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Monday, April 18, 2016

Wooden Boats, VFOs and PTOs -- Recovering Lost Arts

1 comment:

  1. There were construction articles in the sixties for PTOs, in "QSR" and "73". They are mechanically intensive, but in this age of frequency readouts, a lot less fuss needs to be made about linearity. It gives multiple turns, and no variable capacitor.

    In 1974, there was an article in "Ham Radio" about locking a 50MHz VCO to a broadcast band variable oscillator. In this case, he used the PTO mechanism from a car radio, an eat way to take care of the mechanics. At the time, the local surplus place was selling the mechanisms for about a dollar. Of course, now the car radios tuned that way are well in the past, digital tuning taking over, so no longer easy to find those mechanisms.

    And yes, it's easy to put an FET in those Collins PTOs. About 1974 I got a few 1-1.5MHz Collins PTOs for cheap at a hamfest. I soldered an FET to the tube socket, maybe changed the plate resistor to a lower value, and ran it off a much lower voltage. All was fine, the oscillator was simple, it was the mechanism that was complicated.



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