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Old 01-16-2018, 10:39 AM
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AlanInSitges AlanInSitges is offline
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Q: How long does the D battery in an RCA Senior VoltOhmyst WV-98C last?

A: A really freaking long time!







I've started to put together a bench 25 years after I lost all my TVs, test equipment, and stock of replacement parts. My first purchase was this sweet RCA VTVM, from a guy in Italy on eBay. It's a 220V European model (who knew?)

Opening up the case I was quite surprised to see the original RCA-branded dry cell still soldered in place, and showing almost full voltage!

I've since cleaned the meter up, replaced a rotted power cord, and tested the probe to find it showing infinite resistance. I managed to get it apart, but just the cable shows a resistance between 0 and 5 ohms that varies when you move it around - it's also not very flexible anymore.

The sensible thing seems to be to replace the entire probe and cable assembly. I've seen new "replacements" on eBay but they are just cheap VOM-type probes. Anyone have a suggestion for something that's a little more like the original? And maybe incorporates the AC/DC switch? I'd be willing to get rid of the UHF connector and replace it with a BNC too, I suppose.
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Old 01-16-2018, 01:18 PM
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Electronic M Electronic M is offline
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The cable is probably common 50 OHM instrumentation coax. If you can get the probe apart and back together, then you can rebuild the probe. Change the coax, and any fixed resistors, capacitors, diodes in it as well as clean and test the switch. it should be good as new then. (original body circuit and plugs, but with better perishable components)

That connector is actually a Mic connector...UHF connectors have a thick center pin/receptacle, instead of the two blobs of solder that Mic connectors smush together...I believe those Mic connectors are also older. I've seen Mic connectors on 30's gear, but I can't recall seeing any UHF connectors on pre-WWII equipment.

It is fine to keep the mic connectors if you feel like it...Most are made to be easily swapped between different coax with a soldering iron....If you fail putting the plug on the new cable just goto BNC.
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Old 01-16-2018, 08:32 PM
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init4fun init4fun is offline
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That 10 MFD electrolytic near the battery would be on my short list of things to replace if that were my piece of test equipment .
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Old 01-17-2018, 10:23 AM
dieseljeep dieseljeep is offline
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Quote:
Originally Posted by Electronic M View Post
The cable is probably common 50 OHM instrumentation coax. If you can get the probe apart and back together, then you can rebuild the probe. Change the coax, and any fixed resistors, capacitors, diodes in it as well as clean and test the switch. it should be good as new then. (original body circuit and plugs, but with better perishable components)

That connector is actually a Mic connector...UHF connectors have a thick center pin/receptacle, instead of the two blobs of solder that Mic connectors smush together...I believe those Mic connectors are also older. I've seen Mic connectors on 30's gear, but I can't recall seeing any UHF connectors on pre-WWII equipment.

It is fine to keep the mic connectors if you feel like it...Most are made to be easily swapped between different coax with a soldering iron....If you fail putting the plug on the new cable just goto BNC.
VTVM probes have only one component besides the switch, a 10 megohm resistor.
Those mic connectors are easy to remove and install on the new cable, usually RG58U. That co-ax was common on CB antennas.
The dry-cell was used only on high ohms, so the life was generally shelf-life.
The Knight-kit VTVM I built in 1962 had a Ray-O-Vac "C" cell that still checked good 30 years later, but I replaced it anyway. Still have the meter.
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Old 01-17-2018, 03:29 PM
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jr_tech jr_tech is offline
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Quote:
Originally Posted by dieseljeep View Post
The Knight-kit VTVM I built in 1962 had a Ray-O-Vac "C" cell that still checked good 30 years later, but I replaced it anyway. Still have the meter.
My 1958 Heathkit V7a Ray-O-Vac "C" cell was measured today at 1.35 volts and it is still leak proof!

Not bad for nearly 60 years!

jr
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Old 01-18-2018, 11:44 AM
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AlanInSitges AlanInSitges is offline
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Thanks everyone for the input. That probe isn't going back together; evidently they weren't designed to be disassembled and the switch isn't really a switch, just a few pieces under pressure that short out the resistor when it's activated. It only has a 1M resistor in it. I think I'll just buy some of the cheap ones from eBay and be done with it.

The electrolytic is already replaced.
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Old 01-18-2018, 03:19 PM
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I understand the Mercury-type battery was specified by RCA for a more precise voltage over its shelf life.
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