2:18 PM, Kenneth G. Gordon <kgordon2006 at frontier.com
> wrote:

> On 22 Oct 2016 at 13:29, Thomas Scherer wrote:
>
> > Ken,
> >  Not at this time sad to say...
>
> Hmmm....OK.
>
> So, what is your plan? Are you hoping to be able to buy a complete power
> supply for the
> BC-459, with the necessary plug to connect to the rear?
>
> Is the BC-459 modified in any way? (Key jack, internal mods, replaced rear
> connector, etc.)
>
> What had you planned to use for a receiver?
>
> Just curious....
>
> Ken W7EKB
>
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