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I'm restoring a 50s vintage EICO 720 transmitter.
I'm in need of a 50 k potentiometer rated at 4 watts (or above) that is NOT wirewound. I have an Eico 720 and I'm 99% sure that the drive level pot is wirewound in mine. It's just part of a DC divider that sets the screen voltage on the 6AQ5 driver/multiplier. There's no AC so wirewound should be fine. Lotsa radios in the 50's/60's and QST construction articles show drivers with wirewound pots on the DC screen divider. It has to dissipate a good chunk of heat. The way that Eico built this radio there are all sorts of resistors to drop from the HV to B+ for the oscillator/driver, it gets real toasty due to all those dropping resistors. Last time I looked 50K 5 or 10W pots were available in wirewound, I think Allied or Mouser had the Ohmite units. I don't think you'll find this sort of dissipation available in a ceramic pot. I'd recommend that you go for something more than 4W if you replace it because it does get warm. Tim. |
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