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 Post subject: RCA WV-98C, maybe or maybe not
PostPosted: Feb Sun 18, 2018 3:20 pm 
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Joined: Sep Tue 12, 2017 3:04 am
Posts: 45
Location: 251 Moon Lane Spring City, TN
I usually have good luck on Ebay, but this one is most likely a draw. She listed it as a WV-98C in working condition. When I got it the range switch was frozen and the 12AU7A tube was missing. However I notified her and she offered all my money back, I told her 1/2 back would be fine (she had paid $13 for 2 day shipping). And after all I'm in this hobby to fix things and learn.

Anyway look at the pictures, this meter looks like it's had a hard life, but I've looked all over the internet for the same pot. arrangement on the back and cannot find a manual that tells me which pot is which.

Good news is, the switch is unfrozen and a friend gave me a 12AU7 tube, the meter works, but needs some calibration.

Any help would be appreciated.


Attachments:
Front WV-98C.jpg
Front WV-98C.jpg [ 242.81 KiB | Viewed 264 times ]
Rear WV-98C.jpg
Rear WV-98C.jpg [ 236.62 KiB | Viewed 264 times ]
Case of WV-98C.jpg
Case of WV-98C.jpg [ 202.21 KiB | Viewed 264 times ]
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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Sun 18, 2018 10:41 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4067
Location: Charleston, W.Va.
Hi jhbowman,
The RCA WV-98C VoltOhmyst is a very good service-grade VTVM. I have used one for many years in my own service shop. They are not particularly hard to restore and calibrate, provided the meter is in good condition and there is no damage inside from leaky batteries. (These used a 1.5v "D" cell, clamped to the circuit board with wires "spot soldered" to the ends of the battery.)

The front panel of yours looks good. But I am puzzled by that orange-colored back which appears to be made of sheet metal. Every one of these I have seen had a cast-metal back painted in that same bluish-grey paint as used on all RCA test equipment, with a factory label applied to it.

You mention that your range switch in now un-frozen. Presumably you have used some type of penetrating oil or lubricant to accomplish this. Make sure you clean it all away using a non-residue contact cleaner. By no means allow any type of cleaner or lubricant to soak into the phenolic wafers of this switch.

Calibration of these is easy, but you need to obtain an original manual which contains full instructions. This manual will also contain a schematic diagram and complete parts list.

I don't understand your concern about the pot arrangement on the back of the board. To the best of my knowledge this was consistent throughout the production of the WV-98C, and should be fully covered in the standard owner's manual.

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Poston


Last edited by Poston Drake on Feb Sun 18, 2018 10:59 pm, edited 1 time in total.

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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Sun 18, 2018 10:54 pm 
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Joined: Sep Tue 12, 2017 3:04 am
Posts: 45
Location: 251 Moon Lane Spring City, TN
I tried pen oil to unfreeze the switch. I just wound up taking it apart. Pretty easy. The grease had turned to a wax like glue. Lacquer thinner on the bearing took care of that.

The problem I'm having is what you noted in your post. The meter, even though labeled 98C seems to be a Johnny Cash 1 piece at a time cadillac type meter. The pots aren't marked and no model I researched looks like it.


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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Sun 18, 2018 11:03 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4067
Location: Charleston, W.Va.
The meter scale on front is certainly original. And the meter pointer also looks original. Can you post a photo of the back showing the meter in question? In addition to the WV-98C which I regularly use, I have a couple of spare "parts sets" which I will be happy to open up and compare with yours. Is it possible that yours has been "cannibalized? That non-original back cover certainly is suspect.

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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Sun 18, 2018 11:44 pm 
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Joined: Sep Tue 12, 2017 3:04 am
Posts: 45
Location: 251 Moon Lane Spring City, TN
Poston Drake wrote:
Can you post a photo of the back showing the meter in question? That non-original back cover certainly is suspect.
The second photo above is the inside back of the VTVM. The case is metal and red.


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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Mon 19, 2018 12:27 am 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 3084
Location: Florida
The four larger pots on the back look like someone's klooge fix to replace the calibration pots, which are normally in a small four-section trimpot assembly. The homemade case is likely the result of the added pots making the whole assembly too deep to fit in the normal case.

RRM


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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Mon 19, 2018 2:29 am 
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Joined: Aug Sat 27, 2011 1:59 am
Posts: 51
Location: Kansas City area
Poston Drake wrote:
... The front panel of yours looks good. But I am puzzled by that orange-colored back which appears to be made of sheet metal. Every one of these I have seen had a cast-metal back painted in that same bluish-grey paint as used on all RCA test equipment, with a factory label applied to it.

I don't understand your concern about the pot arrangement on the back of the board. To the best of my knowledge this was consistent throughout the production of the WV-98C, and should be fully covered in the standard owner's manual.


I can't speak for the insides of any more than the one I own and the few I've seen demonstrated and calibrated on YouTube but, I'm with you, the OP's looks like a prototype in comparison. Maybe an early model? I have no idea. Totally blew my mind as far as appearance of the traces and the pots on the back. I'd like to see the component side of the board. I'd also like to hear what the date codes are on the tubes.

I just got one not too long ago. My tubes are original (with red paint dots on them) and dated both early, and late 1967. It seems to work ok but, accuracy could be better. I've found that more than half of the 1% tolerance resistors in mine are out of spec. So, that's another day's (or, year's) project.

Good luck with yours, jhbowman!


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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Mon 19, 2018 3:07 am 
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Joined: Sep Tue 12, 2017 3:04 am
Posts: 45
Location: 251 Moon Lane Spring City, TN
I decided to use the 98C schematic and probe the "switch" side of the pots to the plate of the 12AU7 tube. According to the schematic, the particular pot is only connected when the switch is in "its" specific position. On each pot at a specific mode setting , I got a 1k reading as compared to >10k readings in the other positions. So from that I'm think.......and mean think that that identifies the pot for that adjustment. Such as DC-, DC+ and AC. The AC balance was easy to find since it's connected to the rectifier. Through elimination that left the little pot at the bottom center and I guess it to be the .5 volt adjustment.
What's interesting is the pots don't look added, they look factory. Now some of the traces have been resoldered and the board looks like it took an electrical hit sometime in it's life. The bezel and case have to be from some other meter. I've looked at every RCA I can find and don't see that case or pot arrangement. So am wondering if the board and case are from a non-RCA.
The meter is now working well, but needs the zero adjusted badly on the AC. But it's for sure cobbled together. I think I read that all of these VTVM's were almost exactly alike. Although my Heathkit 4A is similar, but the meter is across the Cathodes, not the Plates.

Thanks for your help, if someone happens to ever see this post and recognizes the board and case, it would be nice to know.


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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Mon 19, 2018 12:33 pm 
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Joined: Nov Thu 07, 2013 3:29 am
Posts: 192
Location: Leesburg, Virginia
Very interesting. But if that's indeed an original 98C board it's been HIGHLY modified. I have several 98C of various serial numbers:
http://qsl.net/w0mpm/RCAwv98C.html

John

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W0MPM


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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Tue 20, 2018 1:28 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4067
Location: Charleston, W.Va.
jhbowman,
The plot seems to be thickening regarding your WV-98C. Certainly there are many questions about the one you currently have.

As I mentioned earlier, the RCA WV-98C VoltOhmyst is a good choice for a service-grade VTVM in your shop. But at this point I think I would would look for another one which is all original. You should be able to find one "on the cheap" (maybe for $10-$15 or even less at a swap meet or here in the ARF Classified) if in non-operating condition. Perhaps one with a damaged meter scale and/or bad cosmetics on its front panel, a cracked or damaged plastic lens cover, etc., but at least one whose case and internals are all original. Then between this new one and the one you currently own, you should be able to make up a good unit which would serve you well, and which will correspond with the published manual in terms of operation, components, schematic and calibration.

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Poston


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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Tue 20, 2018 3:47 am 
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Joined: Sep Tue 12, 2017 3:04 am
Posts: 45
Location: 251 Moon Lane Spring City, TN
W0MPM wrote:
Very interesting. But if that's indeed an original 98C board it's been HIGHLY modified. I have several 98C of various serial numbers:
http://qsl.net/w0mpm/RCAwv98C.html

John


John, I don't know much about making circuit boards, in fact nothing. But a friend of mine who has made them, says those traces look homemade. So here's the facts, the meter, faceplate and controls are most likely from a 98C. The circuit board was maybe homemade to repair a damaged 98C. But one question nags at me is the bezel. I don't know what a 98C's bezel is made of, but this one is aluminum. A couple of clues about it, is they screwed scrap strips around the bezel to allow it to align into the back case, also there is no hole to align the meters zero. If it is homemade, they had skill, for it and circuit board.

Keep in mind, this meter is working, although it needs a little tweaking to make it just right. Mainly the AC's balance or zero.

Poston, I have bought another meter and with my "new found" 98C knowledge ensured it has a blueish case and there is a hole for the meter adjustment. The rest is taking my chances again on Ebay.


Attachments:
circuit board crop 1.jpg
circuit board crop 1.jpg [ 137.55 KiB | Viewed 93 times ]
circuit board crop 2.jpg
circuit board crop 2.jpg [ 220.69 KiB | Viewed 93 times ]
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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Tue 20, 2018 4:11 am 
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Joined: May Wed 18, 2011 2:40 am
Posts: 3329
Location: Littleton, MA
The circuit board doesn't match any of my three WV-98C's. However, it appears the function and range switches are attached to your PC board, so I think it must either be an original RCA board or a quite sophisticated homebrew.

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Steve Byan http://www.byan-roper.org/steve/steve-at-play/


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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Tue 20, 2018 6:01 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4067
Location: Charleston, W.Va.
Perhaps we are "beating a dead horse to death" here, but I would still like to see a photo of the other side of that circuit board. I have owned and/or serviced several RCA WV-98's as well as WV-77's from this era; all of them had the typical light-brown colored phenolic circuit board, on the inside of which were crisp white printed lines outlining and describing locations of all components. Also, on this same side of the board every one I have seen also had the famous RCA lightning-bolt logo printed in white, as well as a date.

If the circuit board in this one does not have these features, it must surely be a homemade corruption. If so, someone worked hard to make it. And for what gain? Perhaps an instrument which functioned OK at the time, but was sure to present issues to anyone else who obtained it in the future.

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Poston


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 Post subject: Re: RCA WV-98C, maybe or maybe not
PostPosted: Feb Tue 20, 2018 1:06 pm 
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Joined: Sep Tue 12, 2017 3:04 am
Posts: 45
Location: 251 Moon Lane Spring City, TN
Poston, "crisp white printed lines outlining and describing locations of all components
The board has none of these, I wish I had a picture, but I've given it to a friend. Anyway the tube side is just plain brown circuit board with the resistors and tubes mounted.
I did try to contact the lady that sold it, but she said she didn't know and was not in contact with her husband any longer. But the printing on the circuit board seems to prove, it's not an RCA board, at least not retail.


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