Forums :: NEW! Web Resources :: Features :: Photo Gallery :: Vintage Radio Shows :: Archives
Support This Site: Contributors :: Advertise


It is currently Nov Tue 24, 2020 2:53 am


All times are UTC [ DST ]





Post New Topic Post Reply  [ 59 posts ]  Go to page Previous  1, 2, 3
Author Message
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Wed 14, 2020 11:33 pm 
Member
User avatar

Joined: May Sun 10, 2020 2:55 pm
Posts: 528
Location: Bridgman, MI
nice i'll take one - the one thats works :)

_________________
only the dead fish go with the flow


Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Wed 21, 2020 6:05 pm 
Member

Joined: Jul Fri 10, 2020 11:10 pm
Posts: 268
I do have one of these. I don't know how to use it yet. I don't know if it works. Should I just go ahead and copy your restoration because it has to be done no matter what because of age of the components?


You work is outstanding btw.

Thank you,


Attachments:
1021201146_HDR.jpg
1021201146_HDR.jpg [ 763.27 KiB | Viewed 313 times ]

_________________
Greg
Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Wed 21, 2020 7:32 pm 
Member
User avatar

Joined: May Wed 18, 2011 2:40 am
Posts: 5065
Location: Littleton, MA
SX-42 wrote:
I do have one of these. I don't know how to use it yet. I don't know if it works. Should I just go ahead and copy your restoration because it has to be done no matter what because of age of the components?

No, you probably shouldn't tear into it too deeply. The minimum you need is to remove the battery before it leaks, check the meter to see that it's not burnt out, replace the electrolytic filter capacitor in the power supply, possibly replace the rectifier if it is a selenium type rather than a silicon diode, and replace any paper capacitors in the the circuit. In my examples, the non-electrolytic capacitors were either ceramic or modern plastic film types, so there was no need to change them.

You should check the values of the resistors on the PCB to see if any are open or way out of spec and, if so, replace them. Unless you have an ohmmeter that is accurate to 0.3% or better, you should leave the precision resistors alone unless they are very far out.

Unless you are pretty experienced, I wouldn't recommend disconnecting the range and function switches anyway, even if you have the gear to measure the precision range resistors accurately.

Then you're left with the problem of how to calibrate it. Ideally, you'd like a 50 volt DC supply and a 50 volt isolated AC supply, and a DMM to set the power supply voltages correctly.

Personally, I'd leave the battery out and use your DMM for resistance measurements instead. Too many of these have been damaged by battery leakage.

I can't see if your meter has the 0.5 volt DC range - that's a feature that's unique to the WV-98C model. If it's an earlier model, WV-98B or WV-98A, you'll probably encounter paper capacitors that need to be replaced, though I don't know because I've never seen the inside of a WV-98B, and I haven't started restoring my WV-98A's.

SX-42 wrote:
You work is outstanding btw.

Thanks!

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


Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Wed 21, 2020 9:23 pm 
Member
User avatar

Joined: Oct Sun 15, 2006 12:57 pm
Posts: 7288
Location: Liberty, Missouri
Its quite possible it works as is.

What does the labeling on the RED probe say? It may be that you have a "DC" probe, and an "AC/OHMs" probe.

If so, you can easily check the basic calibration using a few resistors, and a battery. For "DC" measurements, the original probe had a 1 Meg Ohm resistor at the tip of the probe, and the switch simply shorted out the resistor for AC and Ohms functions.

if you can find an original stock switchable probe for it you'll have a pretty good general purpose meter.

RCA sold thousands of these meters over the years, so finding a probe shouldn't be an insurmountable task.

Image

_________________
Pics, Bold & underlined text, are usually links.

https://mikeharrison.smugmug.com/

Mike


Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Wed 21, 2020 10:03 pm 
Member

Joined: Jul Fri 10, 2020 11:10 pm
Posts: 268
Thank you Steve!

This will definitely point me in the right direction. I will not take from your post further than to send a few more photos.
It does look like ceramic capacitors are in play.

Best,


Attachments:
1021201110_HDR~2.jpg
1021201110_HDR~2.jpg [ 622.03 KiB | Viewed 288 times ]
1021201114_HDR~2.jpg
1021201114_HDR~2.jpg [ 410.45 KiB | Viewed 288 times ]
1021201113_HDR~2.jpg
1021201113_HDR~2.jpg [ 426.07 KiB | Viewed 288 times ]
1021201113a_HDR~3.jpg
1021201113a_HDR~3.jpg [ 424.93 KiB | Viewed 288 times ]
1021201115_HDR~2.jpg
1021201115_HDR~2.jpg [ 940.55 KiB | Viewed 288 times ]

_________________
Greg
Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Wed 21, 2020 10:55 pm 
Member
User avatar

Joined: May Sun 10, 2020 2:55 pm
Posts: 528
Location: Bridgman, MI
SX-42 wrote:
Thank you Steve!

This will definitely point me in the right direction. I will not take from your post further than to send a few more photos.
It does look like ceramic capacitors are in play.

Best,


my eyes are not the best... but this looks like it needs more glue?


Attachments:
borDx1.jpg
borDx1.jpg [ 425.77 KiB | Viewed 285 times ]

_________________
only the dead fish go with the flow
Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Wed 21, 2020 11:47 pm 
Member

Joined: Jul Fri 10, 2020 11:10 pm
Posts: 268
Here is a blow-up of that area.


Attachments:
1021201711_HDR~2.jpg
1021201711_HDR~2.jpg [ 480.45 KiB | Viewed 278 times ]
1021201712_HDR~2.jpg
1021201712_HDR~2.jpg [ 618.47 KiB | Viewed 278 times ]

_________________
Greg
Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Wed 21, 2020 11:53 pm 
Member
User avatar

Joined: May Sun 10, 2020 2:55 pm
Posts: 528
Location: Bridgman, MI
I would re flow and clean those up

_________________
only the dead fish go with the flow


Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Wed 21, 2020 11:59 pm 
Member

Joined: Jul Fri 10, 2020 11:10 pm
Posts: 268
Hi Mike I think you told me about 3 months ago where to find probe sets.
So this is a vtvm test probe set. Please see the close up photo. It is new.

I haven't tried anything yet I just wanted to give it a once-over and confirm a few things before I try plugging it in. I need to do a lot of reading before I even attempt it. The national radio Institute complete course booklets are really good it just takes a little time to get caught up with what I want to do.


Thanks a lot guys if you have anything more that you can point in my direction I would very much appreciate it.


But I really should jump out of Steve's post before things get carried away. : - )

Best


Attachments:
1021201743_HDR~2.jpg
1021201743_HDR~2.jpg [ 322.37 KiB | Viewed 276 times ]
1021201743a_HDR~2.jpg
1021201743a_HDR~2.jpg [ 436.84 KiB | Viewed 276 times ]

_________________
Greg
Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Thu 22, 2020 12:41 am 
Member
User avatar

Joined: May Wed 18, 2011 2:40 am
Posts: 5065
Location: Littleton, MA
Mike is right, there’s a good chance it will work as-is. However, someone has already posted in this thread about a WV-98C with a toasted transformer, so I would replace the electrolytic before powering up. If the VTVM is basically working, then you can use the VTVM itself to check out the meter movement.

You should measure the resistors before trusting the readings. You only cal the meter on one range, and depend on the resistors being in spec for all the other ranges.

By the way, I see that your VTVM has a 0.5V DC range, so it is a WV-98C. It also has a selenium rectifier, which means it’s one of the earlier runs. Is there a run code stamped on the back of the case?

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


Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Thu 22, 2020 1:39 am 
Member

Joined: Jan Thu 01, 1970 1:00 am
Posts: 3631
Location: Seattle WA US
If both of those probes are connected to the mike connector at once.......when you apply voltage to one probe, the other unused one will be hot ! Yes, current limited by a 1 meg resistor, but still HOT.
-Chuck


Last edited by K7MCG on Nov Mon 02, 2020 11:24 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Thu 22, 2020 2:29 am 
Member
User avatar

Joined: May Wed 18, 2011 2:40 am
Posts: 5065
Location: Littleton, MA
K7MCG wrote:
If both of those probes are connected to the mike connector at once.......when you apply voltage to one probe, the other unused one will be hot ! Yes, current limited by a 1 meg resistor, but stil HOT.
-Chuck

Yeah, if I’m not making a switchable probe, I prefer to make two separate probes. I just replenished my stock of Switchcraft 2501F connectors, though, and they now cost almost $10 a piece! I can see the motivation for making Siamese probes.

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


Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Thu 22, 2020 2:58 am 
Member

Joined: Jul Fri 10, 2020 11:10 pm
Posts: 268
This is good probe knowledge. I will make sure I am well-versed before I even try to use them. Thank you.

The back panel marking is 5124K

Okay. I think I must now see the restoration of this voltOhmyst meter through to the end. I also need it so I can start on my SX-17 repair and gain experience along the way.

Thank you,


Attachments:
1021202004_HDR~2.jpg
1021202004_HDR~2.jpg [ 718.47 KiB | Viewed 248 times ]
1021202023_HDR~2.jpg
1021202023_HDR~2.jpg [ 568.69 KiB | Viewed 248 times ]
1021202019c_HDR~2.jpg
1021202019c_HDR~2.jpg [ 527.49 KiB | Viewed 248 times ]
1021202019a_HDR~2.jpg
1021202019a_HDR~2.jpg [ 523.28 KiB | Viewed 248 times ]

_________________
Greg
Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Thu 22, 2020 9:14 pm 
Member
User avatar

Joined: May Wed 18, 2011 2:40 am
Posts: 5065
Location: Littleton, MA
I think the "5124" is the serial number, and the run code is just "K".

I wonder if anyone knows what RCA's run code scheme was?

Between yours, Mike's, and mine, we have this so far:

K - s/n 5124
K114 - s/n 100324
K107 - s/n 125694
K117 - s/n 126564
L60 - s/n 137974

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


Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Fri 23, 2020 4:18 am 
Member

Joined: Jul Fri 10, 2020 11:10 pm
Posts: 268
That is a very good question. I am curious to figure this out.

_________________
Greg


Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Sun 25, 2020 6:37 pm 
Member
User avatar

Joined: Apr Thu 12, 2018 9:43 am
Posts: 451
Location: Fresno, CA
Steve these look amazing!


Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Sun 25, 2020 7:05 pm 
Member
User avatar

Joined: May Wed 18, 2011 2:40 am
Posts: 5065
Location: Littleton, MA
shawn1967 wrote:
Steve these look amazing!

Thanks Shawn!

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


Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Oct Sun 25, 2020 7:34 pm 
Member
User avatar

Joined: Jan Thu 01, 1970 1:00 am
Posts: 11073
Location: Omak,wa,usa
Hello Steve,
for years that was my go to meter when I wanted a VTVM .
After getting my Fluke 77 I kinda gave it away and want to get one for my bench right now I am using Heathkit model IM-11 .
The RCA unit is a nicer unit .
Sincerely Rich


Top
 Profile  
 
 Post subject: Re: Restoring an RCA WV-98C Senior VoltOhmyst VTVM
PostPosted: Nov Mon 02, 2020 4:48 pm 
Member
User avatar

Joined: May Wed 18, 2011 2:40 am
Posts: 5065
Location: Littleton, MA
Update #8

I started calibrating the run K117 unit. It was checking within spec on DC volts until I reached the 350 Volt cardinal point, when my HP-6920B meter calibrator went into current limiting. Uh-oh, my homebrew probe was breaking down at about 300 volts. I guessed there was some flux contamination that was breaking down.

It was a good lesson for me. I should be testing these probes on my General Radio 1862-B Megohmmeter at 500 volts before gluing them up, and running a 1500 Volt breakdown test on them.

Image
I fired up my General Radio 1862-B Megohmmeter and started testing my probes, but quickly ran into problems with the 1862-B. First, with nothing connected, the meter was reading well under 100 GΩ at 500V. I noticed some dust had collected on the binding posts and front panel, so I cleaned that up with electronics-grade isopropyl alcohol. You want to use anhydrous isopropyl for this, as the drug-store 91% has a bitterant added to prevent people from drinking it, and that often leaves a little residue that defeats the purpose of removing contaminants.

I was surprised to see how low the resistance went when the front panel and binding post were wet with isopropyl. When you’re measuring at the hundreds of megohms level, a lot of things have a little leakage resistance.

Second, after cleaning, the grid current was still too high for the highest range (100 GΩ at 500V, 10GΩ at 50V) to be usable. The manual mentions that “[g]rid current may be excessive if the instrument has not been used for some time; normal operation for ten minutes will reduce the grid current satisfactorily.” I haven’t used my 1862-B very much since I obtained it six years ago, and ten minutes wasn’t enough to bring the grid current down. I left it on overnight, and that did the trick.

Next, I cut open the probe to access the circuitry and the end of the cable. I used a razor saw to open the joint where I had glued the probe together. (I really should figure out a way to make these maintainable.) There was some flux on the proto-board, but cleaning that off wasn’t enough. I enlarged the gap between the pads where I had terminated the cable shield and the traces for the switchable resistor, and that helped considerably.

I then removed the Amphenol 75-MC1F connector from the other end of the cable. I trimmed the shield braid back a bit further from the end, and that brought the insulation resistance up to a satisfactory point.

Image
I glued the probe back together and applied new heat-shrink tubing as a strain-relief.

Image
The glue joint is pretty ugly but at least it works now. The insulation resistance from the connector shield ring to the probe tip is 110 GΩ. The resistance from the probe tip to the probe body is 50 GΩ. I put 1500 Volts between the connector shield ring and the probe tip and measured less than 100 pA of leakage.

I went back and checked my other home-brew probes, and fortunately they were all OK.

Image
I’d make another probe, but I’m out of the tiny slide-switches that I use for them. I bought them as surplus from Electronics Goldmine, and they sold out their stock of them years ago.

I’ve stocked up on some C&K ET01 surface-mount toggle switches from Electronics Goldmine, but they require a larger diameter probe. Evergreen doesn’t make anything larger than 1/2” diameter tubing. I’ve ordered 3/4” ABS tubing from Plastruct. It’s more expensive than styrene, but ABS is more rugged so it’ll make a better probe.

Image
Plastruct makes elliptical and semicircular domed ends for their tubing, so I'm going try using those for the ends for the new probe design.

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


Top
 Profile  
 
Post New Topic Post Reply  [ 59 posts ]  Go to page Previous  1, 2, 3

All times are UTC [ DST ]


Who is online

Users browsing this forum: Google [Bot], Jimmie Stewart, John Limbach, KB1VWC, PhilF and 15 guests



Search for:
Jump to:  




































Privacy Policy :: Powered by phpBB