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 Post subject: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Mon 04, 2019 4:30 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1803
Location: Eagan, Minnesota, USA
Just bought an RCA WV 98C VTVM. The battery in my VTVM was removed, and there are two disconnected wires and a holder that just holds the battery with no connector provision. Should there be some kind of connector that slips over the battery or did they solder leads directly to the battery? If that is what they did, why would they not provide a connector for it and do this instead?

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Last edited by Frank on Nov Mon 04, 2019 10:03 pm, edited 1 time in total.

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 Post subject: Re: RCA WV 68C VTVM Battery holder.
PostPosted: Nov Mon 04, 2019 4:57 pm 
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Joined: Jun Sun 15, 2014 5:37 pm
Posts: 167
My RCA VTVM, I'm not sure of the model but more modern looking, had the battery soldered in. I assumed that was standard. It's there for resistance measuring, doesn't need changing particularly often.


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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Mon 04, 2019 10:08 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1803
Location: Eagan, Minnesota, USA
Just found a story about one that was new in the box. They took the back off and it does show the battery soldered in. That seems like a cheap way out for them to not include a holder for a replaceable part like a battery. Even my Radio Shack VOM has a battery holder for the resistance range.
Well, that's what they did, so I guess I'll just solder one in too. Maybe just solder a positive and negative lead to the new battery first, then solder those wires to the original leads in the vtvm, and slide an insulator over the connection. Next time it needs replacement, unsolder the connection and repeat the process for the replacement.

https://qsl.net/w0mpm/RCAwv98C.html


I have replaced the electrolytic 10 mfd capacitor, and I also replace the diode just for safe measure.
This is a nice unit, and I received the original paperwork for it. Very happy to have it!

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Mon 04, 2019 10:20 pm 
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Joined: Jun Sun 15, 2014 5:37 pm
Posts: 167
That's what I have. I didn't recognize the number. I also nevwr knew why it was a "senior" so I thought I was remembering wrong.

My first was given to me qbout thirty hears ago, someone.moving. Nice big meter on it. I.solid stated it, and added some circuitry to replace the battery, a few components off tge fikament winding.

About five years ago I found one on the sidewalk, just by itself in a box, on a very busy street, no sign of a repair store or obvious source.


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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Mon 04, 2019 10:55 pm 
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Joined: Jun Sat 15, 2019 7:43 pm
Posts: 273
Frank wrote:
Just found a story about one that was new in the box. They took the back off and it does show the battery soldered in. That seems like a cheap way out for them to not include a holder for a replaceable part like a battery. Even my Radio Shack VOM has a battery holder for the resistance range.

This was not a cheap way to connect the battery. In order to make accurate readings the battery connections have to make good contact, which they don't. It is not uncommon to find batteries soldered in test equipment.

DM


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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Mon 04, 2019 11:00 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1803
Location: Eagan, Minnesota, USA
That would explain it then.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Mon 04, 2019 11:51 pm 
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Joined: Jun Sun 15, 2014 5:37 pm
Posts: 167
That's a point. There's no easy access to the battery so reliability is important. If other things stop working, I immediately take off the battery cover and rotate the batteries in the holder, to clear up anything that might be blocking the voltage.


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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Thu 07, 2019 12:08 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4541
Location: Charleston, W.Va.
devilsmist wrote:
This was not a cheap way to connect the battery. In order to make accurate readings the battery connections have to make good contact, which they don't. It is not uncommon to find batteries soldered in test equipment.

DM

What 'devilsmist' says is very true, and there is also another reason:
These RCA VoltOhmysts (as well as much other test gear) were designed not only for the workbench, but also as portable instruments for use in the field or on service calls. This is why they have the carrying handles on top. This meant they were often transported/stored in service vehicles which were subject to vibration as well as frequent changes in temperature and humidity, all of which could compromise the integrity of battery contacts. Soldering the battery minimized these issues.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Thu 07, 2019 5:31 pm 
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Location: Ohio 45177
They are good quality meters otherwise, and I pondered the possibility of putting a holder of some sort in mine. If one would fit. It has a pretty old battery in it but still works OK. I have seen numerous problems with Simpson 260 where the low ohms will not zero as the D cell bronze contacts turn just a bit brown and the resistance goes up. Buff up the copper and it works fine. Like at least once a year. So that might be the issue they addressed. But soldering to cells is unappealing to me.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Thu 07, 2019 6:01 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1803
Location: Eagan, Minnesota, USA
This information about soldering the battery leads has been a big help. I have three other VTVM's that I would like to go through, and they all had the battery leads soldered. So now I understand that this was an accepted practice from the manufacturers that had a logical reason behind it.

I bought this meter and another WV 98C at our local radio swap meet last weekend. When I got them both home, this one was the nicer of the two. I took another look at the paperwork that came with it. There was a purchase order with a Western Electric heading dated 12/1969. It was placed into duty on 1/1970. Northwestern Bell is mentioned, and a building in St. Paul is also mentioned. The original warranty card was never sent in, and the original manual has a company stamp on it. All of the paperwork is like new, and in what looks like it's original envelope. The meter must have not had much use, because it's just about in perfect cosmetic condition. Nothing faded, scratched, marked up, etc. It is a survivor. I did a light cleaning to it, and waxed the case, replaced the 10 mfd electrolytic, and diode. Next I'll test the tubes (red lettered RCA's) and install the battery as discussed here. Lastly, I'll calibrate it and it will be good to use.

I'll get the the other WV 98C after this. This one has the newer 'RCA' logo on the meter, and the case is a light blue color with black knobs that differ from the other one. I checked it out inside, and it looks good. Should be ok after I go through it.

I could not find a decent WV 98C for years. Now I find two in one day! That's how it goes.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Thu 07, 2019 11:14 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 4541
Location: Charleston, W.Va.
Hi Frank,
Congratulations on finding two very nice ones. You are on the right track with the service work you have done on it. I doubt that you will find any problem with those RCA tubes; do not replace any of them unless absolutely necessary. Even then, follow the instructions regarding "aging" the tubes which are described in the RCA manual.

Regarding the battery: On my WV-98C and WV-77E RCA VoltOhmysts I still solder the battery in as per original. This is very easy and takes only a few seconds. But if you prefer, there is nothing wrong with installing a battery holder or battery clips onto the PC board. When the instrument is used only on the workbench, this should be perfectly fine.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Tue 12, 2019 6:09 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1803
Location: Eagan, Minnesota, USA
Update on the first of two WV 98C VTVM's. The first one is now completed. I tested the tubes, installed the battery, and performed calibration. It performs perfectly, and is now part of the equipment I use at the bench. This meter looks like it came out of the box! It was cared for, and I don't think it had much use in the past. I'm very happy with it.


Now, there is a second one I'm now working on. This one has the newer RCA logo in block letters. The case is a solid light blue color. The knobs are black with a chrome insert. I'm going to guess that it's possibly from 1974. There is a stamp on the meter case that has 7419 on it, so that's one clue for that date assumption. The circuit board looks just like the one in the other meter, but the components are somewhat different. This one has more carbon comp resistors on the board than the other one had. Going to have to check those out. Instead of RCA tubes, this one has a Mullard 12AU7A, and a Telefunken 6AL5. Now that is interesting. Either someone changed those out or for some reason, or they were supplied in lieu of RCA tubes. Not sure why RCA would do that. The white print is perfect on them, so they were either in there from day one or installed once as replacements. You know how that white paint comes off of those tubes from handling.

At some point, it looks like a battery was left in there too long and caused white 'dust' to land all over the metal plate that holds the battery holder and power transformer. This dust is only on that metal plate and luckily, no where else meaning, there is no damage to any switches, parts, circuit board, etc. So I plan on removing that metal plate and cleaning and sealing it with lacquer.

I decided to disassemble this thing as far as I could. At this point, the meter has been removed, and the front cover is off. I can now get to all of the components to test and if necessary, replace them. This will also let me clean everything to get it to look like new.

Before I disassembled it, I went through the calibration process just to see where things stand. It was a little off on the 50 volt test by a few volts, but overall, not too bad. So I know it works, and should work once it's done.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Tue 12, 2019 7:28 pm 
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Joined: Jun Fri 19, 2009 6:34 pm
Posts: 8931
Location: Long Island NY
The original reason for soldering the batteries in was because the meters draw considerable current on the low ohms range. Dirty contacts would give erratic readings. Soldering was more reliable.

One thing you need to consider is, those old carbon zinc D batteries of 40 years ago and further back had paper gasket seals. Soldering did not disturb them. Modern alkaline batteries have plastic seals which can be damaged by heating. Also, alkaline batteries typically have incredibly long shelf lives as long as they are not discharged. But when they are, look out! The chemical reaction on discharge eats through the cases rapidly and you get a gooey, corrosive mess in your once pristine VTVM.

On some meters I’ve extended the leads and put a battery holder on the outside back of the case. Some people do away with batteries altogether and make little power supplies that convert the heater voltage to 1.5 VDC, but putting the battery on the back is even easier. I can then keep an eye on the battery and easily remove it if the meter won’t be used for a while. I use one of the case screws to secure the battery holder so there are no new holes drilled and the meter can be put back to its original configuration any time I want.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Tue 12, 2019 10:39 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Charleston, W.Va.
Chris108 wrote:
. . .One thing you need to consider is, those old carbon zinc D batteries of 40 years ago and further back had paper gasket seals. Soldering did not disturb them. Modern alkaline batteries have plastic seals which can be damaged by heating. . .

The concern about soldering modern alkaline batteries that Chris108 mentions is valid. But this can still be successfully done provided one uses the following procedure:

First and foremost, you need a heavy-duty soldering iron which can provide heat at very high temperature, similar to what one might use in soldering to a metal chassis. An older Weller 250W-350W solder gun would be a good example. Clean a spot on each end of the battery and apply some paste or liquid rosin flux. Then tin the area leaving a small mound of solder. Using a very hot iron, you should only need to apply the heat for one or two seconds maximum, not long enough to overheat the metal ends(s) of the battery and damage its plastic seals.

Before installing the battery into its clip holder, bend the contact wires so that they firmly contact the previously-tinned areas. Then apply heat from your soldering gun (remember, only one or two seconds max!) and you will have a good joint without damaging the battery seals.

If you don't have a heavy enough soldering gun, then don't attempt the above procedure. Using light-duty soldering equipment will only heat the entire end of the battery, yet still not get it hot enough to make a good solder connection. And this will cause exactly the same damage to battery seals that Chris108 has mentioned.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Fri 15, 2019 4:22 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1803
Location: Eagan, Minnesota, USA
I found a problem. Resistor R4 is bad. It looks like it might have burned up. I put some pressure on it and it broke in half. Looks like there are black marks on it that might indicate that it was overheated.

The value is 9.75 ohms, 1 watt, 1%, and I think the manual said it was carbon film. Any suggestions as to what to use to replace this? I am guessing that this is critical to get right, and I don't think I have any resistors that exactly match this spec. Would appreciate some input on this.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Sat 16, 2019 12:30 am 
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Location: Littleton, MA
Frank wrote:
The value is 9.75 ohms, 1 watt, 1%, and I think the manual said it was carbon film. Any suggestions as to what to use to replace this?

A metal film 9.1 ohm 1% resistor is probably good enough. It would only throw off your low ohms scale a little bit.

Or, Mouser has a 9.53 ohm 1% resistor in stock for 93 cents:
https://www.mouser.com/ProductDetail/Vi ... Du82UQo%3D

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Last edited by stevebyan on Nov Mon 18, 2019 10:22 pm, edited 1 time in total.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Mon 18, 2019 6:30 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 1803
Location: Eagan, Minnesota, USA
Steve, thanks for the tip. Just placed an order at Mouser for that part and some stock for the shop.

Over the weekend, I spent some on this. It's all apart. I cleaned that white powder stuff off of the metal supports and put a coat of lacquer on them. I cleaned the two control pots with deoxit, and removed the bad R4, so it's ready to go when the new one arrives. (Instead of 9.7 ohms, it will be 9.53 ohms which is the closest match). The main circuit board is very clean so I just wiped it down. I checked the resistors on the board and they are all ok. The 1% resistors are still meeting spec. The case, knobs, hardware and meter has been cleaned, and will like like new when it's reassembled.

So it looks like replacing R4, the 10 mfd electrolytic, and diode will get done next and after that, assembly, testing and calibration.

I wonder what could have caused R4 to burn, and if anyone has any ideas, I'd like to hear them.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Mon 18, 2019 7:15 pm 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 809
Chances are that R4 burned for the same reason those always go. Someone applied voltage to the meter while on Rx1 range.

Had the resistor not opened, the meter might have been damaged, depending on the details.

It's wise to keep a few of those resistors around for when mistakes are made. The value of the resistor marks center scale on the Ohms range.


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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Mon 18, 2019 8:37 pm 
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Joined: Jan Thu 01, 1970 1:00 am
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Location: Eagan, Minnesota, USA
I did order two extra resistors just to have them in case something took another one out. It can happen where someone gets distracted and forgets to move the selector to volts and goes ahead with the probe taking measurements. So far, I don't see any further damage because of that. Hopefully that is the case.

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 Post subject: Re: RCA WV 98C VTVM Battery holder.
PostPosted: Nov Mon 18, 2019 9:21 pm 
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Joined: Jan Tue 10, 2012 8:39 am
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In every case I have seen where the resistor burns open, that's the only thing that needs replacing. Nothing else fails.


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