[Boatanchors] 51J's vs R-338's?

[Bob Kulow]

<snip>
> 
> Anyone ever put a product detector in a R-388? How does that 
> set up compare to a 75A-3 with product detector or 75A4?

Yes, I did some years ago.  As I remember, one half of a 12AU7 
is used as a diode for the second detector.  I added a 1N457 
(I think) for AM detection and converted the 'AU7 to a product 
detector, using the same circuit that National used in the NC-190.

I didn't make any changes to the AGC.  It seemed to work well 
enough as is.

It worked nicely except for the IF signal being a little too 
strong into the new product detector, requiring the RF gain 
to be reduced a slight bit.

The RF conversion scheme used inverts the sidebands on some 
bands and not on others so you can't mark the BFO tuning for 
USB and LSB.

Also, the 51J-4 is different from the R-388 or 51J-3.  The 
'J-4 has 3 mechanical filters added to it which the 'J-3 or 
'388 don't have.

73
Bob WA2UEH

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