. This brings up another
> question for you experts. I am planning to use vacuum relays, HC1 / RJ1
> types, to accomplish this switching.
A neat scheme I "borrowed" years ago from Creative Electronics (now
Amplifier Systems) Is a bit cheaper and more reliable than you suggest
above.
You need two chokes; one <40 uh or so, so that the first resonance
is parked well above 30 mhz. If you are to include 160 meters, the
second choke needs to be 180-225 uh, with the first resonance parked
well above 40 meters. The bottom of the larger choke is where the B+
is attached, along with c. .01 ufd @ 8-10 kv bypass cap to ground. The
top of the larger choke is tied to the bottom of the smaller choke. Another
.01 ufd or so, 8-10 kv bypass cap is connected to this joint, but it is grounded
through an inexpensive relay of your choice. When the band switch is
moved above 40 meters, the relay energizes, and the RF "sees" only
the smaller choke's inductance and resonance's. D.C. is blocked from
the relay contacts, and only RF current that got through the choke is
flowing through its contacts When operating on 160-80-40 meters, the
relay contact is open, the bypass cap is floating, and the RF "sees"
200-240 uh; quite adequate for 160 meters with the bypass values as
I suggest.
This is how the CE-2500A, 1.8-30 mhz, 3CX3000A7 amp works, and there
are many still banging away out there.
(((73)))
Phil, K5PC
|