[Milsurplus] More BC-474 Fun

[B. Smith]

I get in trouble every time I try to list names and calls. I forget to 
include Mike
KC4TOS his contribution which includes a detailed machine sketch of the 
Speed-X "Hold Down Screw." Link is on my page or you can go direct to 
Mike's "Garaj Mahal."
https://aafradio.org/garajmahal/hardinge.htm
K4CHE

On 7/11/2025 11:21 AM, B. Smith via Milsurplus wrote:
> Finding the various components of the SCR-288/BC-474 can be a 
> challenge. One item the telegraph key is all most impossible to 
> locate.  I know it is just a chrome Speed-X key but they don't make em 
> anymore and this  version of the Speed-X key had a Hold Down knob 
> installed and a wooden base.  I've included info from Al's page and 
> others and tried to combine all the info on one page. See link. 
> Contributors include Dave AB5S, Al N3FRQ, and excellent sketch by Paul 
> N6FEG. My personal key belonged to Emidio WA2FSX now SK.
>  K4CHE
>
>
>
> http://k4che.com/BC474key/BC474key.htm
>
> On 7/6/2025 8:10 PM, Al Klase wrote:
>> 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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>
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