[Hammarlund] Accuracy

[James A. (Andy) Moorer]

I think you have leaky caps in the turrets. You don't have to invoke extreme 
rf - simple humidity and high temperatures will break the seals on those old 
mica caps. Once moisture gets in, bad things happen.

Note that the inductors in the turret can change value as well, also from 
humidity and temperature. They can MFP the outside of the coil, but not the 
ferrite itself. Ferrite is porus and will quite happily soak up any gunk 
that is in the air.

On most units, you can align all the bands dead on with ease and have 
adjustment to spare at both ends of the dial.

In between the top and bottom, all bets are off. The big variable capacitor 
isn't calibrated any more after 30 years. Moreover, you and I can't align 
it. It requires a custom jig that compares one section to the next and 
measures the capacitance. We had an email a few years ago from a lady that 
actually aligned these capacitors for Hammarlund. She said that she had a 
hand-wired pile of electronics connected to the capacitor. She would adjust 
the vanes one by one to make them all the same capacitance. She said she 
could do three of them a day.

One of these days, maybe I'll sit down with a precision capacitance bridge 
and try my hand at adjusting it, but only if I have a lot of time to kill . 
. .

James A. (Andy) Moorer
www.jamminpower.com


----- Original Message ----- 

>I may be shooting for something that is not possible to achieve.  I had to 
>do a little engineering to get the 3.45 - 7.4 mc band to align properly and 
>now I am wondering if I am asking too much.  The dial appears to be laid 
>out very accurately, but I am getting some weird results.  The top and 
>bottom are perfect and many of the stops in between are also on the money. 
>However, some are as much a full mark off.  Is this normal or have I still 
>got problems?  I realize with the dial graduated the way it is it will be 
>necessary to use the logging scale to achieve any type of accuracy, but it 
>seems the main dial should be on at least on the numbered marks.  Am I 
>shooting for the impossible or should I keep on trying?
> I had to change the capacitance in the turret module to get the oscillator 
> to align.  The other bands I have tried will also need similar attention. 
> Do you think it possible the rf/oscillator section was exposed to extreme 
> rf and caused a problem with the coil(s)?
> Thanks,
> Rick/K5IZ
>