[R-390] VFO End points

[Gordon]

Roger,
I did the End point adjustment and have it down to just under 1kc 
(900hz) off from end to end. I had to adjust the coil clockwise.
  I have run into where any more clockwise adjustment makes NO more 
change. I assume I must open the VFO and remove one turn from the coil ?
I have the adjustment set to exactly Zero on the low end and the top 
comes out to 900 hz past the 10 turns mark . (+ XX.000) and 900 hz. 
(Just under + XX.001)
Perhaps I should leave it be since it is so close now. Still, I'd like 
to have it exact..LOL
I noticed when I remove the outer cover on my Cosmos it has a Label 
warning me that it is under 15 pounds pressure from Dry Nitrogen. Is 
this something I need to be concerned with?
Also, Do you have to re-pressurize it ? I don't think I do from what I 
have read.


Gordon
N6WK


On 5/26/2013 3:30 PM, Roger Ruszkowski wrote:
>
> Gordon,
>   
> Three different adjustment on the VFO.
>   
> One is in the Oldham coupler to get the Gears, dial and VFO together.
>   
> Second is an end point band spread adjustment to get the VFO to span 1 meg over 10 turns exactly
>   
> Third is the  track inside the VFO can. It's a bit tedious. Unless its a cosmos in which case it's still a bit tedious.
>   
> As you find your  390A zero beats at +003  and at -997 so it is 3 high on one end and 3 low one the other. It is pretty
> close to dead on at the 500 Mark.
>   
> You need to do the end point adjust to get your band spread back to 1 meg over 10 turns
> A counter works best. You can do it on the calibration tones.
>   
> After you get the band spread reset, you will then need to reset the zero on the
> Oldham coupler as you reinstall the VFO.
>   
> Start in the Y2K manual at 6.2.16 End point Adjustment.
>
> A small screwdriver and a couple tries.
> If you start the right way it goes quickly.
> Changing the spread will move both end points.
> Do not try to hold the start stop point.
> Make an adjustment,
> Set one end to zero against the counter or the cal tone.
> Make a tick mark across the coupler face and the VFO face.
> Dial off ten turns exact.
> Listen to how close it is.
> Go back ten turns
> Make another adjustment and start over.
> You can get down to well under a 100 hertz total end to end error.
>
> If you run out of adjustment, before you get exact, STOP
> Do not force the adjustment.
>
> You can open the VFO further, and take a turn off the trim coil.
> Read about this in the Pearls if you need to go this route.
>
>
>   
> If you have no counter, and need to do this against the cal tones, post an e-mail I will
> write it up here so we can get it saved in the archives again.
>
> Roger AI4NI
>
>
>   
> ______________________________________________________________
> R-390 mailing list
> Home: http://mailman.qth.net/mailman/listinfo/r-390
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:R-390 at mailman.qth.net
>
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
>