A Queen can grow old, but she remains a Queen, so her crown has to shine. So, thanks to an unusually warm January Sunday, I decided to bring out, for an in-depth cleaning, the RT-70/GRC I recently bought at a hamvention. Surplus and boatanchors lovers will well know this unit. It puts out 0.5 Watts from 47 to 58,7 MHz, in FM mode. Built at the beginning of the fifties in the US (but several NATO Countries saw contractors versions, like in Italy), the RT-70/GRC was used as a component of several radio-systems: field set PRC-16 with battery-box CY-590/GRC, vehicular set VRC-7 with AM-65/GRC, or as a part of larger radio systems GRC-3 to GRC-8. The RT-70A/GRC variant has a different filament-circuit. Wanting to bring this transceiver to a war era, it has to be said it found its role during the Korean conflict.
Once I brought RT-70 and AF amplifier AM-65 out, and separated them (they’re locked vertically, transceiver on top), removing also the solid bridge connector between the two units, I realized the set was really in good shape, but its main problem was powder. So, with a brush, I removed it as carefully as I could. Then, after it found back its vivid color, I degreased the two front panels, and writings were brilliant again. Working on this part, I noticed a red square stamp, with the “July 1952 MFP” mention. This allows a better age determination of the set.
After cleaning was over, re-assembling started. I love the “solid” feeling of those units. While plugging a connector, or operating commands, you know if you’re acting right: it’s impossible to go wrong, as it simply wouldn’t “feel” right at your fingers! In minutes, the radio was back on the shelf, looking as ready as ever to go on the air. Being valve technology, RT-70 need some attention in supplying power. The set uses 6V heaters and 90V plate power, and it can be powered from vehicle battery using PP-281/GRC (for 12 V), or PP-282/GRC (for 24 V) multivibrator module in the AM-65/GRC power supply / audio amplifier cabinet.
My choice, being a fixed installation, obviously felt on the latter option. Luckily enough, at a previous hamvention, I had bought (originally for a Clansman set, but then I found spare batteries, so it was lying unused) a 24V 4A stabilized power supply. Time to hook cables, to plug the handset, to connect an external antenna (the VHF GSA Clansman kit), and to select “RT-70″ on the AM-65 main switch. White noise was heard…
50.500 MHz (the local meeting frequency for us, surplus lovers), and calling. IX1VKK did answer. He’s not that far from me, around 1 kilometer, so signal was reciprocally good. However, what really caught my attention is the “warmth” of the audio dynamics, both on reception and, judging by what my correspondent told me, on transmission. You can judge for yourself, thanks to this clip:
During the following days, I had QSOs also with stations at a higher distance. My 0.5 Watt covered an abundant 3 kilometers distance. What’s amazing, however, is to use a 20 kilograms set to put out a QRP power. It’s something you can understand and enjoy only if you’re into green radios. Most of all, however, I couldn’t keep myself from a recurring question: in seventy years, will my Degen DE1103 light up at first, just after supplying some power?
73 de Chris