GRC-109 / GRC-9 Battery Operated Power Supplies

UPDATED 2/9/17

Both the GRC-9 and GRC-109 used the BA-48 battery to power their respective receivers as an option.  When operated from the various dynamotor, vibrator or AC supplies, the receivers were also powered continuously.  However, when operating in the field from the G-43 or GN-58 hand-cranked generators, a receiver battery became very handy.

Starting with the receiver power supply:

When keeping a well-disciplined Net schedule, the hand cranked generator powering both the receiver and transmitter might have been remotely practical, but in guarding an Alert Net or other continuous receive requirement in the field, the BA-48 battery was essential.

Above: The BA-48 battery. Note the date code of May 1984

Since a fresh BA-48 is currently unobtanium and since I do a lot of operating of these radios in the field (often by myself) a continuous power supply for the receivers was needed.  So I designed a compact DC-DC converter that provides 100 VDC and 1.4 VDC (regulated) from an external 12 volt battery.  This could either be a vehicle battery or more commonly, a 12 volt Gel Cell. I chose to regulate the 1.4 VDC filament supply to protect the tubes from Murphy’s Law, making it “soldier proof”.

The first GRC-9 prototype supply (gold box) provided power to a 4-contact female cable plug (gray cable, seen above) that mated with the receiver battery connector of the GRC-9 Transmitter-Receiver.  It works great and is very quiet, running at approximately 20 KHz, no mechanical, acoustic or electrical noise is evident.

It uses a custom – designed ferrite core transformer with separate secondaries for each voltage and it draws about 500 ma during receive.  (The GRC-9 prototype power supply was designed to be powered primarily by a 12 Volt vehicle battery so design simplifications were made at the expense of efficiency.)  I later decided to add a capability to allow it to power the GRC-109 receiver as well, but as usual, a custom connector was needed.  The 4-pin battery connector in the GRC-9 and GRC-109 receive systems are unique to those radio as far as I can tell.  What to do?

So I built up a prototype connector and attached it to the power supply so the ‘109 receiver could plug into it directly, just like the BA-48.  I made the female connector from a 1/2 inch white PVC pipe end-cap for a housing and used 4 “molex” – type female sockets from  Radio Shack connectors (R/S Part Number 274-154.  Note: The R/S catalog mis-identifies these sockets as 0.093 inches – they are actually 0.125 inches!).  These are made for 0.125 inch OD pins, the exact size as the ‘109 receiver power pins.

I positioned the females inside the pipe cap using the receiver male plug as an exact alignment positioner.  I then filled the connector with “hot glue” from a glue gun, squirting the molten glue inside via two access holes in the pipe cap.  The solidified glue holds the 4 sockets firmly in place and the pipe cap is attached to the PS cover with a #8 machine screw.  The leads penetrate the cap and cover through a small access hole.  The connector is very rugged, water tight and should be good for several kilovolts insulation-wise.

Above: The completed connector is very rugged and should be even stronger than the rubber-insulated female connectors provided for in the stock system.

The power supply should run the receiver for several days of casual ops in the field on a 7 Amp-Hour Gel Cell. That battery can easily be recharged by a small “dashboard-type” solar panel sold to keep vehicle batteries topped off while I’m doing other stuff at camp. We’re talking indefinite ops here. Next project: maybe build this system into a BA-48 replica.  Then, a similar design as the Nems Clarke 12 Volt “Power Adapter PA-109” for the entire GRC-109 system so I don’t have to crank and send CW at the same time.

The power supply powers the receiver while the PU-181 powers the transmitter. In a quiet location like this, inverter “hash” would be obvious. Nothing heard!

Transmitter HV B+ power supply design  (10-28-12)  Work-in-progress…..

Just starting on a power supply design to provide about 425 – 450 VDC at 100 ma to power both the GRC-109, RS-1 and RS-6 transmitters. For now, I’m concentrating on only the B+ requirements, the TX filament supply to follow.  This supply will be run from a 12 Volt lead acid “garden tractor” battery with much more “camping” lifetime in the field than the Gel Cell currently powering just the receiver.

When complete, the intent is to integrate both the TX and the previously-built RX supply design into a common circuit using this single ferrite core transformer. The following work done on my PS test bed fixture with HV dummy load resistors.

Initial bread board prototype on my PS Test Bed.

Above: So far so good on initial power-up. Delivers about 415 VDC from a 13.6 VDC input. Efficiency = 68%.  Not real great efficiency, but getting there as I learn the Black Art of high frequency ferrite transformer design.  Needs a few more secondary turns too.  Output Ripple less than 0.25%. The scope shows the Base drive and Collector waveforms.  Pretty clean. The 3 big black resistors mounted on the aluminum plate are the HV dummy load resistors simulating the transmitters’ B+ load.

Lots more to do, but I think I will package the integrated TX and RX supply into a spare GRC-109 transmitter case that will power the GRC-109 and RS-1 sets in the field.  It could also power the RS-6 sets as soon as I can figure out those connector issues. A switched tap to provide 580 VDC for the GRC-9 transmitter would also be simple, I designed-in plenty of primary drive power capacity to handle it.  Or maybe a separate GRC-9 TX power supply inside. Stay tuned.

Above: Anyone remember Heathkits? “Learn by doing”.  This is a “build from scratch” using mostly Junk-Box parts on hand…..

Above: Shake the junk-box and see what falls out. Scrap aluminum panel, figure out where all the parts will fit the best, drill a bunch of holes. All the transmitter power supply parts mount to the front panel, the receiver P/S mounts to the case.

The panel came out reasonably well; the parts didn’t take up too much volume in the surplus GRC-109 transmitter case. I applied some sexy Black Satin paint and added a “Made in USA” label. (Well there goes my plausible deniability!) I have to get some plastic caps for those TO-3 transistors, the cases are the Collectors and carry the primary square wave.

Those holes in the corners are for the threaded thumb screws used to attach the stock-issue environmental cover plates, just like the rest of the system components. The DC power wires with Power Pole 30 amp connectors roll up inside the cover. Ready for burial in the swamp.

Above: Design and fabrication complete, testing underway, it’s On the Air, it works great! I included a small fan for forced-air cooling which I might need if I include a GRC-9 transmitter power supply inside in the future. (If I can find a female chassis connector for one!). Just powering the GRC-109 the supply runs barely warm to the touch.

The only significant heat source is the wire wound dropping resistor for the 6.3 volt DC (despite the 6.3 VAC error on the below schematic) transmitter filaments. I couldn’t quickly come up with a simpler, more efficient method for powering them without the heat loss.

The receiver power supply is electrically very quiet. The transmitter supply is also quiet in the receiver above 5 MC or so, but some switching harmonics can be weakly heard in the receiver down on 80 meters with the TX supply running. Need to review the component grounding scheme. Otherwise, so far, so good.

Load and Line regulation is good, with 12.6 VDC input although it is a linear circuit except for the receiver filament source. It draws about 800 ma with just the receiver section turned on, about 4.8 amps with both sections turned on and the transmitter “key down”.

The GRC-109 connectors are made from PVC 3/4 inch threaded pipe adapters with stock Molex female pins held in place with hot glue. Bullet proof, simple, not real pretty. The former stand-alone receiver power module is now installed inside to power both the GRC-9 and GRC-109 receivers.

Now, some systems test and then off to The Bush for a shakedown cruise.

Above: The converter can power both the transmitter and receiver with a small Gel Cell like this but it’s best to power the transmitter directly off the G-43 hand cranked generator and use the Gel Cell for the receiver only. The Gel Cell will run both just fine, but not for a lot of transmission time of course. Better use the garden tractor battery and leave the G-43 at home. That would power everything for a week.

I’ll include the schematics once I am satisfied I don’t need to tweak the design. However, the high voltage supplies are built around ferrite cores that I happened to have in the Junk Box, pedigree unknown, so it may be difficult to replicate. The magnetics are the heart of the design, otherwise just standard HVPS design with regulated +1.4 VDC for the receiver filaments. As a consequence, this post is more about “what can be done” versus a detailed “how to do it”.

UPDATE: So here’s the current prototype schematic which may have morphed a bit along the way. It could be used as a starting point for anyone who may want a similar piece of equipment. I need to get some CADD drawing software,

As with any “One Of” designs, many compromises were made to utilize parts and space available. Component ratings, wire gauge, transformer design, safety factors etc were driven by space and junk-box part realities. Since my application included the availability of a large 12 volt battery for primary power, I was able to keep it simple at the expense of some efficiency.

To improve efficiency I could have used base drive windings for the receiver HV oscillator transistors rather than the simple resistor drive shown. I could have also designed a more efficient 6.3 VDC source for the transmitter filaments rather than the big wire-wound DC dropping resistors shown. Magnetics also determined the oscillation frequency which is 8-9 kc, basically outside my (current!) hearing range. Reducing that frequency would have resulted in somewhat improved efficiency but that would have required better filtering. A tradeoff.

The supply runs fairly cool so that little re-purposed CPU fan is really unnecessary but I included it for a future upgrade to include a transmitter B+ supply for the GRC-9 set. Then additional cooling might be needed. We’ll see.

The receiver supply which was previously built is now mounted inside the box along with the other circuitry. It is inside the shielded box mounted to the case.
Finally got some TO-3 insulating caps for the panel transistors.

Then on to another successful field deployments: ARRL Field Day 2018

I love the sound of CW in the mountains…..