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RCA WV-98C: Senior VoltOhmyst refurbished
I picked up this VTVM about a year ago and finally got around to taking a closer look.
The pointer was off a bit so I've removed the button over the meter zeroing control. A little tweaking took care of that. I'll try some Novus on that scratched faceplate. Very solid cast aluminum case. Perhaps an old D cell leaked into that corner ? If it did leak, it couldn't have been too bad. Looks like the previous owner replaced the battery recently. The parts list calls for a selenium rectifier, but that looks like an early silicon one to me. It's all built on a thick PC board. I tested a few of the precision resistors and there all within spec Every capacitor (even the 0.1 uF) is ceramic so I'll leave them alone. I'm going to replace that 10 uF electrolytic, test the D cell and go through the calibration procedure. Last edited by bandersen; 12-08-2010 at 11:53 PM. |
#2
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That's a pretty badass VOM for its time. My boss had one when he first opened his repair shop 38 years ago. He'd still have it if it didn't fall off the bench one day. I might try to find him one someday.
Thanks for bringing this up. Now I gotta look for one.
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Jordan |
#3
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I've had one for years - That and a 90V battery = my capacitor checker. The original probes were gray, then red, and finally a shade of blue. You can't kill the red ones - the gray and blue ones were prone to cracking.
RCA made a whole series of these WV-98's - Junior, Senior and Master VoltOhmysts. Ive got one of each, although the Sr. is my tried and true. Your HP410C is a badass instrument! We used them extensively in the Navy in maintaining old tube-based UHF radios. It was such a comfortable meter to work with that many of the techs could change function and range by feel - only looking up at the meter while for a split second in aligning a radio. Amazing to watch. The techs were more interested in the AF output meter, the Scope, and the RF output meter. 1960's technology, still going strong in the late 80's, and very supportable even then. Cheers,
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Brian USN RET (Avionics / Cal) CET- Consumer Repair and Avionics ('88) "Capacitor Cosmetologist since '79" When fuses go to work, they quit! |
#4
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Very, nice - I think I've only seen a Master once or twice.
My 410C is missing it's AC probe (very hard to find) and the DC volts isn't working properly. The ohms are dead on though so I bet the DC won't be hard to fix. |
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Quote:
As for the DC, always ensure your probe has the requisite 1 Meg resistor in it. It's R1 in the manual. The ohms lead is a straight lead. If the AC probe is missing, a 22 meg resistor, 2 caps (2600pf and 250 pf), and a couple 1N4937's in series (for increased PIV) and you're back in business. Lemme know if you need a 22 Meg resistor - I've got a few Carbon Comp ones, although a 1% 1/2W film type would be best. I built one to try out the concept, but we never used it, as I potted everything and threw off the frequency response at low voltages. Don't pot it and you're okay.... Cheers,
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Brian USN RET (Avionics / Cal) CET- Consumer Repair and Avionics ('88) "Capacitor Cosmetologist since '79" When fuses go to work, they quit! |
Audiokarma |
#6
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Thanks for all the 410C tips I'll take a close look at it once I get this meter all squared away.
Last edited by bandersen; 12-09-2010 at 11:11 PM. |
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One of the very hard to get resistors is off spec :-( It's a 7M 1W 1% that measures 7.35M.
Doesn't seem like much, but it's the first in the range divider network. I put about 136M in parallel to knock it into spec. I had to string together a few 22M and 10M to get the right vallue. I'm still acting strangely though. I can calibrate it on the 50V range so it's dead on at 10V and 50V, but it's off by a tick or so at 20, 30 and 40. A non-lenear response in other words. All the other resistors seem to be within spec and I tried swapping out the tubes. Maybe the meter is off a little ? Not a big deal as it's accurate enough for my needs. I'm just curious what might cause this problem. Perhaps one of the ceramic caps is a little leaky ? |
#8
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The units are rated at 2 or 3% of full scale. That interprets to 4.5 volts off when reading 50 volts on the 150 volt scale. It could read 54.5 volts or 45.5 volts and be in spec.
That is the reason some test procedures call for reading at the upper 1/3 of the lowest possible scale. Meter non-linearity is the biggest problem for mid-scale errors. They were factory calibrated at 48 volts. They were then tested at half scale and full scale on the other ranges. |
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Thanks for the info. Seems my meter is well within spec.
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#10
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Just looked at mine and there should be a selenium rectifier in there. Now if a diode has been used there should be a resistor in series with it to equal the voltage drop of the selenium.
__________________
Main system Scott LK-72A amp & LT-110 tuner Garrard Zero 100C turntable AKAI GX 255 RTR iPod & computer DIY speakers (upgrading them soon) |
Audiokarma |
#11
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It sure looks like it's the original and it's silicon. Perhaps this is a later revision ?
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#12
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Could be.
__________________
Main system Scott LK-72A amp & LT-110 tuner Garrard Zero 100C turntable AKAI GX 255 RTR iPod & computer DIY speakers (upgrading them soon) |
#13
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I have a manual (paper copy) for one of these...yet, I dont have one. You are welcome to it, if you need it. Has instructions, adjustments, schematic, etc. PM me and I'll gladly send it to you...
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#14
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Thanks for the offer but I've got a copy. Maybe someone else could use it ?
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#15
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What probe is that on the front cover of the manual? Mind didn't come with a probe.
__________________
Main system Scott LK-72A amp & LT-110 tuner Garrard Zero 100C turntable AKAI GX 255 RTR iPod & computer DIY speakers (upgrading them soon) |
Audiokarma |
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