Hand wound Evershed & Vignoles 'megger' hair spring question - Page 2 - UK Vintage Radio Repair and Restoration Discussion Forum

The Philpott · 27th Jan 2018, 12:05 pm

You take it on 'cos there's nothing to lose..!? The other reason i cite personally, is if i've done a stint on micro mechanics, it's a relief and less of a challenge to confront the guts of something big, bold and brassy like a Badische wall clock. It's nice to know the old wee megger is still economical to buy.. and often fully functional.

Phil G4SPZ · 27th Jan 2018, 12:35 pm

Yep, good point. I don't collect stuff unless it works, or can be made to work!

The Record Bond Tester is a 4-terminal battery-powered milliohmmeter dating from the WWII era and used, I believe, for earth bonding measurements on military aircraft. It was powered by a 1.2 volt wet Nickel-Iron alkaline accumulator and injects a test current of some 2 amps into the resistance under test. The instrument measures the small voltage appearing across the resistance. Current and voltage are applied to the now-familiar twin-coil movement, resulting in a deflection proportional to resistance. The scale range is 0.0 ohms to 0.1 ohms FSD. Judging from the serial numbers, at least 6,000 were made.

I want to use it for measuring the low resistance shunts used in Avometers and similar ammeters. I bought two of these in scrap condition at the NVCF a few years ago, hoping to make one good working example out of the two. One has a smashed Bakelite case, and both had suffered severe internal corrosion from leaking accumulator electrolyte. I suspect that fate befell the majority of these meters, so they're relatively scarce now and I can find nothing at all about them on the web. The legend "A.P. 19744" which is an Air Ministry "Air Publication" reference number appears on the scale plate, and when time permits I'll do a bit more research.

Phil

Sinewave · 27th Jan 2018, 4:49 pm

I've got one of these which only outputs 80 volts. Might get round to resoring it some day.

Phil G4SPZ · 5th Feb 2018, 9:04 am

Quote:

Originally Posted by Phil G4SPZ

...I have a Record bond tester with a similar movement that has been corroded by battery leakage. The ligaments look impossible to repair...

Well, I'm delighted to report that I have proved myself wrong! The movement is now fixed. Thanks to Sam

for the suggestion of using an aggressive flux, which after a few false starts was ultimately successful.

Watch out for a Success Story in due course

Boater Sam · 5th Feb 2018, 9:15 am

I don't believe it!
I got something right for a change.
Did you manage to wash all the flux off Phil? It may go green otherwise. I don't know what would neutralise it safely, acid or alkali.
Pleased that you had another success despite the microsurgery, well done.

Phil G4SPZ · 5th Feb 2018, 10:04 am

Thanks, Sam. Mmm... getting all the flux residue off was nigh-on impossible. These ligaments are so light they wave about like confetti in the slightest breeze, so holding them still is a challenge. I actually used a flux which is alleged to be non-corrosive.

Fingers crossed the repair will last a while.

27th Jan 2018, 12:05 pm	#21
The Philpott Dekatron Join Date: Aug 2016 Location: Colchester, Essex, UK. Posts: 4,107	Re: Hand wound Evershed & Vignoles 'megger' hair spring question You take it on 'cos there's nothing to lose..!? The other reason i cite personally, is if i've done a stint on micro mechanics, it's a relief and less of a challenge to confront the guts of something big, bold and brassy like a Badische wall clock. It's nice to know the old wee megger is still economical to buy.. and often fully functional.

27th Jan 2018, 12:35 pm	#22
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: Hand wound Evershed & Vignoles 'megger' hair spring question Yep, good point. I don't collect stuff unless it works, or can be made to work! The Record Bond Tester is a 4-terminal battery-powered milliohmmeter dating from the WWII era and used, I believe, for earth bonding measurements on military aircraft. It was powered by a 1.2 volt wet Nickel-Iron alkaline accumulator and injects a test current of some 2 amps into the resistance under test. The instrument measures the small voltage appearing across the resistance. Current and voltage are applied to the now-familiar twin-coil movement, resulting in a deflection proportional to resistance. The scale range is 0.0 ohms to 0.1 ohms FSD. Judging from the serial numbers, at least 6,000 were made. I want to use it for measuring the low resistance shunts used in Avometers and similar ammeters. I bought two of these in scrap condition at the NVCF a few years ago, hoping to make one good working example out of the two. One has a smashed Bakelite case, and both had suffered severe internal corrosion from leaking accumulator electrolyte. I suspect that fate befell the majority of these meters, so they're relatively scarce now and I can find nothing at all about them on the web. The legend "A.P. 19744" which is an Air Ministry "Air Publication" reference number appears on the scale plate, and when time permits I'll do a bit more research. Phil Attached Thumbnails __________________ Phil Optimist [n]: One who is not in possession of the full facts Last edited by Phil G4SPZ; 27th Jan 2018 at 12:37 pm. Reason: Clarity

27th Jan 2018, 4:49 pm	#23
Sinewave Octode Join Date: May 2016 Location: Oxfordshire/Bucks borders, UK. Posts: 1,604	Re: Hand wound Evershed & Vignoles 'megger' hair spring question I've got one of these which only outputs 80 volts. Might get round to resoring it some day. __________________ Avometer, vintage Fluke and Marconi collector. Also interested in vintage Yaesu and KW.

5th Feb 2018, 9:15 am	#25
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Hand wound Evershed & Vignoles 'megger' hair spring question I don't believe it! I got something right for a change. Did you manage to wash all the flux off Phil? It may go green otherwise. I don't know what would neutralise it safely, acid or alkali. Pleased that you had another success despite the microsurgery, well done.

5th Feb 2018, 10:04 am	#26
Phil G4SPZ Dekatron Join Date: Apr 2005 Location: Bewdley, Worcestershire, UK. Posts: 4,748	Re: Hand wound Evershed & Vignoles 'megger' hair spring question Thanks, Sam. Mmm... getting all the flux residue off was nigh-on impossible. These ligaments are so light they wave about like confetti in the slightest breeze, so holding them still is a challenge. I actually used a flux which is alleged to be non-corrosive. Fingers crossed the repair will last a while. __________________ Phil Optimist [n]: One who is not in possession of the full facts