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Vintage Test Gear and Workshop Equipment For discussions about vintage test gear and workshop equipment such as coil winders.

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Old 16th Apr 2017, 9:42 am   #1
Gridiron
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Default Early Evershed Ohmmeter

This came from the BVWS stall at Golborne, I believe it is the earliest version of the Evershed Ohmmeter (forerunner of the Megger). According to the article in the BVWS Bulletin for Spring 2014 by the late J. Patrick Wilson it was made between 1889 and 1895, when replaced by a new version with levelling screws and a rectangular window for the movement.
The movement coils appear to have been rewound (one is open circuit) as they have Paxolin end washers, I don't think this material would have been available in the 1890's. The separate generator unit was not with the meter, unsurprisingly.
Mike.
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Old 16th Apr 2017, 12:45 pm   #2
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Default Re: Early Evershed Ohmmeter

I have got a big heavy one and I still use it. Mine was also missing the external generator. That did not stop me making one though.
http://golbornevintageradio.co.uk/fo...ghlight=megger
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Old 16th Apr 2017, 9:18 pm   #3
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Default Re: Early Evershed Ohmmeter

The dating seems correct: it looks identical with the one shown in GEC's 1893 catalogue: scan attached, which includes instructions for use. Designed for a 100V to 120V magneto, no doubt reflecting the contemporaneous mains supply voltages: nothing for supplies greater than 120V in the 1893 catalogue. Available to hire at 2/6d per day if you could not afford £18/10/- to buy one.
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Old 16th Apr 2017, 9:39 pm   #4
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Default Re: Early Evershed Ohmmeter

That's interesting as the generator voltage on the instructions in the lid has been altered from 100 volts to 200 volts (inked over), presumably for use with a later generator when regulations became more stringent and testing had to be done at higher voltage. Possibly the coils were rewound for use with the later generator?
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Old 16th Apr 2017, 10:17 pm   #5
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Default Re: Early Evershed Ohmmeter

Only Meggers with built-in generators are shown in the 1911-12 GEC catalogue: 10 different models, covering operating voltages between 100V and 1000V, two different resistance ranges, and either constant voltage (using a slipping clutch), or voltage proportional to crank rotation (to provide over-voltage testing). Daily hire was still available, but now the first 2 days cost 5/- per day, with 2/6d per day for each subsequent day. They also did a couple of "Bridge Megger" test sets that incorporated a Wheatstone bridge and had to be used with a separate resistance box, allowing resistances of as low as one Ohm to be measured..
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