Eddy -
Here is a little more elaborate article, including the rectification and regulation of the LMO _AND_
the BAND oscillator filament supply.
The fact that there is a 'delay' in the drift suggests filament voltage is at least a possible
factor. The R-44 is the only 4 Line unit that has a tube LO, so that may be why there was no more
investigation of the problem. Certainly dropping the filament voltage on an oscillator produces a
frequency shift as the gain drops. A "NEW" tube will be affected less due to the excess cathode
emission of a new tube, so just keeping a newer tube in there might solve the problem, or at least
reduce it. The BAND oscillator shift is also possible in the R-4, as that is also a tube stage.
You may be 'chasing your tail', but it would be an interesting experiment, and the required parts
are very cheap these days!
73, Garey - K4OAH
Glen Allen, VA
Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line
and TR-4/C Service Supplement CDs
<www.k4oah.com>
Diane and Edward Swynar wrote:
*/Hi Guys,/*
Per chance, does anyone reading this have any recollection as to the
/_QST_ // "/Hints & Kinks/" edition which made reference to
/regulating/ the 6.3 heater volts of the 6AU6 VFO tube in the Heathkit
SB-300/301 receiver...?
I have the very same malady, I'm sure, plaguing my R-4 receiver.
The station with the /Drake Twins/ is located right between the sump
room & the forced air electric furnace of the basement: whenever
either (_A_) the furnace, or (_B_) the sump pump, or (_C_) the well
water pump kicks in, the CW station I'm listening to will slowly start
to drift a second, or two, after said device starts. Once the unit
kicks off, the CW signal will return to "normal", again, after the
prescribed second, or two.
I suspect that unregulated heater voltage is affecting the PTO
frequency, just as it did in the referenced Heath receivers...
The "cure" in that instance (per that now-forgotten "/Hints & Kinks/"
piece) was the incorporation of rectifier, small electrolytic
capacitor, & a zener diode at the filament supply of the VFO tube...
Ring any bells with anybody...?
*/~73~ de Eddy VE3CUI - VE3XZ/*
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