[R-390] Need value of R235 from a RF deck

[Flowertime01 at wmconnect.com]

Craig,

I am not finding R235 on my R390/A TM schematic.

The crystal calibrator isn't quite right! If I use the
trimmer to zero beat WWV life is good until I turn the calibrator off or
switch to a different band. Then the calibration is as much as 20-30 KC's
off. 

When you change bands you are using a different set of crystals from the 
mixer sections. Any one of the second mixer crystals can be off by any amount.

That's the whole idea of having a crystal to beat against and reset the dial 
readout 
with the zero adjust.

But if you were just to switch the MC band up and down and come back to WWV 
without changing the KV knob or the zero adjust, you would expect WWV to still 
be close to zero beat (close being under a couple 100 hertz).

Common problems these days are the ground points. The little screws have 
caught crud after 50 plus years. You just need to loosen the bolts and nut up a 
turn or two and retighten the bolt and nut to reset the connection. Any one of 
these ground lugs on the end of a resistor or coupling cap can form a variable 
resistance that causes problems.  You likely have one of these in the 
calibration section that is giving you drift. Every time you turn the calibrator on 
you surge a current through that one crud connection and its instant resistance 
changes. Just enough to yield a different frequency from the calibration 
oscillator.

Good Luck with this. It is repairable. It just will just take some effort.


Roger AI4NI   </HTML>