[ARC5] Frequency shift with percussion

[Scott Robinson]

Folks,

I have part of an RF noise meter, essentially the front end and IF strip 
of a nice multi-band radio, built in large part with subminiature tubes. 
It needs a detector, power supply, and audio amp.

I have it restored and working, but as the upper bands use a 1600 KHz 
IF, it could use better selectivity. I've thought about a non-crystal 
controlled down converter to 455 so I can buy a 7 KHz BW (no SSB use 
contemplated) crystal filter and sharpen up both IF frequencies with the 
same filter. I expect I can make a stable enough 2055 KHz conversion 
oscillator without fussing with crystals, so long as I keep the 
oscillator coil away from local heat sources or temperature compensate it.

The detector will of course have a separate AVC rectifier so it can get 
down to 90+% negative modulation, and will have fast attack/slow decay 
timing. The audio will be to my specs, probably using a 6BX7 PP dual 
triode, good for about 4W,  1-3% distortion and a low output impedance 
for better speaker resonance damping before feedback. I modified my 
Hammarlund SP600 (audio only) with this circuit to good effect, no new 
holes anyplace visible either.

The basic piece will remain largely as it was, except for replacement of 
unobtanium interface connectors.

Keeps the old man off the streets and outa the bars, it does.

Peace,

Scott

On 3/2/15 8:22 AM, Kenneth G. Gordon wrote:
> Speaking of the subject:
>
> I don't know if many remember my battle with a BC-454 which someone,
> back in the day, had begun to modify to cover the 10 meter band, but had
> never finished. However, during my work with this wreck, one of the things I
> had to overcome was severe microphonics, and severe instability.
>
> What I eventually found was that the slugs in the coil-box were all loose and
> were literally rattling around in there.
>
> Filling each coil form with melted bees-wax cured part of the problem.
>
> I suppose the fact that the receiver was now operating on a frequency which
> was close to 10X the frequency it was originally designed for had a lot to do
> with the problems I experienced.
>
> The eventual result was a receiver which covered the 10 meter band from 28
> to 30 MHz, with good sensitivity and decent stability. Selectivity was about
> what one would expect: acceptable for AM, at least.
>
> But believe me, I would never take a decent receiver and do such damage to
> it.
>
> Ken W7EKB
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