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June 27th 05, 04:41 AM

wrote:
From: Ken Scharf on Jun 25, 6:26 pm

wrote:

I am looking for a nice schematic, and perhaps additional info, on a 12V
(fil. & plate) tube superhet Rx; just something fairly simple for CW/SSB
reception without bells and whistles, and preferably for 75M/40M reception.

Can anyone point me to info on this? Thanks.

Setchell-Carlson managed to do it with loctal-base tubes running
off of a 24/28 VDC aircraft bus back in WW2 times. No dynamotor,
just that cute little box referred to as a "range receiver" or
BC-1206.

Don't remember what the IF (135 KHz) BW was, but, running with
a crystal-controlled converter ahead of it, the 195 to 500 KHz
tuning range could cover 75 or 40 meters no problem. A thought.

I've got one of those in the junk box. I was thinking of converting
it to solid state using cascaded (J310-311 and 2N2222) transistors,
perhaps a differential set of J310's for the mixer and a single J310
for the oscillator. Not sure about the audio and detector stages yet.
There was an article in an old '73 magazine on converting one of those
sets to solid state and adding a crystal controled converter to receive
40 meters. I've misplaced that issue though.

Converting a "Q5-er" from tubes to FETs would be rather easy.
No real need for the 2N2222s. Would have gobs of space left over
inside an already compact box.

This is the idea of a cascade fet-bipolar circuit. The drain of the fet
drives the emitter of the bipolar and the bipolar's base is biased so
that the base sits about half way up the power supply (two resistors).
The fet is self biased with a source resistor for the desired current.
The gain of this circuit is higher than a fet by itself, and the output
impedance will be higher.
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If the 135 KHz IF has an equivalent total Q of 100, the BW would
be about 1.3 KHz, not all that swift for CW and too shart for SSB.

The AnArc-5 Q5'ers had 6 tuned circuits in their If but the '1206
only has 3 or 4. So it's BW might be a tad wider. The 1206 also has
no bfo.

However, the BC-1206 tuning range of 195 to 500 KHz results in
an image at the converter input of 390 to 1000 KHz away from the
desired band. That's worse than the 910 KHz image of an old
455 KHz IF.

The 1206's dial only goes up to 400khz, but it tunes past that. Maybe
it goes to 420 or 450khz, I don't think it goes as high as 500khz.
(so maybe I don't have to expand the range for my needs).

The BC-1206 tuning drive wouldn't be fine enough for today's
narrowband style of operating so that would need a fair amount
of mechanical rework. User's choice there.

The vernier drive isn't that bad. I could put an elcheapo 1.5" vernier
dial to drive the tuning knob (if I modify the drive to remove the 180
degree stop). But I think all it really needs is a better bigger knob.

The linear-in-capacity rotation of the 3-gang variable is good
for an RX Noise Bridge having an expanded parallel-C range...
which is what I used them for. :-)

True, but the rig is just to cute to canabilze.