Simpson 312 VTVM

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Simpson 312 VTVM

Post by the.doc on Sun Sep 10, 2017 2:50 am

I just got an old Simpson 312 VTVM and downloaded a copy of the manual. In the manual is a parts list, and two of the capacitors are listed as "paper". One is a CDE Black Cat and is all sealed up in plastic and looks brand new. The other one in not CDE and is much smaller, but looks just as good. (The inside of this meter is really clean.)

When I saw "paper" in the parts list, I expected to see wax oozing out of them once I got in open, but they look brand new. I don't know what's inside these caps, and I can't find any descriptions of that on the web, so I'm turning to you guys for help.

I will change out the electrolytic before turning it on, and I'm leaning toward replacing the probe connector with BNC.

Any comments gladly received. Here's a screenshot of the manual listing for these caps.

thanks



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Re: Simpson 312 VTVM

Post by Chas on Sun Sep 10, 2017 10:50 am

C-D black cats are an oiled paper/foil construction. The ARE leaking (electrically), sometimes the oil too, (mineral). Replace with foil/film cap rather than a metalized, resistance to dv/dt is needed in this application.

I had a 2000pc. lot of C-D Black Cat caps all through the mf range to 2mf. Everyone leaked, some so badly the bridge would not balance... I had hoped to pass them along as "tone" caps but they were not even good for that...

Best advice is not to replace the connector to avoid using generic test leads of incorrect voltage tolerance. Should the desire to use a multiplier resistor for HV (probe) the BNC would make it impractical to manage the HV wire.

The use of an RF detector probe would be inhibited too.

All but one of my instruments has the original connectors. The GR 1001a was converted to UHF, before I got it...

YMMV

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Re: Simpson 312 VTVM

Post by the.doc on Sun Sep 10, 2017 9:56 pm

Chas said:
Replace with foil/film cap rather than a metalized,

If somebody would make a concrete suggestion here, I'd really appreciate it. I tried looking around on the web and just got bewildered.

.068 uf at 1000 volts foil/film
.02 uf at 400 volts foil/film


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