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.
http://farm6.static.flickr.com/5210/5245347459_2026db6f3c_b.jpg

Very solid cast aluminum case. Perhaps an old D cell leaked into that corner ?
http://farm6.static.flickr.com/5204/5245347623_e066e66b2c_z.jpg

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.
http://farm6.static.flickr.com/5208/5245947744_1095ec6717_z.jpg

It's all built on a thick PC board.
http://farm6.static.flickr.com/5121/5245348267_6d07e73777_z.jpg

I tested a few of the precision resistors and there all within spec :thmbsp:
Every capacitor (even the 0.1 uF) is ceramic so I'll leave them alone.
http://farm6.static.flickr.com/5285/5245348515_41f2c6fac0_z.jpg

I'm going to replace that 10 uF electrolytic, test the D cell and go through the calibration procedure.

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.

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,

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.

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.

The 410C manual is everywhere - and free - Agilent and BAMA both have them.

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,

Thanks for all the 410C tips :thmbsp: I'll take a close look at it once I get this meter all squared away.

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.
http://farm6.static.flickr.com/5050/5250560730_84f2ae79b6_z.jpg


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 ?

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.

Thanks for the info. Seems my meter is well within spec.

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.

It sure looks like it's the original and it's silicon. Perhaps this is a later revision ?

Could be.

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...

Thanks for the offer but I've got a copy. Maybe someone else could use it ?

What probe is that on the front cover of the manual? Mind didn't come with a probe.

I have a 2 manuals for RCA Senior Voltohmsyts - one is for WV-98C and one is for a WV-98A. They came with some other older equipment I bought, but these items weren't there, just these manuals.
So I don't need them - if someone else does, just let me know.

What probe is that on the front cover of the manual? Mind didn't come with a probe.

It's a WG-299 type probe like this: http://www.radiomuseum.org/r/rca_voltohmyst_probe_wg_299d.html

It has a mode switch for DC / AC, Ohms. The switch puts a 1M resistor in series with the tip.

Oh ok. So that is why the meter seemed off on DC voltages. Looks like I may just make a box with the switch and resistor. I would then use shielded cable to go from the connector to maybe a BNC connector on the box then have the switch and resistor along with two banana jacks so that I can use regular meter leads.

Hi:

I have fully restored my RCA SENIOR VOLTOHMYST WV-98C. It had a few out of tolerance precision resistors.

Thanks to banderson's tip to use a parallel resistance calculator from the internet I was able to adjust these back to within 1% tolerance.

The problem I have now is the 1Meg ohm resistor in the WG-299D probe is out of tolerance. I have no idea how to disassemble this. I twisted it like crazy. Any harder I think it would break!

The other thought is this. Since it is about 10% out, does it really matter anyways when I come to the point of calibrating the meter? In other words would calibration overcome this out of tolerance value?

Any experience? Any ideas?

Thanks

I assume that those precision resistors are not available new? I may check mine and start replacing resistors. Concerning the resistor in the probe could you just make a new probe with a new resistor? Unfortunately mine has no probe so I would have to make one.

Generally they're not available new or if they are, they're very expensive. Surplus Sales of Nebraska has some at reasonable prices though.

True I didn't think about that.

1 meg precision resistors are EASY to find new, and are inexpensive up to about a watt. I recently got some 10Meg 1 Watt bleeder resistors for under a buck each. Mouser, Allied, Digi-Key, and Newark all have them, as do several surplus vendors as Bob mentioned. Talon has them from 1/8 Watt to 1 Watt, all under a buck each:

http://www.talonix.com/shop/category.aspx?catid=96&page=4&sortby=

Cheers,

Mouser has just about any resistor you could want or need. I only have had maybe one case where they did not have one resistor I needed and I sometimes need some weird values.

Mouser has just about any resistor you could want or need. I only have had maybe one case where they did not have one resistor I needed and I sometimes need some weird values.

Quite true, but their price breaks come at 25 or 50 quantity. I needed 7 10Meg 1 watt metal film resistors, so buying 10 for less than they cost at Mouser was a plus. ( 6 bucks vs 13) Same with Electrolytics - I can sometimes buy 10 or more for the cost of 5 or 6 at Mouser. I use Mouser sparingly, as Allied and Digi-Key often have stuff for less. I just wish everyone had a parametric, drill-down search like Mouser has. Now that they've added Panasonic caps, I get my film caps from Mouser or Digi-Key, which has distributed Panasonic since 1977. Quality mylar/polypropylene/polyester caps, shipped from the USA, for pennies each? I'm happy.

Cheers,

Hmm. I like Mouser and use them all the time but couldn't find any 7M resistors. The closest are 6.98M or 7.15M and neither at 1 W :( I guess I'll try Surplus Sales of Nebraska next time I need enough to build up a full order.

A friend had two of them beqethed to him and one had a stuck needle so he offered it to me. I admittedly know little of electronics, but mechanics I like, so I took it apart right away.
The probe attaches right in the middle of the coil that operates the needle, and with a minor adjustment (a couple screws) it bounces about as nice as if new (I can only imagine, since I was probably born when this thing was)!

Anyhow, now I have the bug to use it - is this a nice tool to welcome me into electronics?

And geartech - do you still have an extra copy of the manual for this? Anyone have a digital copy?