I've played around with a Kenwood TS520... using a softrock
connected in through the filter board. The combination was in a
word AWESOME... if a different radio even thought on frequency, I
probably would have heard it (voice QRM became the limiting factor -
static and hiss less of a barrier). I plan on eventually using the
softrock as an IF and the filters (and so on) for transmission. The
good thing is that the tuned circuits in the old radio are going to
greatly improve the signal, one way or another. In fact, they
should be at least as clean as the best modern unit.
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There are more powerful old tube rigs 'out there' - I can think of a
KW rig right now that would be awesome as an amp (plus great
filtering) for a BitX (or softrock).
Right now I'm trying to get something on the air with 2m SSB/FT8.
Then other projects will follow...
On 11/9/19 5:01 PM, Gordon Gibby wrote:
Finally got a chance to try my idea of using a heathkit ssb rig as
a power amplifier for a QRP rig. I've seen "amplifiers" for
these rigs going for many hundreds of $$$. I happen to be
swimming in ancient heathkits with 2x6146 linear finals and tuned
plate circuits on the driver as well (all good for getting rid of
Allison gave some much needed advice on this crazy idea months
back, and I finally got the chance to try it:
1 watt output from an exciter [I used an icom 718 that was readily
availalbe] -- my only "power measurements" are ancient SWR meters
with built in diode detectors so these measurements may be fairly
coax over to a 49:1 homebrew balun our group made for matching
resonant half-wave antennas: ours is a simple autotuner with 14
turns total of #18 teflon wire around a FT-240-43 (or FT-140-43)
tapped at turn 2 to give us 7:1 turns ratio, 49:1 impedance ratio,
and that checked out roughly with an antenna analyzer and some
I loaded the output with 2500 ohms (temporarily made out of 4 10K
resistors in parallel because that is all i had)
output of that via 6 inches of small coax to a 0.01 1kv ceramic
capacitor connecting to the PLATE circuit of the removed 6CL6
driver, and to a nearby ground.
Output tested only with very brief bursts of CW -- on 80 meters
and 20 meters, got approx 40-50 watts output measured also with an
ancient swr meter/wattmeter into a 50 ohm load, everything on the
Heathkit peaked for output. Plate current rose appropriately.
Tuning circuit all appeared appropriately.
No obvious signs of any instability in this pilot test.
Did not make any measurements with spectrum analyzer. (In due
That heathkit has other problems elsewhere but the finals appeared
in fine shape. Earlier VERY CRUDE measuresments with a siglent
oscilloscope and some math suggested that the drive required at
the INPUT to the 6CL6 stage would be less than 100 milliwatts, and
that the drive required at the output of 6CL6 would be in the
single digit watts range. The above test appears to confirm
those crude measurements. Since it appeared the two 6146's could
be driven adequately with single digit watts I opted to
temporarily just remove the 6CL6 driver and connect to its (DC
powered!!!!!!! High voltage!) plate circucit with a 1kv .01
Quite pleased with this very very initial test.
At some point I'll repeat with a uBitx, but that's all for right