Ed Palmer wrote: > Hi Paul, > > Did you see this page that talks about tweaking the 10811 oven controller? > > http://www.realhamradio.com/z3801a-turning-point.htm > > Ed >
Although this article anecdotally claims success, it overlooks a number of important issues. First of all, a large proportion of 10811 crystals DO NOT HAVE A TURNOVER. They merely have a very low TC around 82 degrees. It is ALWAYS 82 degrees for these crystals. The crystals that do, technically, have a turnover, still have very low TC even if the oven is slightly off the turnover. Secondly, the tempco of the electronics, specifically the selected 2N5179 oscillator transistor, is a significant player. The thermal gain, if properly adjusted, is around 1000 at the crystal, but is much less at the oscillator transistor. It may very well be the dominant factor in overall oscillator tempco. Possibly, if you have a crystal with a turnover, you should deliberately operate off the turnover at a point where the crystal drift cancels the drift of the electronics. If you want to tweak a 10811, you should also tweak the thermal gain by custom adjustment of the heat balancing resistors for the heater transistors. This has to be done by converting the oscillator to mode B and then converting it back to mode C afterwards. Rick Karlquist N6RK _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
