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Very vintage Precision apparatus vtvm model ev10

Carbsandcaps

Carbsandcaps

Super Member
Check out this vtvm I just picked up. In it original wooden case AND with its original probes! It’s like a work of art. Not very useful today but certainly a conversation piece. It turns on but I can’t get the needle to move trying to check ohms. I should probably find a manual or video on it since I don’t know what does what but I can’t wait to get it rebuilt and running assuming the meter isn’t blown. Looks like it took a battery or was retrofitted at some point as well. Anyone have any info on these?
 

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Nice! There is a ton of stuff that I work on where that meter would get me by just fine, even by todays standards. Seems to have some interesting ranges too :)
 
Interesting, you don't see many VTVMs with a VR tube. About the ohmmeter, every VTVM I've ever seen uses a battery to measure resistance. Battery eliminators were sold for some of the later models.

Jack
 
Actually, tube voltmeters can come in very handy when testing certain other devices. Digital meters can crap out or give you false readings in a lot of situations. Hope you can get it up and running.
 
TriodeLuvr said:
Interesting, you don't see many VTVMs with a VR tube. About the ohmmeter, every VTVM I've ever seen uses a battery to measure resistance. Battery eliminators were sold for some of the later models.

Jack
Click to expand...
Yes you’re right! If forgot about that I have a heathkit vtvm that I made a makeshift power supply to replace the 1.5v battery. I’ll have to see if I can figure out what voltage this one requires.
 
The link below is a discussion regarding the EV-10A. There's a schematic for an EV-10S, which might be similar to the EV-10A and maybe also the EV-10. I also see mention of batteries for the resistance ranges, and a link to an EV-10S restoration page. Good luck with it!

Precision EV-10A Discussion

Jack
 
Sometimes the battery is for bias on the amplifier tube. Lots of them seem to use a 1.5v cell of some form for that.

My RCA had been previously modified to have a single diode and a cap off the 6.3 vac supply into a resistor and a chain of 3 common diodes to serve as a zener to lock it to about 1.5v for that purpose. Looks messy, works fine.
 
Well I got the few capacitors it has replaced. Found the ground wire at the vtvm probe broken off so fixed that but whenever I plug in the probe the pilot light gets very dim. It looks like the 6.3v filament voltage goes to the ground on the probe which makes no sense to me but the negative side of the probe is shorting to ground when I install it.
I did use a multimeter in the meter and it has continuity and actually moved when I tested it using my ohmeter.
 

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Interesting that the filament winding for the 6X5 is labeled "5-VOLTS." Must be a typo.

Jac
 
Ok I got it working. The probe was all kinds of assembled wrong so I disassembled, cut some clean wiring and required it correctly. Then I found a video on how it works and found that it will actually read without power so I tested a battery and it worked. The meter is supposed to move to center when powered up but it wouldn’t move. I had 9 volts at the meter on both sides. I disconnected the negative side and had no voltage on the negative side. Tracing the power supply I found an open 8500 ohm resistor. I quickly threw together a 1000 and 7500 ohm resistor. Boom the meter came to life! I’ll check some other things tomorrow. IMG_4393.jpegIMG_4394.jpegIMG_4395.jpeg
 
The zero points are adjustable on these, the center zero thing can be used for basic FM alignments. The detector is typically set to 0 volts
 
gadget73 said:
The zero points are adjustable on these, the center zero thing can be used for basic FM alignments. The detector is typically set to 0 volts
Click to expand...

There’s a bunch of pots that are “sealed and calibrated” I’m guessing that’s where they come in. There’s zeroing dials on the front but the ohm zero dial seems to be maxed out.
 
arts said:
For non-critical areas like the zero-adjust controls they used regular carbon composition resistors. They've probably drifted pretty far off tolerance by now.
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That’s a good point. There are some cheap brown resistors and some that are precision resistor brand. Those are still within 1% after 50 plus years pretty impressive. I haven’t measured the cheap ones yet
 
The precision ones are generally in the voltage range selector. Those need to be accurate long term. Quite probably wirewound, those don't really have drift problems and it would have been the more common way to create a precise, stable resistor long ago.
 
After a close look at the schematic I found that this actually uses a 6v battery (4 D cells) instead of the normal 1.5v. That made my life a whole lot easier since I had a 6v switching power supply laying around. Wired into the power switch and it puts out 6.04v even under ohm zero test which is full short it holds its voltage. Its seems to be pretty accurate too with a 1000ohm resistor. Voltage readings are perfect too.

I cleaned the face with spray nine and guess what? It’s actually white! I thought this was a different version than the others I’ve seen online. Nope just years of cigarettes. I kind of like the off white better but oh well. I think I’ll leave it just the way it is for now
IMG_4399.jpegIMG_4401.jpegIMG_4403.jpegIMG_4406.jpeg
 
Here’s a website of how to use it for anyone who comes across this thread. The video shows it in action but doesn’t give any explanations so I had to freeze the video and zoom in on what connections he was using. Mine has a different layout but similar connections.
lazyelectrons.wordpress.com

Precision Apparatus EV-10A – Multi tester & VTVM – Restore / Repair

This is another strange looking instrument from 1950s era. Took me a while to understand what it is really, so here is the summary – It is a VTVM + Normal Volt Meter. Which means it can ope…
lazyelectrons.wordpress.com lazyelectrons.wordpress.com
 
Carbsandcaps said:
Nope just years of cigarettes. I kind of like the off white better but oh well. I think I’ll leave it just the way it is for now
Click to expand...
I haven't smoked in a long time, but if you want you can send it up here and I'll throw it in the case with my bass for a couple of weeks. She'll be back lookin' and smellin' like an ashtray in no time :thumbsup:
 
I spend too much time working on stuff at a very old Elks lodge. Smoking in the building ended around 2006 I think. I was working on the fluorescent lights the other day and they still had the smell. Those lights I'd wager have been in place since at least the 1970s.
 
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