[Elecraft] OT - Source for Air Variable Capacitors

[Walter Underwood]

For a magnetic loop, the contact resistance of the wipers on typical air variable capacitors causes big losses. That is why he’s specifically looking for vacuum, butterfly, or split stator variable capacitors.

The MFJ butterfly capacitors are reasonably priced, at $70 and $90. MFJ uses them in the mag loop tuners they sell.

wunder
K6WRU
Walter Underwood
CM87wj
http://observer.wunderwood.org/ (my blog)

> On Jun 16, 2018, at 9:13 PM, Josh Fiden <josh at voodoolab.com> wrote:
> 
> These look interesting & $38 incl shipping. I'd be inclined to check this out before MFJ..
> 
> https://m.ebay.com/itm/High-Voltage-Air-Variable-Capacitors-20-95pF-Amplifier-Tuner-REPAIR-DIY-/161247381436
> 
> 73
> Josh W6XU
> 
> Sent from my mobile device
> 
>> On Jun 16, 2018, at 7:34 PM, K9MA <k9ma at sdellington.us> wrote:
>> 
>> I searched far and wide for high voltage air variables a year or so ago for a tuner.  I needed some quite specific values rated up to about 1 kV.  The only place I could find them was Surplus Sales of Nebraska.  They weren't cheap.
>> 
>> 73,
>> Scott K9MA
>> 
>> 
>>> On 6/16/2018 20:30, rich hurd WC3T wrote:
>>> I bought a Cardwell 500PF 3.5KV on eBay last year.  As a bonus I discovered
>>> that it had a reduction drive when I opened the box.  :)
>>> 
>>> Not sure if it fits your requirements - it's pretty ratty looking, and was
>>> obviously pulled from some electronic equipment.   I sort of resigned
>>> myself to needing to 'spiff it up'.
>>> 
>>> Keep your eyes open on eBay, that's the best advice I can offer.
>>> 
>>>> On Sat, Jun 16, 2018 at 8:05 PM Dauer, Edward <edauer at law.du.edu> wrote:
>>>> 
>>>> With the tutelage of a friend I am putting together a mag loop but have
>>>> had no luck finding a source of air variable capacitors up to the task.
>>>> Vacuum variables aren’t hard to find, but the $200 and up price tag is
>>>> offputting.  I have seen a couple of AVCs on E-bay that looked pretty
>>>> ratty; and the commercial types for sale new look like low-power trimmers.
>>>> Anyone know of a source --  or even have any they’d sell?  Specifically I
>>>> would like a range of 6 to 120 pf or more, butterfly or split stator, with
>>>> plate spacing sufficient to take a kilovolt of RF.  And ideally with
>>>> reduction gear tuning though that’s optional.
>>>> 
>>>> Thanks for any info anyone can provide . . .
>>>> 
>>>> Ted, KN1CBR
>>>> 
>>>> ______________________________________________________________
>>>> Elecraft mailing list
>>>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>>>> Help: http://mailman.qth.net/mmfaq.htm
>>>> Post: mailto:Elecraft at mailman.qth.net
>>>> 
>>>> This list hosted by: http://www.qsl.net
>>>> Please help support this email list: http://www.qsl.net/donate.html
>>>> Message delivered to rich at wc3t.us
>> 
>> -- 
>> Scott  K9MA
>> 
>> k9ma at sdellington.us
>> 
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Elecraft at mailman.qth.net
>> 
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to josh at voodoolab.com
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to wunder at wunderwood.org