As an old timer like yourself, in the fifties & sixties I used different receivers, amongst them the Racal RA17 and the Collins 75A4, at the time judged the best.
- With AM reception one kept AGC ON and audio level was adjusted with the volume control.
- With SSB reception one kept AGC OFF, audio level at a fairly high position and volume control was obtained by manually adjusting RF gain. With this procedure perceived noise was minimised, especially in the modulation throughs of the received signal, where received power, with low or no modulation, was at a minimum. This procedure minimized or avoided AGC amplification of internally generated or antenna noise.
With these receivers you only had one AGC circuit, controlling both IF and RF gain.
Comparing the two receivers, the Collins 75A4, a conventional double conversion superhet, is the less sensitive, but, with the formidable front end selectivity afforded by permeability tuning, it almost never overloads with strong signals. The Racal RA17, with its wideband front end and upconversion to a high IF, is more sensitive, but can often overload with strong signals, even far away from the receive frequency.
The RSP class of receivers, because of their structure, are impervious to front end overload and have two AGC circuits, one controlling the gain of the IF section and the other controlling the gain of the RF section: if the RF gain is low, then the self generated noise of the IF section (with the worse noise figure) will prevail. Increasing the gain of the RF section (better noise figure) its internal noise will prevail, minimising receiver's self generated noise. In any case present times antenna noise is at such a level as to render almost irrelevant the issue of internally generated noise. It depends on the operator's experience and skill to adjust the controls in such a way as to avoid antenna noise amplification, like I just found out to my surprise:
https://www.sdrplay.com/community/viewt ... f=5&t=3635
By using these procedures, with the RSP receivers you indeed easily copy signals at the same level as the antenna noise, a feat I was never able to accomplish with "conventional" receivers of time past.