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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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Thread Tools |
24th May 2023, 8:51 am | #21 |
Octode
Join Date: Jul 2004
Location: Dundee, UK.
Posts: 1,797
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Re: MoD Voltmeter - wiring arrangement?
Herald1360,
Thank you for pointing out and correcting my serious mistake - a bad slip of the brain. (Shame emoticon x 1000) 6SN7GT, There's a good possibility that the fault with your meter is an open-circuit rectifier, especially if it's copper oxide or selenium. This can fairly easily be replaced, ideally with four germanium diodes, but silicon will probably give sufficient accuracy. You can test the basic meter (without the rectifier) with a variable power supply and a 12k or 15k resistor in series with the movement. Set the supply to around 9V and increase it until you get full scale deflection. PMM |
24th May 2023, 11:19 am | #22 |
Hexode
Join Date: Apr 2021
Location: Crawley, West Sussex, UK.
Posts: 442
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Re: MoD Voltmeter - wiring arrangement?
I often use a DMM set to ohms and manual range where you can therefore 'drive' a movement with a precise and limited current.
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Richard | BVWS & RSGB member | |
24th May 2023, 1:35 pm | #23 |
Heptode
Join Date: Jun 2010
Location: Zurich, Switzerland
Posts: 538
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Re: MoD Voltmeter - wiring arrangement?
Hi Richard,
I do it often too, but these testing currents are, usually ~1mA (not exact=1mA!), so can be too much for some sensitive movement--so: be careful please, begin in higher range! K. |
27th May 2023, 2:12 pm | #24 | |
Hexode
Join Date: Apr 2021
Location: Crawley, West Sussex, UK.
Posts: 442
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Re: MoD Voltmeter - wiring arrangement?
Quote:
But, yes, you do need to be careful - a bit like some older ohm meters and testing 1.4V filament battery valves...
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Richard | BVWS & RSGB member | |
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