Okay. So simply go by the markings of what's in there as that is what the factory installed and should be followed. Understood.
Thanks, Barry - N4BUQ On Sun, Jan 12, 2025 at 2:38 PM Jacques Fortin <jacque...@videotron.ca> wrote: > > Hi Barry, > Read TM11-5820-357-25, page 17, chapter 17c. > Or in the TM11-856, page 56, Chapter 63 (more complete explanation there). > If the measured resistors value there (including R519) are not matching > their color bands indicated value, that could affect the gain of the 3rd and > the 4th IF stages when a given BW is selected. > Those resistors values were selected during manufacture to equalize the gain > of the IF strip, probably by taking the 16kHz BW position as the reference: > R518 is the only value being specified at 220 ohms.... > The latest schematics shows R519 as being a 900 ohms, but the original part > can be of any standard value between 560 and 1100 ohms. > However, the only place that this information is available is in the > TM11-856, Figure 38 (TM856-38, note 2). > Or in the 1953 Collins manual that pre-dates the TM11-856. > > 73, Jacques, VE2JFE in Montreal > > -----Message d'origine----- > De : r-390-boun...@mailman.qth.net <r-390-boun...@mailman.qth.net> De la part > de Barry Scott > Envoyé : 12 janvier 2025 14:42 > À : Jacques Fortin <jacque...@videotron.ca> > Cc : R-390 Mailing List <r-390@mailman.qth.net> > Objet : Re: [R-390] R-390 IF Deck > > To clarify that a bit, R519 was selected from 560 to 1100 ohms. The others > were selected from different ranges. Sorry if that was misleading. > > Thanks, > Barry - N4BUQ > > On Sun, Jan 12, 2025 at 1:40 PM Barry Scott <72volkswa...@gmail.com> wrote: > > > > The schematic for the 4th IF Amplifier shows R519 (and others) to be > > selected from a range of 560 to 1100 ohms. Anyone know the criteria > > for how that was selected? > > > > Thanks, > > Barry - N4BUQ > > > > On Sun, Jan 12, 2025 at 9:55 AM Jacques Fortin <jacque...@videotron.ca> > > wrote: > > > > > > Hi Byron, > > > > > > As there is only the 8kHz BW that develops less gain than the other > > > positions, my prime suspect for the problem you experience will be R519. > > > The cathode bias for the 3rd and 4th IF stages depend on different > > > resistor values switched by S504 to "balance" the IF gain VS the desired > > > BW. > > > R519 is responsible to set the global gain of the IF for the 8kHz > > > position. > > > If ever the actual R519 value is way higher than it is supposed to be, > > > the gain in the 8kHz position will be lower than it should. > > > > > > The second resistor values to check are all the 2.7 ohms resistors (R507, > > > R514, R524, R534) because they are used only in the 8kHz position again. > > > Normally, these resistors are an early form of carbon-film construction > > > and should not have failed, but who knows ? > > > Also check the corresponding IF transformer windings for continuity: a > > > failure in one of those cannot be excluded. > > > > > > For the metal-glass sealed capacitors (Sprague Vitamin Q): they are the > > > longest lived paper-in-oil types that were ever made. > > > If there is no sign of oil leakage around the wires exiting from both > > > sides, they are surely still good. > > > You can perform an electrical leakage test on some to be sure. > > > But if there is signs of oil that leaked from those, that means that the > > > oxygen also gets in and turned the internal oil in something else (the > > > PIO disease) that result in value change, leakage and ESR rise. > > > > > > 73, Jacques, VE2JFE in Montreal > > > > > > 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 > > > > > > ______________________________________________________________ > > > R-390 mailing list > > > Home: http://mailman.qth.net/mailman/listinfo/r-390 > > > Help: http://mailman.qth.net/mmfaq.htm > > > Post: mailto:R-390@mailman.qth.net > > > > > > This list hosted by: http://www.qsl.net Please help support this > > > email list: http://www.qsl.net/donate.html > ______________________________________________________________ > R-390 mailing list > Home: http://mailman.qth.net/mailman/listinfo/r-390 > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:R-390@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ R-390 mailing list Home: http://mailman.qth.net/mailman/listinfo/r-390 Help: http://mailman.qth.net/mmfaq.htm Post: mailto:R-390@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
