[R-390] BFO Drift?

[ANTHONY CASORSO]

Thanks Tim. That is an excellent response. I am in fact operating on a low band. I can easily check to see if the symptoms track a specific crystal or if they go away above 8 Mhz. I can also check for AGC pulling by going to MGC.
 
Having access to this kind of information is like having and extra brain at your fingertips. I could have poked at this for weeks without making any headway. I will let you know what I find.
 
Tony> Date: Thu, 11 Dec 2008 12:57:59 -0500> From: tshoppa at wmata.com> To: r-390 at mailman.qth.net; canthony15 at msn.com> Subject: Re: [R-390] BFO Drift?> > As to drifts, I know of at least 4 kinds:> > 1. BFO that you're postulating> 2. PTO that you seem aware of as a possibility> > But the kind that I hear most often on 390A's:> > 3. The band-switched crystal oscillator. There are a lot of crystals and having flaky contacts on the crystal or bandswitch can cause drift symptoms like you're seeing.> > 4. AGC-related pulling of the 17MHz oscillator.> > #4 will appear on only the low bands (below 8MHz) and #3 often on one particular cyrstal (which is likely used on multiple 1-MHz wide bands).> > Some of the BFO tuning mechanical couplings can stick in funny ways and then "let go" resulting in shifts.> > >>> ANTHONY CASORSO <canthony15 at msn.com> 12/11/2008 11:59:26 AM >>>> > I have been listening to lots of CW lately and it seems that there is quite a bit of drifting going on in my 67 EAC R-390a. Even after its been on for more than an hour I can hear the signal slide up in pitch over a several minute period. I am pretty sure (but not absolutely sure) that it is the BFO. In my set I have replaced the 3TF7 with a 12BY7. I was listening to beacons using a waterfall display (Argo) and I could see the carriers slowly angle off over a long period and then, within a minute, come back down. The excursions are over 100Hz. The oven switch is off. Has anybody seen this sort of thing before? I have a counter, so I suppose I should put it on the PTO and confirm that it is OK. Just haven't gotten to the point of opening it up.> > Thanks,> > Tony> 
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