[AMRadio] Power Resistor

Geoff w5omr at w5omr.shacknet.nu
Sun Mar 20 20:33:39 EST 2005

Jim candela wrote:

>   I recall someone in your situation using a lower wattage pot, and a HV
>NPN Horizontal output transistor as an emitter follower. A resistor from
>emitter to ground is required, maybe 47K 2 watts. You might think about that
>option. This transistor will need to be heat sinked, and the case isolated
>from ground with a mica insulator, and a little "owl sh_t" grease. If the
>transistor beta is 100 at say 20ma emitter current, then the base current is
>.02/100 or 200 ua. Your pot will stay cool as the transistor does the work.
>In case the output gets shorted, maybe add a 470 ohm series resistor that
>should fry in the case of a short. I'd put that on the collector side going
>to the low B+ since it might quench out a parasitic before it gets started.

or a diode from the collector back to the base, to prevent meltdown.

Jim, that utramodulated Viking I... is that the "engine is in" transmitter?

73 = Best Regards,

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