[R-390] VFO endpoint adjustment - stumped!

[DW Holtman]

Take a look at this link, it will give you an idea of the inner workings 
of the Cosmos PTO.

http://www.davemed.com/cosmos.html

I think most RF decks havea lot of  bad 2.2K resistors. Most of the 
tubes in the RF Deck have 2.2K resistors as plate loads such as V202 and 
V204 with the plate current going through them.

73's
DW Holtman
WB7SSN.


Tim Shoppa wrote:

>DJED1 at aol.com wrote:
>  
>
>>Sounds like you have a Cosmos PTO with the linearization adjustment.   The 
>>end point adjustment is to the RIGHT of the linearity adjustment, hidden partly 
>>behind the transformer housing.   However, you're only going to move the PTO 
>>tuning range a few KHz with the endpoint adjustment.   If you're off 50 KHz you 
>>either have a problem with the mechanical stops or with the PTO capacitors.   
>>Is the mechanical stop you're hitting within the PTO itself or the 10-turn 
>>stops in the radio?   You can change the realtionship of the PTO and 10-turn 
>>stop simply by loosening the shaft clamp on the PTO and turning it without 
>>adjusting the radio's geartrain.
>>    
>>
>
>Ed - it's something inside the PTO. The PTO has not been reattached
>to the Oldham coupler since the day I got this radio :-).
>
>But I will take your advice that it's gotta be something mechanical
>inside the PTO. The endpoint (I would call it the slope, but everyone
>else calls it the endpoint) and linearization are great, it's just that
>it doesn't go down to 2.455Mc but makes this mechanical scrape inside,
>most of a turn short.
>
>And a word to everyone: never ever trust a 2.2K 1/2W carbon resistor
>you see in a R-390A. I started investigating in my other radio (which
>had seen much better treatment over the years) and all of its 2.2K's
>were too high by a couple hundred percent too!
>
>Tim.
>_____________________________________________________________
>R-390 mailing list
>Home: http://mailman.qth.net/mailman/listinfo/r-390
>Help: http://mailman.qth.net/faq.htm
>Post: mailto:R-390 at mailman.qth.net
>Unsubscribe: http://mailman.qth.net/mailman/options/r-390
>
>
>  
>