[Milsurplus] WWII Navy RU- Receiver Coils.

[Hubert Miller]

Well, your RAL has something called regeneration, which made it actually selective enough to use on HF AM reception. 
Also the RAL has a selective audio filter.
Also it has reasonable frequency travel for tune control motion. 

Think about using the RU on say, around 10 MHz - altho it does go up thru 13+ something. 3 tuned circuits at 10 MHz, what
kind of selectivity does that buy you?  
As a direct conversion receiver for CW, the story is a little different; more usable, altho there's still no audio selectivity, and 
the tuning rate is still fast, 100 dial divisions per tuning range. Also the detector  ( mixer for direct conversion ) is not 
optimized if you want to use it as a direct conversion receiver CW only. Then the bias on the detector would need to be
reduced. 
I understand the RU was pretty easy to use in aircraft, I mean for voice. You basically couldn't knock or vibrate it off frequency
nor would the other guys transmitter drift out of the passband. I saw some photos of RUGF or SCR-183 equipment installed 
in Japanese aircraft being performance tested here and I guessed that was because the receiver was so uncritical to set up.
( Monogram "Japanese Cockpit Interiors Vol 1 and 2 - not worth buying though. )
But I don't think anyone has solved how to use the RU on the air for AM nets. I thought about it a lot and came to no conclusion. 
suppose one could use a 2 terminal Q multiplier circuit connected to the first tuned circuit but then you need an external control knob too. 

I asked Pete Peterson about the RU once, kind of expecting him to have a lowly opinion of it, and he said, he thought it was
a pretty good little receiver. But he was only using them in CW use on PBY aircraft, post-WW2. "Should have" asked Pete more
questions, put it off and put it off, and then he was SK. 

I think I recall the ER article saying the RU was inferior in many, most? respects to the later "Command Sets". No surprise there.
I don't dislike them. I kinda like the black machine instrument look. I still have several and I'm tempted time to time to get a 
complete RUGF together. But I always come back to thinking, I'll farm this project out to someone else.
-Hue