Air-dielectric variable capacitors
 

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

* 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!

* 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!

"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.

"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.

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

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