Here's hoping you're not a liar this time, Eddy! If it was the resistors, I would say that it was an unusual failure mode. The problem with chasing intermittents is exactly what you (and I) ran into: the problem would go away for a while, only to resurface later. I was lucky in that the capacitor change solved the problem.
I still don't know what else was happening when I had the PTO from the T-4XB in that R-4A. I subsequently set up a test bed and ran it on a regulated supply into a 200 MHz Fluke counter for over a week and it never budged. The receiver has since gone on to grace another ham's shack and I haven't heard of anything funny going on there (I had to sell mine to buy the B-Line..) It was working great for weeks after the fix, though. Good luck, Eddy, and we're all pullin' for ya! 73, Steve, W1ES/4 -----Original Message----- >From: Eddy Swynar <[email protected]> >Sent: Nov 23, 2011 1:01 PM >To: [email protected] >Subject: [Drakelist] The Drake PTO Yet Again... > >Hi Guys, > >Not intending to flog a dead horse here, or anything, but I do feel compelled >to let everyone in on my latest---and hopefully FINAL!---attempt at taming the >squirrely PTO in my T-4X transmitter... > >Last week I extricated the PTO board from its enclosure & mounts, and I >outright replaced each & every fixed resistor associated with the oscillator >stage itself. I used "fresh" 1/4-watt "flame proof" resistors that I purchased >out of a place in Toronto. The theory behind all this was simple enough, i.e. >if 40+ year old capacitors can change with age, then why not 40+ year old >carbon resistors, too---especially when they're under load? Surely even a >MINUTE change in an aged resistor's value could have a noticeable effect on >the stability of a solid-state oscillator---especially if said resistor is in >a lead connecting the transistor to its source of voltage, right...? > >Anyway, some 10, or so resistors later (I got bleary-eyed from focusing on the >small components!), I re-assembled everything, and have been testing the >transmitter for a week now. The previous oh-so-gradual creep in the PTO's >frequency---and the resultant sudden drop back to the original frequency---has >disappeared. Ditto the sudden & "unannounced" frequency jumps of 1-2 KHz. >There is no more warble, either... > >I guess the point of posting this is two-fold: firstly, if you're plagued with >an unpredictable PTO as i was, the final "fix" can be two-fold, three-fold, or >even more! Secondly, whenever I've posted my past "successes" in this regard >on the Reflector, the T-4X has ultimately & consistently proven me to be a >liar! Hi Hi. Let's see if I might get fooled again with this one... > >~73~ de Eddy VE3CUI - VE3XZ > > >_______________________________________________ >Drakelist mailing list >[email protected] >http://mailman.zerobeat.net/mailman/listinfo/drakelist _______________________________________________ Drakelist mailing list [email protected] http://mailman.zerobeat.net/mailman/listinfo/drakelist
