[HBR] Negative temp compensation capacitors

[Tim Shoppa]

W6HHT asks:

> Has anyone on the reflector identified a source for negative temp 
> coefficient capacitors in the N750 range available in small capacitance 
> ranges (e.g., 1 pfd through 20 pfd in 1  and 2 pfd steps)?  I am aware 
> of one US  manufacturer (Presidio Products) making a wide range of those 
> components, but apparently only through contract with defense and 
> aerospace manufacturers, nothing available (according to their local 
> rep) through distributors or mail-order houses (Newark et al).

> These caps are used in the HBR 11/13 Hartley oscillator design to 
> stabilize frequency drift caused by temperature rise on start-up.

I just went to www.newark.com and searched for "n750" and
they seem to have some Vishay, Dale, Sprague, etc. N750
ceramic disk parts in stock in the 10pF -low hundred pF range.

Put a couple of these in series and you can synthesize any
value you want from low pF on up. I know, it's not as
nice having every pF value from 10 to 20 in a drawer.

Try widening your search so you don't just get Presidio.

Also, Digikey lists AVX and BC N750 parts in their database
as special order, when I've ordered similar parts in the past
it took "only" a few weeks to get them.

Allied lists some nominal-N750 tempco ceramic trimmers from AVX
and Murata which are not the perfectly traditional way of doing this
but are used for tempco trimming in more modern equipment.

Tim.