[ARC5] Radios and the Canal - Hammarlunds

[Geoff]

> On 17 May 2013 at 20:25, Richard Knoppow wrote:
>
>>    The cap appears in the schematic for the SP-400 on BAMA.
>> Its across the main tuning capacitor.  The handbook
>> identfies it as a compensating cap but does not give a value
>> for either capactance or temperature coefficient.  Carl
>> mentioned it in a long ago post so I am sure he knows the
>> details.
>
> As I said, it is a 3.3 pfd cap with at least an N-750 tempco. According to 
> the
> Hammarlund engineer, the cap should have "as high a negative temperature
> coefficient as one can find." which seems a bit non-specific to me.
>
> It is connected, under the capacitor shield, from the stator of the 
> oscillator
> section of that capacitor to ground.
>
> Re-peaking the oscillator trimmers will be required.
>
> Ken W7EKB


N1500 was a fairly common value, Ive used a few that I could find around 
here or N750 depending upon drift and how much C could be added before dial 
tracking became an issue.

And as I said earlier you start at the tuning cap to stabilize the highest 
range and then add others for the lower ranges as needed as each ranges 
added TC cap will be in parallel with the common one.
There was a Hammarlund issued bulletin for this that I have around here 
somewhere, maybe as an addendum to the first run SP-400.

Carl