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
