Maybe something as simple as a cold solder joint on the switch?
Jerry NY2KW
-----Original Message-----
From: r-390-boun...@mailman.qth.net <r-390-boun...@mailman.qth.net> On Behalf
Of Byron Tatum
Sent: Sunday, January 12, 2025 9:24 AM
To: R-390 Mailing List <r-390@mailman.qth.net>
Subject: [R-390] R-390 IF Deck
Hello- I picked up a nice condition clean R-390 IF deck, checked it out and
got selected tubes in it, and tested it in an R-391 receiver I have here.
Allowed it to run about an hour. It is working well as best I can tell but I do
have one issue that bothers me. Based on the carrier meter reading the 8 khz BW
position is about 12 dB down from the 2,4 and 16 khz positions (these 3
positions are all fairly close in reading). I have studied the theory of
this IF deck and how the 8 khz BW is done. I have carefully gone through the IF
alignment procedure as follows - 1. Fed in 455.000 khz from generator
through receiver test point on RF deck
2. Placed BW in 0.1 Khz position and tuned gen for max reading (I
assume this is done to align IF for the particular freq of crystal in crystal
filter Z-501). Leave gen set here. 3. Placed BW in 2 khz position and
adjusted T-506,505, 504, 503, 502 for max reading on VTVM connected to diode
load terminal on rear panel. 4. Placed BW in 8 khz position and adjust
T-501 for max.Have done this several times but get same results. Another
question I have is in regard to the glass metal sealed capacitors throughout
this deck. Friends have told me they have never seen a bad one, some of them
have many years and much gear using them. I did replace the pair of 1.0
ufd at 400 vdc oil caps with high quality film, and dotted silver mica caps
(100, 180 pF) going to ground off of pins 8,9 of V-507 limiter and C-543 (220
pF) going from Z-503 to AGC rectifier V-510. Have not replaced any of these
same type caps in RF circuits.Thanks,Byron W5FH
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