I have had the 100pf mica go bad in the 17mhz drive circuit. Interestingly it did not check bad, but greatly limited the amplitude of the mixer drive. … Tom, N3LLL
On Sat, Mar 30, 2024 at 1:24 PM Jordan Arndt <[email protected]> wrote: > After a long break from working on 390As, I'm back into a 390A I bought at > least 25 years ago. > > It's the most mongrel 390A I've ever seen, with a modules and assemblies > from S-W, Teledyne, Capehart in an early single fuse chassis of unknown > mfgr. The front panel is a re-paint and re-letter and the ID tag is a > generic after-market type. > > The RF deck front plate and gear assembly is Teledyne with the deck > chassis > being a S-W and with a Capehart xtal oscillator module refurbed at > Tobyhanna(sp?). > > I've gotten a good deal of the required rejuvenation work done, but I > found > an issue where the 1st xtal osc. voltage is rather low when measured as > rectified at E-209. > I cannot get more than 2v DC measured at E-209, while T207 peaks smoothly. > > What I've done so far regarding this problem: > > Replaced the 17Mc xtal, and then the entire oven ass'y including xtals > from > a working radio to no avail. > > I then swapped out the 6AK5 osc tube with several good 6AK5/5654 tubes, > then > did the same with the 6C4 1st mixer tube. Again, all to no effect. > > Since it has been 25+ years since I originally worked on this radio, I > suspected component problems in the RF deck, so I pulled the deck. > > I pulled C275 and C268 as the originals had been replaced with disk > ceramics > (what I had on-hand at the time) but both test just fine at 99 and 105pF > respectively. I'll replace them with S.M. caps. > > I then checked every resistor in the RF deck and aside from R203, which > had > drifted up to 90K from 82K, they all are within spec and show no signs of > overheating. > > Aside from checking feedback caps C324 and C325 to see if one or both have > issues, is there anything else I should look at...? > > Any suggestions or advice would be much appreciated...! > > 73...Jordan VE6ZT > > ______________________________________________________________ > R-390 mailing list > Home: http://mailman.qth.net/mailman/listinfo/r-390 > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
