[Boatanchors] Re: Collins R-388 vs 51J4

[Al Klase]

Hi Bill,

Actually, that was my original comment, and I stand by it.  The R-388 
and 51J4 are similar in this respect.  You have to get back at least to 
the 51J2 to see the difference.  I looked around the web, but couldn't 
find the appropriate schematic.  I had one of these sets 20-some years 
ago, and someone at the plant was kind enough to send a schematic, which 
I still have.  The antenna input is a three terminal (A A G) affair 
connected to floating primary windings on the RF coils (actually, the 
middle terminal has 100K to ground to bleed off static)  Good 
engineering practice for 1948 or so.  I'd wager the input impedance is 
400 ohms or so, a good compromise when you don't know what antenna will 
actually be connected.

As someone pointed out, the military wanted good performance on a whip, 
and the design got changed.  There was a article somewhere describing 
the procedure for putting the primaries back in.

For those who believe Collins could do no wrong, pull the rectifier tube 
out of a 388/51Jx.  You'll find there still low level hum in the audio 
output.  The output and power transformers couple magnetically.

Al

Bill Cotter wrote:
> Robert,
>
> Examining the 51J4 schematic on the CCA site, the 51J4 uses the 
> identical Hi-Z input design as the R-388 and 51J3 use.
>
> http://www.collinsradio.org/51J-4-_4th-ed-09-58_-Sec7.pdf
>
> I don't see the difference you are referring to regarding Lo-Z and 
> well-healed civilians.
>
> 73 bill n4lg
>
>
>
>

-- 
Al Klase - N3FRQ
Flemington, NJ
http://www.skywaves.ar88.net/