[Amps] Filament Choke mod

Thomas R. Williams n2cu at magtrol.com
Tue Jun 15 13:00:44 EDT 2004

The filament voltage on my Drake L7 is 5.25 V, which conventional wisdom says is too high by about 0.3 V. I'd like to avoid placing a series resistor in the primary of the filament transformer since the antenna relay gets powered by another secondary on the same transformer and I'm building in a relay speed-up circuit - I need the extra voltage for that.

The filament choke appears to be wound with 11 AWG formvar wire. I calculated the additional resistance needed to drop the voltage and found that rewinding the choke with 14 AWG wire would do the trick, as far as resistance goes. If I use the same number of turns, should I be concerned about the inductance being a different value due to the wire size? Any other things to consider looking at?

Tom N2CU <><

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