[R-390] VFO squirreliness solved FOR GOOD

[Tim Shoppa]

DJED1 at aol.com wrote:
> entire threaded shaft.  I also resoldered the small  caps as Les had 
> suggested.  I put it in the radio tonight, and it tunes  great- no warbles.  The only 
> problem I have is that it's off about 2 Kc  end-to-end, and the variation is 
> not linear.  I'll tweak the end point and  see how close I can come- it will 
> probably meet the original specs when  completed, but won't be as good as a 
> tweaked Cosmos.
> Speaking of which, I also tweaked the end point on the Cosmos because it  was 
> out by 1 Kc.  Fixed that right up, but now intermediate points are out  by as 
> much as 1.8 Kc, where they were within 0.4 before I touched it.  And  the 
> strange thing is that all the 25Kc points are off the same amount- 1.8  Kc.  All 
> the 100 Kc points are right on, and the 75 Kc points are out about  0.8 Kc, 
> and also all the same.  Very strange.  I'll look at the data  tomorrow and 
> decide if I want to tweak all those little screws, or just put the  end point 
> adjustment back to where it was.  

The endpoint adjustment does interact at least a little with the calibration.

A couple kc is the limit of adjustment possible with the little
linearity screws.

I think that in some cases it may be wiser to add some small amount
of capacitance rather than tweak the endpoint. Maybe I'll experiment
with that tomorrow, AFTER replacing the toilet AND seeding the lawn AND
installing the ceiling fan... (meaning it probably won't happen!)

> While I was in the radio, I found I had a bunch of BBODs in the IF.  I  
> thought I had all Vitamin Q metal caps, but I was mistaken.  I don't have a  full 
> set of replacements, but I did replace C553 with an Orange Drop, so at  least 
> that is taken care of.

Was C553 a BBOD? The IF decks I've owned had BBOD's in a lot of not-so-
critical-for-leakage places (e.g. screen and filament bypasses) but better
quality metal cans - Vitamin Q's or Westcaps - at the filters.

Tim.