[R-390] Stage Gain Question

[Jacques Fortin]

Hi Barry,
The 1st mixer is bypassed in the 8-32 Mc range.
See the Block diagram on page 141 of the TM 11-5820-357-35.

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 : 28 octobre 2024 22:48
À : R-390 Mailing List <r-390 at mailman.qth.net>
Objet : [R-390] Stage Gain Question

After removing the RF deck (twice - don't ask..) and, other than finding one
of the mini-banana connectors on Z221 had let go of its post (again), I
didn't find anything of interest so I reattached that mini-banana (using a
bit more heat and making sure it was solidly connected), I reassembled the
RF deck.  After a touch-up on the realignment of Z219, Z220, and Z221, and
resetting the RF gain, I can tell the noise level on BCB is down from the
way it was.  Not dramatic, but I think it's an improvement.

I then started back checking the stage gains and am still seeing low gain at
the first mixer for all but the 0.5-1mc band; however, there's a few things
about that process I don't understand.

The table that defines the gain for Test Point E208 shows the acceptable
signal generator voltage range to produce -7v at the DIODE LOAD for 0.5-8mc
which makes sense.  It also shows the 9-18mc range and that part doesn't
make sense to me.  In the circuit description for the First Mixer, it states
that "In the 8- to 32-mc range, the front section of S210 grounds the output
circuit of V203" and that can be seen on the schematic as well.  With the
output grounded, then how is any output of that part of the circuit realized
on those bands?

Thanks,
Barry - N4BUQ
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