[Collins] 75A4 sensitivity

[Dr. Gerald N. Johnson, electrical engineer]

I don't agree that alignment is a good diagnostic. The only radios that
really need alignment are those that have been "aligned" by persons with
a screwdriver and poor knowledge of alignment procedures. I believe that
a radio should be made to work, find the bad capacitors, the fried
resistors (and the old black beauties can often overheat screen dropping
resistors) and the badly drifted resistors, and only then the alignment
be tweaked if the performance is bad, as Bill found by poor AGC
performance. When there is a circuit problem, such as a bad bypass
capacitor, proper alignment may not be possible and may lead to
misalignment, e.g. increasing signal at the detector by detuning the AGC
IF stage.

There has been a myriad of mods for the A4 in the magazines.
Occasionally one was good, many were bad. RF tube substitution with
something having 5 times the gain would give the symptoms Bill
experienced. Namely oscillation.

73, Jerry, K0CQ, Technical Advisor to the CRA.
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.