[Milsurplus] BC-474 RF ammeter ?

[Al Klase]

Hello Hue,

My MI-8751/SCR-288 came to me missing the RF ammeter.  The original 
meters are Bakelite black, BTW.  I replaced it with a junk  box meter 
that is virtually identical to the 100 mA plate meter.  If memory 
serves, I removed the shunt, and the basic movement was something like 1 
or 5 mA.

Anyway, wind 10-15 turns of wire on a ferrite toroid, mix 2 or mix 6 
(yellow or red) would be good.  Connect this winding to the meter via a 
germanium diode and a series resistor.  Diode cathode goes to + on the 
meter.  The connection to the original meter makes one pass through the 
toroid.  Adjust the series resistor for the desired response.  Because 
your going from a whole amp in the antenna circuit to a couple of mils 
in the meter, there's a lot of room for slop.  This 
RF-current-transformer stunt has proved helpful in a number of cases. 

The RCA "Swedish Set" is one of my favorite radios, and has served well 
into all sorts of loads.  Just tune for maximum antenna current.  50-ohm 
loads have never seemed to be a problem for me.

best regards,
Al

Hue Miller wrote:
> What would you suggest using to replace the missing RF ammeter
> on a BC-474 ? Using something like a sensitive movement to 
> measure the voltage across a small resistance in series with the
> antenna lead?  Or just measure the antenna voltage?  Is there an
> antenna tap that matches 50R better, or should the antenna coil
> be retapped ?  Are these Simpson "art deco" ( due to the streamline
> lines on the bottom of the meter case ) hard to find ?
> I have one that's been painted an almost dark blue or charcoal
> or very dark blue-green color, almost looking like some piece
> of Japanese or Wehrmacht  radio. Inside the case, you can see
> the original OD color. When I first saw this set, I thought because
> of the color, it was one of the RCA MI-nnnnn labeled early sets,
> similar color. Is this more likely a hammy repainting? The only
> thing that makes me hesitate to jump to this conclusion is that
> the leg fastener rings and all the external hardware are very 
> well painted. Tnx-  Hue Miller  
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-- 
Al Klase - N3FRQ
Jersey City, NJ
http://www.skywaves.ar88.net/