Source of 3-gang airspaced variable capacitors - UK Vintage Radio Repair and Restoration Discussion Forum

Alan_G3XAQ · 19th Jan 2021, 1:06 pm

I'm looking for three matching 3-gang variable capacitors at 350pF or more per section. 10pF minimum would be nice too, but I'm being picky. A 3-gang version of the Jackson OO (call it OOO?) would be ideal. Tracking accuracy between sections is not important.

I'd prefer new old stock and parts that weigh less than half a kilo but I'll take what is available. I've hunted t'internet to no avail. Any leads would be much appreciated.

Alan

Kentode · 19th Jan 2021, 4:18 pm

Try a phone call to Birkett's in Lincoln. If they have them they'll be good nos and a fair price.

Hope this helps.

Ed_Dinning · 19th Jan 2021, 7:21 pm

Hi Alan, I may have one or 2, but you might have to multi source for that many.

What is the project or are you starting a production run

Ed

Alan_G3XAQ · 19th Jan 2021, 8:22 pm

Thanks, I'll give Birkett a call tomorrow, though I suspect he may be closed at the moment with lockdown.

I'm thinking about (only thinking about) making a receiver preselector covering 1.8MHz to 30MHz, using the usual inductive bottom coupling. Inside a circuit simulator the span can be covered in two ranges with 365pF to 10pF variable capacitors but I suspect parasitic reactances will muck it up so three ranges seems safer. So three ganged capacitors for the three ranges. To achieve my target image suppression I need 3 tuned circuits for each range, hence my wanting three of these 3-gang capacitors.

And yes, it is back to front compared to the usual mechanically-tracked preselector. It seems to me that having servo-driven capacitors offers the option of a microprocessor controlled tuning system with individual peaking of each tuned circuit. Radio-control type servos are a well developed product these days.

I'm about to try out the twin-gang two-range approach as an experiment. If it really will tune over a 4:1 frequency range then I won't need to search for these hard-to-find 3-gang beasties.

Well, maybe.

Alan

19th Jan 2021, 1:06 pm	#1
Alan_G3XAQ Pentode Join Date: Apr 2018 Location: Canterbury, Kent, UK. Posts: 142	Source of 3-gang airspaced variable capacitors I'm looking for three matching 3-gang variable capacitors at 350pF or more per section. 10pF minimum would be nice too, but I'm being picky. A 3-gang version of the Jackson OO (call it OOO?) would be ideal. Tracking accuracy between sections is not important. I'd prefer new old stock and parts that weigh less than half a kilo but I'll take what is available. I've hunted t'internet to no avail. Any leads would be much appreciated. Alan

19th Jan 2021, 4:18 pm	#2
Kentode Heptode Join Date: Mar 2015 Location: Todmorden, West Yorkshire, UK. Posts: 574	Re: Source of 3-gang airspaced variable capacitors Try a phone call to Birkett's in Lincoln. If they have them they'll be good nos and a fair price. Hope this helps. __________________ Regards, Ken. BVWS member

19th Jan 2021, 7:21 pm	#3
Ed_Dinning Dekatron Join Date: Jan 2004 Location: Newcastle upon Tyne, Tyne & Wear, UK. Posts: 6,571	Re: Source of 3-gang airspaced variable capacitors Hi Alan, I may have one or 2, but you might have to multi source for that many. What is the project or are you starting a production run Ed

19th Jan 2021, 8:22 pm	#4
Alan_G3XAQ Pentode Join Date: Apr 2018 Location: Canterbury, Kent, UK. Posts: 142	Re: Source of 3-gang airspaced variable capacitors Thanks, I'll give Birkett a call tomorrow, though I suspect he may be closed at the moment with lockdown. I'm thinking about (only thinking about) making a receiver preselector covering 1.8MHz to 30MHz, using the usual inductive bottom coupling. Inside a circuit simulator the span can be covered in two ranges with 365pF to 10pF variable capacitors but I suspect parasitic reactances will muck it up so three ranges seems safer. So three ganged capacitors for the three ranges. To achieve my target image suppression I need 3 tuned circuits for each range, hence my wanting three of these 3-gang capacitors. And yes, it is back to front compared to the usual mechanically-tracked preselector. It seems to me that having servo-driven capacitors offers the option of a microprocessor controlled tuning system with individual peaking of each tuned circuit. Radio-control type servos are a well developed product these days. I'm about to try out the twin-gang two-range approach as an experiment. If it really will tune over a 4:1 frequency range then I won't need to search for these hard-to-find 3-gang beasties. Well, maybe. Alan