Don, Thank you for the very detailed response/analysis - that was helpful. I definitely will heed your advice and replace one component at a time.
73, -Matt W6ZBA On Thu, May 5, 2011 at 11:37 AM, Don Wilhelm <[email protected]> wrote: > Matt, > > That takes only one of the varactors out of the circuit. You could remove > both C2 and C7 and that would remove both varactors from the circuit. But > that still does not eliminate the supply voltage because Q8 will still > change in response to a change in the 6 volt regulator output. > > Other possibilities are that D17 is changing characteristics, or Q9 is > changing a bit which can pull the oscillator. Thermal drift in R7 could > cause changes in the base circuit of Q7. Q8 itself could be another > probable cause. In cases like this it is a matter of replacing one thing at > a time and monitoring the results. Work methodically - wholesale replacement > of parts may or may not correct it. > > If you play air from a hair dryer on the VFO area and note if the rate of > the frequency change increases substantially, then you may be able to > conclude it is temperature related (the core of L1 is then the most likely > suspect). Beware of drawing false conclusions if attempting to raise the > temperature - that WILL change the frequency somewhat even in the best of > times, so the real question becomes a guess as to whether the rate of change > is greater than anticipated or not. If you can find another K1 to compare > your results while applying the same exposure to the normal K1, then you can > draw better conclusions. > > 73, > Don W3FPR > > > On 5/5/2011 11:52 AM, Matt Scholz wrote: > >> Thanks Don. >> >> So here's another question. My first step was to remove C2, which >> effectively removes the varactor (D3) from the equation. I was still >> observing an excessive amount of drift. Doesn't this rule out the voltage >> regulators as the cause of this problem? >> >> 73, >> -Matt W6ZBA >> >> On 5/5/11 7:19 AM, "Don Wilhelm"<[email protected]> wrote: >> >> Matt, >>> >>> I would first suspect the stability of the voltage regulators. That VFO >>> is tuned with a varactor, if the voltage changes, the frequency will >>> change. If that does not settle it down, I would wind L1 on a new core >>> on the suspicion that the present one is more temperature sensitive than >>> usual. >>> >>> 73, >>> Don W3FPR >>> >>> On 5/5/2011 1:40 AM, Matt Scholz wrote: >>> >>>> Hi - >>>> >>>> I am trying to reduce my K1's VFO drift to an acceptable level. The VFO >>>> frequency drifts up at a rate of about 30Hz/minute (after a 5 minute >>>> warm >>>> up). Even after one hour, the drift is still about 15Hz/minute. This is >>>> too much, obviously. >>>> >>>> I have been trouble shooting this with the help of Gary, AB7MY. So far I >>>> have done the following: >>>> >>>> * Removed C2 to isolate D3 from the rest of the VFO circuit. No change. >>>> * Replaced all three VFO poly caps (one at a time). See above. >>>> >>>> I was wondering if anybody had any ideas on how to further trouble-shoot >>>> and resolve this issue... >>>> >>>> Thanks in advance and 73, >>>> >>>> -Matt / W6ZBA >>>> >>>> >> ______________________________________________________________ >> Elecraft mailing list >> Home: http://mailman.qth.net/mailman/listinfo/elecraft >> 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 >> >> ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft 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
