Posted By: Robert Nickels (W9RAN) Posted: 07/203/2022 On the workbench 0 Comments 07/203/2022 |
The "Art" of HomebrewingWB6NVH's two-piece portable |
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Homebrewing has always been a big part of ham radio, but it clearly peaked during the period following WWII when surplus components became availalbe in quantity and at low prices. Most large cities had at least one surplus store and the supply was so great that authors wrote magazine articles based around surplus components because they knew readers would have no problem in finding them. But other builders went their own way, no doubt borrowing ideas from others and from handbooks and other publications. Such seems to be the case for the two-piece portable 80-40 meter CW field radio that was a hamfest find for collector and restorer Geoff Fors, WB6NVH. Here's how he describes it: The two-chest rig is 80/40 Meters. The transmitter uses a 6L6 in the PA and I forget what it uses as the osc. or the IPA. I was surprised, as I said, that it has a Western Electric mercury wetted relay for keying. Surprised and somewhat non-plussed as to why it would have that. That is going to a lot of trouble. The transmitter runs off 12 Volts and uses a transistor inverter for B+, the transistors are early 1960's Germanium power types which help to date it as perhaps 1963-64. As mentioned, the transmitter has no provision for crystal control, it is VFO only.
The receiver has a crystal calibrator but not what you would expect. It has a crystal for 3500 kHz and when on, places a nice band edge marker on 3500 and the harmonic 7000 kHz. I knew I had seen those IF transformers somewhere and it took awhile but eventually I found they are from an/ARN-7 RDF aircraft receiver. I forget what IF frequency those were, other than it isn't 455 kHz. 185 or 85 something like that (?)
These wooden chest radios are perhaps one of the neatest things I have ever bought at a hamfest. I looked at them and didn't buy them at first, I think the seller wanted $ 75 for them. Seller was one of these non-ham estate sale pickers we get over here. This was at the now defunct DeAnza College Electronics Flea Market in Silicon Valley about 8 years ago. The following month the seller was back and so were these, still unsold, at a reduced price. I think I may have taken a gamble and paid $ 50 for them, it was no more than that. Since then I have had so much pleasure from them that I would have paid far more had I known. I got some paint color matched and patched and repainted the chests. They haven't needed any other work. Receiver performance is excellent and I have detected no drift, informally. Tuning with the National vernier is smooth and pleasant. The receiver originally ran off of a 1.5 Volt A battery and two 22.5V B batteries in series for 45V B+, with a pair of C cells in series for the bias. The A battery is that one which looks like a 6 Volt spring contact lantern battery, except at 1.5V. In my opinion the filament draw makes that battery a bad choice as it won't last too long. I presently use a set of small lab type regulated supplies to run it temporarily.
When I got it, there was a cloth bag full of accessory items in it including a number of pilot lamp bulbs soldered to lengths of wire with alligator clips. This was a way of tuning the antenna pre-dating widespread use of the SWR bridge and is supposed to be quite accurate.
A quality homebrew job like this offers real insight into not just the person who designed and built it, but the state of the ham radio hobby at the time. Even at surplus prices, given that the builder probably had a full-time job it's hard to imagine that his motivation was just to save money - he was out to make a portable set that did exactly what HE wanted. He selected higher quality components to get the payoff in stability that Geoff observed even now, decades later. It would have been easier to use a vibrator power supply but the builder clearly went for the modern (at the time) inverter approach to get higher efficiency.
One can only guess at how many Field Days or just afternoons at the picnic table these radios have been toted to, and how many contacts were made with them. Thanks to Geoff for sharing this example of homebrewing at the peak of the art.
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