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Registered Member #396
Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176
Hi there,
I picked up an expanded scale 120VAC meter made by Simpson, probably circa 1960. Unfortunately I can only get it to deflect when I apply >120V, even though it measures from 100-130V.
Has anyone ever seen one of these before? It looks like it was hand assembled and its very difficult to see whats going on in it because of the cramped wiring.
Registered Member #230
Joined: Tue Feb 21 2006, 08:01PM
Location: Gracefield lower Hutt
Posts: 284
The black disc is probably a varistor of value 100 volts. you can approximate these with a new varistor or a bidirectional 90volt protection diode it has to be bidirectional to make the moving iron meter work
Registered Member #396
Joined: Wed Apr 19 2006, 12:55AM
Location: Pittsburgh, PA
Posts: 176
johnf wrote ...
The black disc is probably a varistor of value 100 volts. you can approximate these with a new varistor or a bidirectional 90volt protection diode it has to be bidirectional to make the moving iron meter work
Thank you. After some testing it does seem to be a 4.4v varistor. The low value is because the unit contains a step down transformer so all circuitry after that is at low potential.
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Expanded scale voltmeter
