Restoring a 1940 Thordarson AM/CW Transmitter

The Thordarson 100 watt transmitter was originally designed to be a tri-band switchable AM/CW transmitter. The chassis and panels could be bought from Thordarson pre-punched. The rest of the parts were bought from parts houses. The original design RF tube lineup was 6L6G crystal oscillator, 6L6G doubler and a TZ40 final. The Modulator deck was a 6J7, 6F5, 6F6 driving push-pull 6L6Gs as modulator. This design was was straight forward and reliable.

When I, K5CF, received this transmitter, it was very dirty, rusty and the modulator plate meter was missing. It used to belong to Louie D. McMurray, WA5MDK of Plainview, TX and was given by his son to Ed Mickle, KE5OB, Midland, TX. Ed in turn passed it on to me. It reflects some changes from the original Thordarson design. This particular one uses a 6J5 pierce oscillator, 807 buffer/doubler and an 811A final with plug-in coils rather than a coil turret.

I cleaned it using Naval Jelly on the rust spots and a lot of scrubbing with damp cloths and Q-tips. I then spray painted the rust spots and the cabinet, replaced the rusty hardware and installed a 300MA meter in the modulator. The insulation on the wiring to the RF meter switches is fragil, so I just laced the wires into a cable. The left hand knob on the RF panel ended being just a dummy.

I now use it primarily in the AWA OT CW contest. It works great either crystal or vfo controlled.

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