Suggest a use for this wierd Colvern Pot. - UK Vintage Radio Repair and Restoration Discussion Forum

hugozair · 10th Mar 2020, 12:32 pm

This thing has been in my "might come in useful" box for ever - and it never has ! It's marked Colvern, 6610/22, 10KK, 7529.. It's 65mm dia and has no rotational end stop. 5 connections on the back of the metal case are arranged as a square with the 5th central and marked "E". diagonal opposite corners are marked + & - one way and S & C the other.
I've opened it up to see what happens inside.
There's a wirewound resitance on a flat, square paxolin former. connnected to + & - with centre tap to E.
There are two rotating wipers spaced 90 degrees apart (S & C ) bearing down on the flat resistance and wiping a circular track on the square ww resistance face..

I can't think of a single use..and have no idea where it came from..

So...if anyone ever reads this ...and recognises such a wierd thing..let me know please..

ronbryan · 10th Mar 2020, 12:56 pm

Sine/Cos pot used in radar rotating scan systems or servomechanisms?

Ron

Lucien Nunes · 10th Mar 2020, 1:41 pm

Indeed. If you have a dual trace scope, connect a few volts DC to + and - connect the two wipers to the two inputs w.r.t. G, run it at a nice slow auto scan and rotate the pot shaft steadily, to see two sine waves in quadrature appear on your screen.

G6Tanuki · 10th Mar 2020, 1:52 pm

Wasn't this - or something rather similar - used to produce the circular 'scan' on the screens of Radars, Sonars, fish-finders etc?

M0FYA Andy · 10th Mar 2020, 2:40 pm

I agree with the replies above.
I have come across this in the context of the ASV MkXI radar, fitted to Fleet Air Arm aircraft such as the Barracuda and Swordfish during WW2.
Whist most airborne radars of that era used a sine-cosine resolver type of Magslip to generate the rotating scan, ASV MkIX used a Slab Potentiometer, wound as described by the OP, although in an oil-filled casing about 5 inches in diameter.

Andy

M0FYA Andy · 10th Mar 2020, 2:48 pm

This a description from the radar manual.

Andy

10th Mar 2020, 7:42 pm

Fascinating, so simple. Everyday is a school day.

Tractorfan · 11th Mar 2020, 12:21 am

Hi,
How daft am I?

I always thought that the display on a radar display screen was produced by physically rotating the scan coils, fed via slip rings, around the neck of the CRT. Doh!
I shall take myself off and stand in the corner.

Cheers, Pete.

MeerKat · 11th Mar 2020, 12:30 am

You are not daft Tractorfan, I know some marine radars that do this!

Regards,

M0FYA Andy · 11th Mar 2020, 10:06 am

British wartime airborne radars typically used the ubiquitous VCR97, VCR138, VCR139 and VCR517 tubes, all electrostatically scanned.
Electromagnetic scanning came in post-war, and yes, one approach was to mechanically rotate the scanning coils.

Andy

hugozair · 11th Mar 2020, 11:05 am

Quote:

Originally Posted by M0FYA Andy

This a description from the radar manual.

Andy

Thank you all, especially Andy with that doc...I suppose it would have been used to give static S&C values...and not rotated by a motor to actually provide S&C waves...it would soon wear out....wouldn't it

So...it looks like I won't be finding a use for it any time soon,,,, Roger

hugozair · 11th Mar 2020, 12:08 pm

And finally...If anyone is ever in need of one of these rare items for a restoration project etc..It's available FOC

10th Mar 2020, 12:32 pm	#1
hugozair Triode Join Date: Jan 2010 Location: Penzance, Cornwall, UK. Posts: 34	Suggest a use for this wierd Colvern Pot. This thing has been in my "might come in useful" box for ever - and it never has ! It's marked Colvern, 6610/22, 10KK, 7529.. It's 65mm dia and has no rotational end stop. 5 connections on the back of the metal case are arranged as a square with the 5th central and marked "E". diagonal opposite corners are marked + & - one way and S & C the other. I've opened it up to see what happens inside. There's a wirewound resitance on a flat, square paxolin former. connnected to + & - with centre tap to E. There are two rotating wipers spaced 90 degrees apart (S & C ) bearing down on the flat resistance and wiping a circular track on the square ww resistance face.. I can't think of a single use..and have no idea where it came from.. So...if anyone ever reads this ...and recognises such a wierd thing..let me know please..

10th Mar 2020, 12:56 pm	#2
ronbryan Octode Join Date: Jan 2003 Location: Guildford, Surrey, UK. Posts: 1,960	Re: Suggest a use for this wierd Colvern Pot. Sine/Cos pot used in radar rotating scan systems or servomechanisms? Ron

10th Mar 2020, 1:41 pm	#3
Lucien Nunes Rest in Peace Join Date: Apr 2008 Location: London, UK. Posts: 2,508	Re: Suggest a use for this wierd Colvern Pot. Indeed. If you have a dual trace scope, connect a few volts DC to + and - connect the two wipers to the two inputs w.r.t. G, run it at a nice slow auto scan and rotate the pot shaft steadily, to see two sine waves in quadrature appear on your screen.

10th Mar 2020, 1:52 pm	#4
G6Tanuki Dekatron Join Date: Apr 2012 Location: Wiltshire, UK. Posts: 14,007	Re: Suggest a use for this wierd Colvern Pot. Wasn't this - or something rather similar - used to produce the circular 'scan' on the screens of Radars, Sonars, fish-finders etc?

10th Mar 2020, 2:40 pm	#5
M0FYA Andy Nonode Join Date: May 2007 Location: Preston, Lancashire, UK. Posts: 2,511	Re: Suggest a use for this wierd Colvern Pot. I agree with the replies above. I have come across this in the context of the ASV MkXI radar, fitted to Fleet Air Arm aircraft such as the Barracuda and Swordfish during WW2. Whist most airborne radars of that era used a sine-cosine resolver type of Magslip to generate the rotating scan, ASV MkIX used a Slab Potentiometer, wound as described by the OP, although in an oil-filled casing about 5 inches in diameter. Andy

10th Mar 2020, 7:42 pm	#7
Guest Guest Posts: n/a	Re: Suggest a use for this wierd Colvern Pot. Fascinating, so simple. Everyday is a school day.

11th Mar 2020, 12:21 am	#8
Tractorfan Dekatron Join Date: Mar 2008 Location: St. Frajou, l'Isle en Dodon, Haute Garonne, France.(Previously: Ellesmere Port, Cheshire, UK.) Posts: 3,184	Re: Suggest a use for this wierd Colvern Pot. Hi, How daft am I? I always thought that the display on a radar display screen was produced by physically rotating the scan coils, fed via slip rings, around the neck of the CRT. Doh! I shall take myself off and stand in the corner. Cheers, Pete. __________________ "Hello?, Yes, I'm on the train, I might lose the signal soon as we're just going into a tunn..."

11th Mar 2020, 12:30 am	#9
MeerKat Hexode Join Date: Jan 2016 Location: Ramsgate, Kent, UK. Posts: 298	Re: Suggest a use for this wierd Colvern Pot. You are not daft Tractorfan, I know some marine radars that do this! Regards, __________________ Andrew Illegitimi non carborundum

11th Mar 2020, 10:06 am	#10
M0FYA Andy Nonode Join Date: May 2007 Location: Preston, Lancashire, UK. Posts: 2,511	Re: Suggest a use for this wierd Colvern Pot. British wartime airborne radars typically used the ubiquitous VCR97, VCR138, VCR139 and VCR517 tubes, all electrostatically scanned. Electromagnetic scanning came in post-war, and yes, one approach was to mechanically rotate the scanning coils. Andy

11th Mar 2020, 12:08 pm	#12
hugozair Triode Join Date: Jan 2010 Location: Penzance, Cornwall, UK. Posts: 34	Re: Suggest a use for this wierd Colvern Pot. And finally...If anyone is ever in need of one of these rare items for a restoration project etc..It's available FOC