[Milsurplus] More BC-474 Fun

[Al Klase]

Folks,

I'm a long-time fan of the SCR-288/MI-8751/BC-474.  The design is based 
on RCA's AVR-21 aviation radio from the 1930s.  It' was pretty 
sophisticated for the time.  See my webpage: 
http://www.skywaves.ar88.net/mil/SCR-288/SCR-288.html

AL

On 7/6/2025 2:53 PM, Ray Fantini via Milsurplus wrote:
> Before I started this project always thought the BC-474 (SCR-288) was 
> a bit of a Dog. Not built to MIL standards, odd shape and size 
> compared to the radios that came after and underpowered for what it 
> is. Looking at the design of the receiver with only one stage of IF 
> and the transmitter that appears to be right out of the 1947 ARRL 
> handbook I had low expectations. Once I started working on it with its 
> multiple old style leaky capacitors and mysterious “Cap Pack” stuffed 
> full of the same I did not expect much.
> Built up a BA-48 battery pack and got the receiver working first, OK 
> it’s not the most sensitive receiver but in CW works well down to a 
> couple micro volts and has good AVC action in AM. Somehow the set 
> reminds me of the old Navy TBX set but unlike the TBX this receiver 
> has a working AVC system, and the audio quality is not that bad 
> considering the entire receiver only draws around 10 MA @ 90 volts 
> being just about the same as the TBX. Into a fifty Ohm load with only 
> a couple hundred volts for the transmitter developed a good couple 
> watts in AM or CW, spurious down at least forty Db on the second and 
> did not see any other artifacts.  Ok, so the transmitter dose have the 
> issue with C13 being in the wrong place, the decaying CW chirp when 
> changing between transmit and receive in CW sucks and will have to 
> change that but all in all have to say despite a lot of the ideas I 
> had going into this I now see that I was wrong. Have to say that in 
> comparison to things like the BC-654 or later GRC-9 this strange 
> little radio more then holds its own and, makes a fun little field QRP 
> or Show set up.
>
> Ray F/KA3EKH
>
>
>
>
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-- 
ARK Sig Block Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/
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