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

[Barry Scott]

Jacques,

It's not a short 6C4 - just a standard height version.  I'm not sure of the
manufacturer but I do have some spares I can try.  The output of the 1st
crystal oscillator appears strong on an oscilloscope and is about the same
magnitude as the 2nd crystal oscillator's output.

You have made me realize that I did not align the two variable IF
circuits!  I completely neglected to do that as I was focusing on the RF
sections. That very well might be where the problem is.

Thanks!
Barry - N4BUQ


On Sun, Sep 22, 2024 at 9:25 PM Jacques Fortin <jacques.f at videotron.ca>
wrote:

> 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
>
>