[R-390] Low gain 0.5 MC through 7 MC

[Jacques Fortin]

Barry, the troubles of your R-390/URR reminds me a lot of similar things
I've gone thru with mine....
Yes, it can be the first mixer tube: I just hope that is not a "dwarf"
Raytheon 6C4W used there.
Or it can be something around (any component in the plate circuit) Z221
again ???
The problem can also be the first crystal oscillator (V401) which do not
have enough output...
Check every component around and swap the tube for a known good one if you
have spares.

73, Jacques, VE2JFE in Montreal

-----Message d'origine-----
De : r-390-bounces at mailman.qth.net <r-390-bounces at mailman.qth.net> De la
part de Barry Scott
Envoyé : 22 septembre 2024 20:37
À : R-390 Mailing List <r-390 at mailman.qth.net>
Objet : [R-390] Low gain 0.5 MC through 7 MC

Sensitivity on the lower 7 bands is significantly lower than on 8 MC and up.
I can see this very readily with the signal generator as input and, with the
output level remaining the same, switching from any of the first 7 bands to
8 MC or higher shows a significant (approximately double) rise in the
radio's dB meter.  It's also noticeable just listening to stations.

The common factor seems to be V203 (1st mixer) and I suspect that tube might
have low gain (possibly gassy?).  Is that a reasonable thing to start with?
I don't see how something affecting the AGC would affect all the paths to
V203's grid and so I was thinking the tube itself might be the problem.

Thanks,
Barry - N4BUQ