[R-390] VFO end point off 17 KHz

[David Olean]

Hello Mr. Bottled Water, (Perrier)

OK on all the advice. It sure does sound like there is something wrong, 
but with ferrites that are 50+ years old, you can get some significant 
drift too. I have an old 144 MHz Tecraft xmtr from my boyhood that had 
all the slugs drift so far down that it stopped working. I had to modify 
all of the multiplier coils to get it back on 24 and 72 MHz.  That is a 
pretty drastic change.  That is what prompted me to diddle with the end 
point coil. So now it is working great with nice linearity across 950 
kHz and only 500 Hz off at one end.  I'll come back to this problem 
soon.  Getting the PTO out is sorta simple, so I will order some new 
capacitor parts and come back to it on some cold winter night. In the 
mean time, I am re aligning the entire set and fixing a few problems. 
The carrier meter has stopped working and the RF gain control is acting 
funny. This R-390A had the antenna relay removed and an (ugh) SO-239 
connector installed in its' place. I just bought a relay and am looking 
for the wires to re install it, but can't find them ?  I am not sure, 
but think they must have been clipped and removed. I'll run new wires to 
the rectifier and get it all working.

I also found that the 15.000 MHz crystal has died.  This only affects 
the 27 MHz band.  It will not oscillate, or if it does, it is very weak. 
I need a replacement crystal. I found a 7.500 MHz one in my junque box 
and it actually works, but output is a bit low and injection is not 
enough.  Fair Radio does not list any. I am looking for a replacement.

If anyone has a Cosmos PTO I would be interested in getting another one 
to work with as well.  They do get addicting.

73 Dave K1WHS


On 11/2/2019 5:42 AM, Perry Sandeen via R-390 wrote:
> Yo Bubba Dudes!,
> I agree about returning the end point coil to its original 3 turns.  I disagree with fixing the drift with adding caps.
> With that amount of drift there is something wrong with one or more of the OEM caps. As you said they're 50 plus years old. IMNSHO, you should shotgun the caps a well as the resistors using 1% MF replacements. Even in small quantities there about 25 cents each from Mouser with no minimum order.
>
>   Members are reporting that tiny silver migration is causing havoc with old SM caps that test OK.
>    Dan's Small Parts carries a nice selection stating at 1pF so you can get just what you need with series and/or parallel combinations. You'll probably still need a N200 cap as well. Fixing PTO's is as much art as science with patience being your best tool.
> Regards,
> Perrier
>
>
>
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