[R-390] Strange variation of sensitivity AGC resistance toward the chassis

[Roy Morgan]

On May 4, 2015, at 6:12 AM, Pierfrancesco Mengacci <pf.mengacci at outlook.it> wrote:

> Just for scruple, does someone know which is the “normal”  value of the AGC
> circuit resistance toward ground , measured at the rear contacts of TB 102
> (n° 3 or 4), when the receiver is set on AGC function and disconnected from
> power supply ? (AGC delay setting: medium)

No, but I can get to a receiver today and measure it.  I’m pretty sure this has been reported on the list, and is likely to be found in the Pearls of Wisdom.

http://www.r-390a.net/Pearls/index.htm

The IF deck section is:

http://www.r-390a.net/Pearls/IF_deck.pdf

Note that this is some 500 pages long.

> In my case, I read 380 Kohm (when the negative terminal of the ohmmeter is
> connected to the chassis, it has a minor influence...). This reading takes
> even 5 minutes to stabilize.

I think you have bad capacitor(s) in the AGC line, or leaky wires.  All your reported symptoms point to this.

Roy


Roy Morgan
k1lky68 at gmail.com
K1LKY Since 1958