[Milsurplus] Receiver Filter Adaptor- From Pillar, Back to Post

[David Stinson]

I just keep tweeking, guys.  Still sticking with the triodes for 
now.

http://home.netcom.com/~arc5/TCS/TCSFilterAdaptor1.jpg
I did try some suggestions, like raising the plate voltage on V1, 
but that did not address the overload.   The whole thing just had 
too much gain.  To get rid of the feedback problem, I used 
aluminum tape to shield the tubes and that worked well.  Want to 
see what "Texas Aggie Prototyping" looks like?
http://home.netcom.com/~arc5/TCS/FilAdapt1.jpg
Tube V1 is on the right, grounded filter case is on the left. 
Fold the metal tape right and it connects to the case to provide 
ground to the shielding.  Used the tape on the other tube and 
folded a wire in it to connect to ground.
The three twisted wires are the filter input and a ground wire, 
run as far as possible away from V2.
http://home.netcom.com/~arc5/TCS/FilAdapt2.jpg
Installed:
http://home.netcom.com/~arc5/TCS/FilAdapt3.jpg

I finally decided that the problem wasn't the low B+ on V1, but 
the excess gain at V2.   I changed the zener from a 100 Volt drop 
to a 200 Volt drop, bringing the B+ to V2 down to about 20 Volts. 
The adaptor works better now than it has since I started.  Not 
perfect, but better and no more overload problems.   I think it 
will be even better with a little bit more B on V2, maybe 40V or 
so.  Will pick-up an assortment of the 1N53xx zeners and tweek it 
for best performance.  The capacitor across the zener doesn't 
seem to make any difference to the noise floor, so I removed it 
again.  Use the BFO knob centered at 455KC and turn down the RF 
gain (as one does in many radios without product detectors) for 
LSB.  Move the BFO -1 for CW (for this 2.1 KC LSB filter. 
Another filter will work differently).  The filter splits AM 
signal sidebands.  Tuning a little higher from zero-beat sounds 
best to me.  One trades-off AM fidelity for CW selectivity.

Things keep looking up.  Still a happy boy.

GL OM DE Dave AB5S