[ARC5] R-25 dial nonlinearities

[Clare Owens]

The math in this article is somewhat beyond my somewhat ancient brain but
perhaps it might inspire some of you younger folks:

http://www.robkalmeijer.nl/techniek/electronica/radiotechniek/hambladen/hr/1990/01/page53/

In any case it looks interesting...

Clare  N2RJB

On Sun, Jan 8, 2017 at 2:27 PM, Richard Knoppow <1oldlens1 at ix.netcom.com>
wrote:

>    Capacitor plate shape is covered in many older engineering books. I
> will see if I can generate a list.  Many older books are available on line
> from tubebooks.org and archive.org   These are free.
>    Variable caps used to be available in three or four standard types:
> Straight line capacitance, straight line wavelength, straight line
> frequency and compromise. Straight line frequency requires that the plat
> shape be rather extreme so were not very often used.  Receivers mostly used
> "mid-line" caps which provided some extension on the low capacitance side
> in order not to compress the high end dial too much but still retain a more
> practical plate shape.
>     One thing to look for when the dials seem far out of calibration is
> the centering of the rotor.  The variation in capacitance changes when the
> rotor is off center and is not linear.  At the center the capacitance is
> minimum. Remember the capacitance is a square law function of area so the
> change in variation with spacing is somewhat critical. If you can measure
> the capacitor on a bridge you can adjust the end bearings to get it exactly
> centered.  This is assuming that no serious plate bending has been done.
> Plate bending is legit on some devices and not on others. For instance, the
> handbook for the Hewlett-Packard 200CD oscillator gives specific
> instructions for bending the plates (but the factory bending should usually
> be left alone) while in the Hammarlund SP-600-JX the plates should NEVER be
> bent. If they are you can never get the dial to track.
>     I would suggest looking at the cap in the R-25 to see if its correctly
> centered. I don't know whether they are supposed to have bent plates.
>
> On 1/8/2017 10:55 AM, Mike Everette via ARC5 wrote:
>
>> Gordon White wrote:
>>
>>
>>     Unfortunately I did not hear that he had died until his heirs tossed
>> out his design notebooks.
>>
>>
>> And so, more knowledge and history is lost forever.
>>
>> Guys, if you have stuff like this, please please PLEASE make sure
>> someone in your family knows its value and significance.
>>
>> 73
>>
>> Mike
>>
>> WA4DLF
>>
>>
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> --
> Richard Knoppow
> 1oldlens1 at ix.netcom.com
> WB6KBL
>
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