[ARC5] Modifications...more...

[Kenneth G. Gordon]

As far as I have been able to determine, there are only three basic areas in 
which there have been any significant advances in receiver design since 
WWII: those are 1) mixers, 2) detectors, and 3) AGC circuits, almost all of 
which are the result of the development of SSB.

In the case of the ARC-5 receiver, all of those could be improved to reduce 
receiver-generated noise, to improve the efficiency of the detector, and to 
improve SSB and CW detection.

However, those receivers work JUST FINE as is for their intended purpose.

My major complaint with the ARC-5 receiver is that crappy, crappy, noisy, 
noisy 12K8 pentagrid converter whose ENR is something over 280,000 
ohms.

But that tube and circuit was the latest development of that sort of mixer at 
the time.

As far as the mixer is concerned, one can easily build a dual-dual triode 
(using submini 7963s)  "Pullen" mixer on a used octal tube base, and plug it 
in place of the 12K8.

This vastly reduces internally generated noise, and improves stability (which 
isn't all that bad to start with). 

Ken W7EKB