I had in the mid 1970s A.D. an ARR-15 i bought from a vet. It was MARS - acquired and still in some kind of large cardboard barrel. I bought from Fair a 24 DC supply and ran it that way. Yes, there is a definite "noise floor" running on dyno, altho i did hear some interesting SWL type things, such as a game show over BBC, just above 5Hz, Kuching Malaysia. My barber, who is from Malaysia, was surprised at this story.

I have 2 of ARR-15 now, one with dyno. The odd thing abt the one with dyno is, the pushee antenna connector has been changed to BNC. I don't get that. If it's a ham mod, why run it on 24 DC still ? When i did run it on 24 DC, i had an excuse: i didn't know better.

There used to be on the net some article abt tightening up the IFs by decreasing the low pF coupling caps. Article is gone now. I wonder if anyone here has done that. I think the tuning rate is too fast for CW and certainly SSB, so i'm thinking the +- 50 kHz 'calibrate' feature can use improved selectivity. In other words, to be clear, can one improve the selectivity and use the +- IF feature for fine tuning ? In those olden days, for SWL BC, AM mode only, the main tuning knob was good enough. 

Another thing i want to figure out is that audio filter. The manual doesn't really explain its working or innards. 

Lastly, let me mention that i never noticed any audio distortion from the always - on noise limiter. That circuit actually does have its own unique name, after the designer, but i cannot remember it at this moment. 

-Hue Miller