[R-390] 2 diode agc ssb mod c/l meter linearity

[Jordan Arndt]

----- Original Message ----- 
From: "David Wise" <David_Wise at Phoenix.com>
To: "Larry H" <larry41gm at gmail.com>; "R-390 Forum" <r-390 at mailman.qth.net>
Sent: Friday, August 27, 2021 9:06 AM
Subject: Re: [R-390] 2 diode agc ssb mod c/l meter linearity


> * An alternative to Jan Skirrow's op-amp mod, this minor IF Deck design 
> change lets you drop in virtually any meter movement without modern 
> technology.

Just an FYI...

I use a Carrier Level meter ckt similar to the Skirrow and KH6GRT op-amp 
mods, but I use a 741 Op-amp with different component values...The small PCB 
also mounts on the rear of the meter, but it could be made much smaller and 
mounted elsewhere if the builder chooses to do so.

The circuit is very similar to the KH6GRT ckt found here:

https://www.qsl.net/kh6grt/page4/R390meters/CarrierMeterAmp.pdf

The values I use are:

R1 18 ohms 1/2W (what I had on hand)
R2,R3  2700 ohms 1/4W
R4 100K ohms 1/4
R5 5Kohm multiturn variable
R6 not needed
C1,C2 25uF 16V
C3 not needed

It is very linear from 20 to 100dB on the A&M Inst. 0-100dB 1ma FS 
calibrated meter I'm using in my 1959 Stewart Warner 390A.

73...Jordan VE6ZT