Freeing off a Jackson C804 variable capacitor - UK Vintage Radio Repair and Restoration Discussion Forum

Alan_G3XAQ · 8th Jun 2020, 9:29 pm

I'm using a Jackson C804 capacitor for the main tuning in a simple receiver

http://www.royalsignals.org.uk/jackson_bros_caps/c8.htm

Yes, I know I should have used a proper double ball race variable capacitor but I didn't have one in the drawer.

It seems stable enough when I thump the radio but really it's a bit too stable in as much as the shaft needs more turning torque than I'd like. As far as I can see the bush isn't adjustable. Before I try applying some watch oil with a pointed matchstick and perhaps afterwards regret it, has anyone tried lubricating this type of non-ballrace capacitor to make it turn a little bit more freely?

Thanks, Alan

M0FYA Andy · 8th Jun 2020, 9:39 pm

As a trimmer it was probably designed to be stiff to avoid inadvertent movement.

Andy

Bazz4CQJ · 8th Jun 2020, 11:33 pm

Although the catalogue calls them all "trimmers", clearly, the ones which can accept a knob may be used as front panel controls. I don't think I've previously encountered one that was a problem. I cannot see why a trace of lubricant should be an issue; maybe the silver plating will show some tarnish but many of the old ones do anyway.

B

Jon_G4MDC · 9th Jun 2020, 8:53 am

Give it graphite instead of oil first?

Alan_G3XAQ · 14th Jun 2020, 8:59 pm

Applying lubrication didn't help.

There is a spring clip at the back of the ceramic insulation that carries the earth tag but also pulls the rotor assembly into the bush on the front. A (very) gentle tweak with a pointed stick to slightly bend the clip and reduce the clamping pressure has solved my problem.

Yes it's a one way street but a series of small tweaks while checking the required torque until it turned freely but with no end play gave me the desired result.

73, Alan G3XAQ

8th Jun 2020, 9:29 pm	#1
Alan_G3XAQ Pentode Join Date: Apr 2018 Location: Canterbury, Kent, UK. Posts: 189	Freeing off a Jackson C804 variable capacitor I'm using a Jackson C804 capacitor for the main tuning in a simple receiver http://www.royalsignals.org.uk/jackson_bros_caps/c8.htm Yes, I know I should have used a proper double ball race variable capacitor but I didn't have one in the drawer. It seems stable enough when I thump the radio but really it's a bit too stable in as much as the shaft needs more turning torque than I'd like. As far as I can see the bush isn't adjustable. Before I try applying some watch oil with a pointed matchstick and perhaps afterwards regret it, has anyone tried lubricating this type of non-ballrace capacitor to make it turn a little bit more freely? Thanks, Alan

8th Jun 2020, 9:39 pm	#2
M0FYA Andy Nonode Join Date: May 2007 Location: Preston, Lancashire, UK. Posts: 2,511	Re: Freeing off a Jackson C804 variable capacitor As a trimmer it was probably designed to be stiff to avoid inadvertent movement. Andy

8th Jun 2020, 11:33 pm	#3
Bazz4CQJ Dekatron Join Date: Apr 2009 Location: Oxfordshire, UK. Posts: 4,935	Re: Freeing off a Jackson C804 variable capacitor Although the catalogue calls them all "trimmers", clearly, the ones which can accept a knob may be used as front panel controls. I don't think I've previously encountered one that was a problem. I cannot see why a trace of lubricant should be an issue; maybe the silver plating will show some tarnish but many of the old ones do anyway. B __________________ Saturn V had 6 million pounds of fuel. It would take thirty thousand strong men to lift it an inch.

9th Jun 2020, 8:53 am	#4
Jon_G4MDC Nonode Join Date: Nov 2015 Location: Welwyn Garden City, Hertfordshire, UK. Posts: 2,015	Re: Freeing off a Jackson C804 variable capacitor Give it graphite instead of oil first?

14th Jun 2020, 8:59 pm	#5
Alan_G3XAQ Pentode Join Date: Apr 2018 Location: Canterbury, Kent, UK. Posts: 189	Re: Freeing off a Jackson C804 variable capacitor Applying lubrication didn't help. There is a spring clip at the back of the ceramic insulation that carries the earth tag but also pulls the rotor assembly into the bush on the front. A (very) gentle tweak with a pointed stick to slightly bend the clip and reduce the clamping pressure has solved my problem. Yes it's a one way street but a series of small tweaks while checking the required torque until it turned freely but with no end play gave me the desired result. 73, Alan G3XAQ