[Milsurplus] BC-611

[ac2eu at yahoo.com]

The IRF510 has less gate capacitance, but is only 100v


Sent from my undisclosed bunker location

On Sunday, August 30, 2026, 3:16 PM, ac2eu--- via Milsurplus <milsurplus at mailman.qth.net> wrote:

To get any power out of the original parts , you would have to maintain the original b+ voltage.That would be both audio out and final. Try a mosfet like rcx081n20 for those jobs. Not an RF transistor, but good enough for 80 meters.I think they use a zener diode in the drain circuit for the low voltage small signal fets.I did a r391 in fets. The only thing that was problematic was the AGC control. The conversion was easier because the b+ is only 24v.


Sent from my undisclosed bunker location

On Sunday, August 30, 2026, 3:06 AM, Hubert Miller via Milsurplus <milsurplus at mailman.qth.net> wrote:

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Yes, i was aware of FETRONS. Don’t think i have any schematics, tho. There were also FETRONS to replace valves
 
in some Telco eqpt, but i never saw any such in the years i worked there. I think HP audio generator or voltmeter or
 
some such. They have to be circuit specific, i think, because they need to drop the B+ from around 100 – 200 volts
 
to 12 to 24.
 
I think i have a book on the ‘Command Sets’ that shows the conversion; also i think CQ or 73 mag had an article.
 
But the transmitter is harder, or should i say, more challenging. I would like to keep the original working voltage
 
so no need to tap the output RF coil or add another audio xfmr to drive the modulation xfmr. Got to think about
 
that some more. Like i said, the fellow who sold the 2 converted BC-611 did not care to share his work. Maybe, i’m
 
guessing, it was too bone-headed and he didn’t want to admit that. Like a straight 1:1 conversion and the same
 
simple JFET all the way thru.
 
-Hue
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