Johnson & Matthey: resistance wire book - UK Vintage Radio Repair and Restoration Discussion Forum

John_BS · 17th Feb 2016, 3:11 pm

Another scan for posterity; dated 1952. Some alloys I've never heard of!

John

pmmunro · 18th Feb 2016, 6:15 pm

John,

Many thanks for taking the trouble to scan and post this interesting and useful information.

I will be filing it for future consultation.

PMM

18th Feb 2016, 6:36 pm

The Colvern 'Cam corrected precision potentiometer' is marvellous, I want one just to fiddle with. A mechanical look up table, bet that was fun to adjust.

TonyDuell · 18th Feb 2016, 7:52 pm

I have a couple of cam-corrected potentiometers in ex-miliatary/aircraft units (not quite sure what they came from, they have differential gearing to the pot, with the inputs coming from a stepper motor and (in one unit) a hand control or (in the other) a DC motor.

They are quite interesting, there is a cam ring with many screws round it, so that adjusting the screws causes the ring to slightly distort (up and down) forming the cam surface. The rotor has the moving contact on a sort of linkage arangement so that the cam moves it sideways slightly. The idea is to correct for non-linearity in the wirewound 'track' by moving the contact to correct for this.

18th Feb 2016, 6:15 pm	#2
pmmunro Octode Join Date: Jul 2004 Location: Dundee, UK. Posts: 1,813	Re: Johnson & Matthey: resistance wire book John, Many thanks for taking the trouble to scan and post this interesting and useful information. I will be filing it for future consultation. PMM

18th Feb 2016, 6:36 pm	#3
Guest Guest Posts: n/a	Re: Johnson & Matthey: resistance wire book The Colvern 'Cam corrected precision potentiometer' is marvellous, I want one just to fiddle with. A mechanical look up table, bet that was fun to adjust.

18th Feb 2016, 7:52 pm	#4
TonyDuell Dekatron Join Date: Jun 2015 Location: Biggin Hill, London, UK. Posts: 5,215	Re: Johnson & Matthey: resistance wire book I have a couple of cam-corrected potentiometers in ex-miliatary/aircraft units (not quite sure what they came from, they have differential gearing to the pot, with the inputs coming from a stepper motor and (in one unit) a hand control or (in the other) a DC motor. They are quite interesting, there is a cam ring with many screws round it, so that adjusting the screws causes the ring to slightly distort (up and down) forming the cam surface. The rotor has the moving contact on a sort of linkage arangement so that the cam moves it sideways slightly. The idea is to correct for non-linearity in the wirewound 'track' by moving the contact to correct for this.