Air-dielectric variable capacitors

[David Murphy]

Hey folks. I've had my license for just a couple of weeks now. The only
equipment I have at the moment is a Ramsey 2m receiver kit I bought years
ago. Largely for economic reasons, I'm attempting to build a 40m SSB
receiver from schematics in the ARRL Handbook. The first item I'm looking
for is the tuning capacitor. I searched through the list of distributors
from ARRL's site, and found some candidates in Antique Electric Supply's
catalog. Here are the notes:

* Ball bearing mounted shaft
* Gear drive vernier
* 1/4" flatted shaft
* Body is 1-1/4" high x 1-1/8" wide by 1-7/8" long.
* 15 plate section @ 200 pf with trimmer
* 5 plate section @ 30 pf with trimmer
* 13 plate section @ 85 pf with trimmer
* 5 plate section @ 25 pf (no trimmer)

They're priced right ($6 each), but I'm brand new to this, so I want to
verify that I can use these. The schematic calls for a 30pF cap. For
multi-section caps like these, are the sections isolated from each other
to effectively be their own component? In other words, can I just hook up
the 30pF 5-plate section and leave the rest alone? (And for future
reference, could I hook multiple sections in parallel to create additional
capacity possibilities?)

Thanks,
David Murphy
AB8SO

[Dave Platt]

>* Ball bearing mounted shaft
>* Gear drive vernier
>* 1/4" flatted shaft
>* Body is 1-1/4" high x 1-1/8" wide by 1-7/8" long.
>* 15 plate section @ 200 pf with trimmer
>* 5 plate section @ 30 pf with trimmer
>* 13 plate section @ 85 pf with trimmer
>* 5 plate section @ 25 pf (no trimmer)
>
>They're priced right ($6 each), but I'm brand new to this, so I want to
>verify that I can use these. The schematic calls for a 30pF cap. For
>multi-section caps like these, are the sections isolated from each other
>to effectively be their own component?

Typically they have one set of plates in common (usually the ones
attached to the rotating stator). Each section has a second set of
plates, insulated from the frame and from the other sections.

> In other words, can I just hook up
>the 30pF 5-plate section and leave the rest alone?

Yes - use the (common) stator connection, and the connection
for that one section's isolated plates. There may be a very small
amount of parasitic capacitance between the section you're using and
other sections - it's probably not enough to matter in any way.

> (And for future
>reference, could I hook multiple sections in parallel to create additional
>capacity possibilities?)

Yes.

--
Dave Platt > AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

[Dave Platt]

>* Ball bearing mounted shaft
>* Gear drive vernier
>* 1/4" flatted shaft
>* Body is 1-1/4" high x 1-1/8" wide by 1-7/8" long.
>* 15 plate section @ 200 pf with trimmer
>* 5 plate section @ 30 pf with trimmer
>* 13 plate section @ 85 pf with trimmer
>* 5 plate section @ 25 pf (no trimmer)
>
>They're priced right ($6 each), but I'm brand new to this, so I want to
>verify that I can use these. The schematic calls for a 30pF cap. For
>multi-section caps like these, are the sections isolated from each other
>to effectively be their own component?

Typically they have one set of plates in common (usually the ones
attached to the rotating stator). Each section has a second set of
plates, insulated from the frame and from the other sections.

> In other words, can I just hook up
>the 30pF 5-plate section and leave the rest alone?

Yes - use the (common) stator connection, and the connection
for that one section's isolated plates. There may be a very small
amount of parasitic capacitance between the section you're using and
other sections - it's probably not enough to matter in any way.

> (And for future
>reference, could I hook multiple sections in parallel to create additional
>capacity possibilities?)

Yes.

--
Dave Platt > AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!

[Steve Nosko]

"David Murphy" > wrote in message
...
> Hey folks. I've had my license for just a couple of weeks now. The only
> equipment I have at the moment is a Ramsey 2m receiver kit I bought years
> ago. Largely for economic reasons, I'm attempting to build a 40m SSB
> receiver from schematics in the ARRL Handbook. The first item I'm looking
> for is the tuning capacitor. .....

Try Dan's for parts. He shows a lot of older type parts.

http://www.danssmallpartsandkits.net/


--
Steve N, K,9;d, c. i My email has no u's.

[Steve Nosko]

"David Murphy" > wrote in message
...
> Hey folks. I've had my license for just a couple of weeks now. The only
> equipment I have at the moment is a Ramsey 2m receiver kit I bought years
> ago. Largely for economic reasons, I'm attempting to build a 40m SSB
> receiver from schematics in the ARRL Handbook. The first item I'm looking
> for is the tuning capacitor. .....

Try Dan's for parts. He shows a lot of older type parts.

http://www.danssmallpartsandkits.net/


--
Steve N, K,9;d, c. i My email has no u's.

[Reg Edwards]

In some applications the working or breakdown voltage may matter.

Don't forget the working or breakdown volts, or the spacing between plates.
---
Reg G4FGQ

[Reg Edwards]

In some applications the working or breakdown voltage may matter.

Don't forget the working or breakdown volts, or the spacing between plates.
---
Reg G4FGQ