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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Aug Fri 14, 2020 12:11 am 
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yea, that's a ridiculous price unless it's "museum quality" whatever that means. And even then, it's still a ridiculous price. I've picked them up for $15 at estate sales or auctions. Some day I should probably restore a few of them. And sell them for $300. :-D

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Aug Fri 14, 2020 1:30 am 
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stevebyan wrote:
ttx450cap wrote:
are you the guy that paid almost $300 on ebay for that the other day.

No. $300 for a non-restored RCA WV-98C? Sounds like some shill bidding to me, no sane person would spent that for an unrestored WV-98, and even a restored one is unlikely to sell for that high a price. Unless it's in the original box or something.

Edit: I found the auction. It is one of the cleaner WV-98C's I've seen, especially for being from one of the earlier runs (old-style paint scheme, logo, and knobs). And an intact WG-299D probe is worth a bit by itself. Also it is guaranteed to be "working". I doubt it's been recently calibrated, though.


not sure you can see this.. looks like it works

https://www.ebay.com/itm/RCA-WV-98C-Sen ... _cvip=true

https://www.ebay.com/bfl/viewbids/12428 ... 7675.l2565

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Aug Fri 14, 2020 1:32 am 
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I bet it goes back up for auction after the non paying bidder backs out.


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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Aug Fri 14, 2020 1:33 am 
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Barry H Bennett wrote:
yea, that's a ridiculous price unless it's "museum quality" whatever that means. And even then, it's still a ridiculous price. I've picked them up for $15 at estate sales or auctions. Some day I should probably restore a few of them. And sell them for $300. :-D


ebay is going scary crazy.. everyone driving the prices up. people that dont know, just search prices on ebay and believe thats what it is worth. up and up and up

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Aug Fri 14, 2020 1:34 am 
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fordtech wrote:
I bet it goes back up for auction after the non paying bidder backs out.


I swear I see people buying some of this stuff and then put it back up with some ridicules price..

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Aug Fri 14, 2020 1:36 am 
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Barry H Bennett wrote:
yea, that's a ridiculous price unless it's "museum quality" whatever that means. And even then, it's still a ridiculous price. I've picked them up for $15 at estate sales or auctions. Some day I should probably restore a few of them. And sell them for $300. :-D


I'll take a calibrated unit for $50 :mrgreen:

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Aug Fri 14, 2020 2:08 am 
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Quote:
I'll take a calibrated unit for $50 :mrgreen:

nonononono....you have to take ALL of them. 8)

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Aug Sat 15, 2020 4:47 pm 
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Barry H Bennett wrote:
Quote:
I'll take a calibrated unit for $50 :mrgreen:

nonononono....you have to take ALL of them. 8)


:cry:

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Sep Wed 02, 2020 5:11 pm 
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Update #4

I decided to complete the run L60 unit first.

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I started by reconnecting the front panel Zero and Ohms controls. I made good use of the photos I had taken during disassembly. The photos combined with RCA’s use of color-coded wires made the job pretty easy.

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The next step was to reinstall and reconnect the Amphenol 75-PC1M chassis connector for the probe, and re-mount the lower support bracket. The kit instructions were somewhat helpful, although I was doing some steps out of sequence.

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I still have to construct and install a battery eliminator for the ohmmeter circuit. Unlike the Heathkit VTVMs, the RCA WV-98’s use a floating battery. Neither side of the battery is connected to the chassis.

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My design for the Heathkit IM-13 battery eliminator assumes the negative end of the battery is grounded to the chassis, and the PC layout achieves this through one of the mounting stand-offs. I’ll either have to design a new PCB for the RCA WV-98’s or hack up a mounting method that leaves the negative rail of the supply ungrounded.

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It looks like a VTVM again! And an initial checkout and preliminary calibration shows it to be working, with the exception of the ohmmeter portion due to the lack of a power supply.

One common issue with VTVMs is that the 12AU7A initially has a high grid current. This shows up as the zero drifting up as you switch to the lower voltage ranges. When I first turned it on, when I zeroed the meter on the 50 volt DC range, the needle would drift up to the “5” mark on the 0-50 DC scale when I switched to the 1.5 volt range. That’s about 10% of full scale.

The high grid current is due to gas in the tube, leaking in over all the years it sat abandoned and not in use. After leaving the VTVM powered-on for three days, the getter scavenged much of the gas from the tube and the zero drift on the 1.5 volt range went down to about 1/2 of a division on the 0-50 DC scale, which is about 1% of full scale.

Note that the zero drift is much larger on the 0.5 Volt DC range. The RCA manual instructs you to re-zero the meter when switching to the 0.5 V DC range.

Now that it has aged a bit, I can start to do the final recalibration. I’ll ponder the battery eliminator question for a while, and leave deciding on an approach until after I’ve reassembled the other two meters.

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Last edited by stevebyan on Sep Tue 08, 2020 2:51 pm, edited 1 time in total.

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Sep Sat 05, 2020 4:46 am 
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Update #5

I’ve completed calibrating the run L60 unit, except for the resistance ranges.

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Click the above thumbnail for a readable image. The VTVM easily beats its accuracy specification.

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 Post subject: Re: Restoring an RCA WV-98C
PostPosted: Sep Sat 05, 2020 12:52 pm 
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stevebyan wrote:
Image
Does anyone know who made these precision resistors? I don’t recognize the logo, nor the initials "RC".

Hi Steve,

Those are Rosenthal resistors, now part of Vishay?
https://www.vishay.com/landingpage/50year/
Those resistors are from the '50s and '60s.
That web-page should give some answers, perhaps, but it did not load on my browser!

Really nice and thorough restoration, kudos to you!

Regards, Peter


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 Post subject: Re: Restoring an RCA WV-98C
PostPosted: Sep Sat 05, 2020 2:52 pm 
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orbanp wrote:
Those are Rosenthal resistors, now part of Vishay?
https://www.vishay.com/landingpage/50year/
Those resistors are from the '50s and '60s.
That web-page should give some answers, perhaps, but it did not load on my browser!

Thank you for that information.

I had to install Flash to view the history presentation. Unfortunately I could not find there any reference to Rosenthal. I'll have to look through some old Radio Electronic Masters to see if I can dig up some information on Rosenthal.

orbanp wrote:
Really nice and thorough restoration, kudos to you!

Thank you Peter.

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Sep Sat 05, 2020 5:42 pm 
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Hi Steve,

Here are references to Rosenthal resistor production:
https://www.vishay.com/landingpage/50year/draloric.html

Regards, Peter


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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Sep Sat 05, 2020 7:41 pm 
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Thanks Peter! Interesting history there.

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Sep Tue 08, 2020 10:53 am 
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Hi folks,

Very interesting thread thanks. I picked up a WV-98C recently and found the power transformer has overheated in a previous life. The primary and heater windings seems OK but the HT winding is only producing about 75V and the TX runs hot even with both secondaries unloaded. My guess is that the 10uF capacitor went bad and overloaded the HT winding.

I've tried to find a replacement TX but no luck and I don't want to buy another meter just to harvest the transformer. Any suggestions for a source for this item would be greatly appreciated.

thanks,

Pete.


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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Sep Tue 08, 2020 2:49 pm 
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Pete67 wrote:
Any suggestions for a source for this item would be greatly appreciated.

Earlier in this thread, rja2907@comcast.net (Jim) posted that he had two WV-98's with bad meters:
viewtopic.php?p=3219306#p3219306

He offered parts from them to anyone needing WV-98 parts.

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Sep Tue 08, 2020 3:01 pm 
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I happen to know that Bob (gcvm on ARF) has several of these and may be able to help you with parts.

You can email him from his profile page:

https://antiqueradios.com/forums/memberlist.php?mode=viewprofile&u=42516

Tell him Chuck sent you!

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Last edited by WoodchuckTN on Sep Wed 09, 2020 2:06 am, edited 1 time in total.

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Sep Wed 09, 2020 12:10 am 
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looks nice.. want to get one, one of these days.

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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Sep Wed 09, 2020 1:21 am 
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Wish this thread was available when I restored my 98c.

My restoration was no where near as comprehensive as yours, and its a good thing because my meter is working fine without full disassembly - which in my case - might not have gone so well at reassembly - lol.

Nice work!


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 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Tue 13, 2020 2:07 pm 
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Thanks, Codepug!

Update #6

I’ve completed the run K114 and run K117 units, except for calibration, and added battery eliminators to all of the VTVMs.

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Here’s the run K114 unit with the range and function switches re-installed on the PCB.

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Reconnecting everything was a bit tedious.

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Here is the run K117 unit.

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On the run K114 unit, I lost the Heyco clip for the line cord. I tried all the different sizes of the Philmore brand Heyco clips carried by my local electronics parts emporium, Electronics Plus, but none of them would fit.

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I cons’d up a replacement using a cut-down Waldom vinyl grommet ...

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… and an Underwriter’s knot for strain-relief on the line cord.

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I also made up a home-brew replacement for the original RCA WG-299D probe for the run K117 unit. I prefer to keep the original Amphenol 75-MC1 connectors, rather than replacing them with BNCs.

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Here I’ve mounted my transformer-powered VTVM battery eliminator circuit in the run K117 unit.

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I mounted it using #6 x 3/8 round-head nylon screws and nuts. I used nylon because the board was laid-out assuming the ground bus would be grounded to the chassis through one of the mounting standoffs. However, the WV-98A/B/C VTVMs require a floating voltage source for the resistance range, so I have to isolate the PCB from the chassis ground.

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I used a stack of two #6 nylon washers as spacers to raise the PCB above the chassis. Note the chassis mounting hole next to the left-hand diode. With the board oriented this way, it’s hard to get a screwdriver on the bolt that goes in that hole.

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There’s no pad on the PCB for the negative connection, so I just soldered a wire to the ground bus on the back of the PCB.

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I drilled a hole in the PCB to feed the line voltage to the board. I made the connections to the traces that provide power to the neon pilot lamp.

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On the run K114 unit, I mounted the board rotated 180° compared to the other unit, and put the nuts on the bottom rather than the top.

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This made it much easier to access the chassis mounting screw, here shown in the upper left of the photo.

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Here’s the almost-finished run K117 unit. I burned-in the VTVMs, waiting for the grid current in the 12AU7A’s to drop. The run K114 unit settled in after a couple of days, but even after four days the run K117 unit still had four divisions of grid current on the 0-50 scale when switched to the 1.5 Volt range. It needs a new 12AU7A before I can calibrate it.

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Note that the run K117 unit has a replacement meter and front panel from a later run, with the blue paint rather than the gray hammertone.

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I guess that the old meter was damaged by battery leakage. You can see where the battery leakage damaged the paint on the case at the lower left corner in the photo above.

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The previous owner (MIT’s student EE lab) has touched up the paint on the rear of the case, presumably where the battery leakage damaged it.

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Here’s the complete package.

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Here is the run K114 unit. Note the older style for the front panel legends, compared to the run K117 unit with the replacement new-style front panel and meter.

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Finally, here are the record-shots for the run L60 unit.

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I think the previous owner put the stick-on rubber feet on the bottom. The kit manual mentions applying self-adhesive strips of cork to the raised areas on the bottom of the case, but I haven’t seen any meters that show evidence of that.

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Here’s the L60 unit with its WG-299E probe.

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