TBX
TBX-4
TBX-6 RT (Lower right), EL-2 rectifier (Lower Left) and TBX-8 accessory box (rewired for pre-TBX-8 voltage reqts) (top)
This
radio was most famously used in World War II by Marine Raiders and
Native American Navaho “Code Talkers”. Lots of other
brave souls used it too. It was usually carried by four men, one who
carried the R-T, one who carried the accessory box (which is the same
size as the radio), and one who carried the antenna and the last to
carry the hand generator. The hand generator is like an aluminum
basketball. The radio would communicate with a similar radio
installed on a ship. It took operators ten minutes to set up and use
the radio.
I started with a TBX-4 off of Ebay in early 2010. It pays to lurk there, for sure. My TBX-4 certainly isn’t museum grade, but it’s in fair shape. It lacks a cover which would contain frequency charts made especially for this radio. The dials are not graduated in frequency, but just a scale. You look up the desired frequency and set its corresponding number in the scale on the radio. Powering it was a new challenge for me…
Here is my first solution to power the receiver. . I went to the local surplus store (Axman Surplus) and bought battery holders. I then used banana plugs to mate with the power cable, which I had attached to my new box with a hose clamp and some plumbing strap. The box is made out of scrap flooring we had. Pretty crude solution, but it worked.
Ebay to the rescue. This battery box is for a TBX-8, but I rewired it. Works great, and now it holds my other TBX accessories.
The hand-crank generator shown here is another eBay find. It came with one crank and didn’t work. I coaxed it back to life (stuck vibrator) and here it is being tested with a light bulb and the multi-meter (indicating 512V). I fit it with a pulley and can run it with the motor shown- the motor is a pull from a Delta benchtop bandsaw that was found in the alley. It won’t start itself, but once running it works OK. I have since put a belt guard on. Once I get the plug end of the transmitter PS fitted, I’m ready to get on the air.
I’m fairly sure this is an EL-2 Rectifier Power Supply (receive) that is part of TBX-4.
Here it is with the cover off. When I got it, it didn’t work. There filament voltage wouldn’t adjust properly on the radio. I traced it out on the schematic and figured out that it was an issue in the copper oxide rectifier in the rear right of the photo above. I probed the rectifier and figured out that it had a very high resistance across two of the terminals. These rectifiers are literally bolts and washers dipped in chemicals.
I bolted a modern rectifier on the backside of the original. The power supply would have looked a little funny with no rectifier in the corner, so I left it in. This fixed the low voltage issue in the PS. There was also a high voltage issue. I began with the resistive divider and quickly found a resistor whose value had gone high. Since getting the voltages right was mostly cut and try (maybe I as using the wrong formulas to estimate values, but they were always way off what I expected), I wound up with two in series. It seems to work well. I also had to replace the cord and installed a fuse after the PS shocked me a couple of times.
Here’s a photo of the generator (transmit). ½ HP and generates 500VDC, and two 12 VDC sources… One is isolated for the microphone.
See the two handprints inside the top cover of the rectifier power supply above? They’re in the paint and look like a woman’s hand. The history in these radios is amazing.