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 Post subject: Triplett 630-PLK - brand new, not accurate
PostPosted: Jul Wed 23, 2014 5:02 am 
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Joined: Jul Wed 23, 2014 4:52 am
Posts: 2
Hello everybody!

I have brand new, never used:

Triplett 630-PLK,
Type: 9

When reading DC voltage it is not accurate, for example if I measure 1.500V meter reads about 1.35V.
It is the same on all DC voltage ranges, it reads less than actual value. Did not check AC.
Resistance ranges are OK.

Does anybody have calibration procedure for this model? It is not included in service manual available online.
As far as I can see there is only one potentiometer available for calibration: R24A, above that I see 250mV adj.

Any help with this one?


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jul Wed 23, 2014 5:29 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 18544
Location: Albuquerque, NM 87123
If it is new then it should have some type of warranty. Where did you get it?


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jul Wed 23, 2014 2:48 pm 
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Joined: Feb Sun 02, 2014 9:13 pm
Posts: 1977
Location: Roanoke, VA
Johnnysan wrote:
If it is new then it should have some type of warranty.

It won't have a warranty - this is a ca. early '60s VOM which just happens to be NIB.

Zaoka -

What precisely were you measuring that should have been 1.5 volts but read 1.35 volts? Do you understand the loading effect of a 20,000 ohms per volt VOM?

BTW, where did you find the manual? The late-model copy that I have does not show an R24A.

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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jul Wed 23, 2014 3:09 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 18544
Location: Albuquerque, NM 87123
I don't think there is any real calibration procedure. You will probably have bad connections or bad parts. You should check all functions to get a better idea of what is wrong; if all ranges have a problem then I would suspect the protection diodes across the meter.


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jul Wed 23, 2014 3:26 pm 
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Joined: May Mon 18, 2009 5:55 pm
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Location: Erie, PA
It looks like there is a basic cal pot, R24A, that is listed as "part of the meter assembly," that would effect all measurements, but I don't know one would go about adjusting it. The model 60's I have more or less use the same setup, but that cal pot (along with a couple of others) is down on the circuit board. Both the 60 models I bought made in the 1980's needed to be re-calibrated.

http://www.triplett.com/wp-content/uplo ... 4-698e.pdf

-Mark-


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jul Wed 23, 2014 3:56 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2045
Location: Oswego, NY, USA
Ohms ranges might read alright even if the movement or protection diodes or connections have problems because the Ohms adj pots compensate for battery voltage loss and other losses, up to a certain amount. First, check the movement's 50uaDC full-scale deflection using the circuit diagram to guide you, directly across the movement with its protection diodes still connected. If that test fails, then disconnect the diode leg from the movement and recheck. If the diodes are good, they shouldn't change the meter reading very much, if at all, because you're not placing enough voltage across them for conduction. If movement reads less than 50ua fs then its armature, taut-band, or magnet has a problem. Then check the lowest mvDC range for fullscale deflection; calibrate it with the R24A if necessary..on most VOM's I've seen (I don't have a Type 9 to look at) it's a small wirewound trimpot attached in plain sight to the back of the movement case. Unlike Simpson 260's, most Triplett 630 series don't have a trimpot to adjust the movement's (50, in this case) uaDC deflection. Series 60's do have that trimpot, where their movement fullscale (w/o the trimpot shunt) is from 35 to 40ua fs.

From what I've read on a few Triplett-Jewell distributor sites, I think that in some cases the factory warranty is still good; what some distributors do is to replace a defective VOM with another nos unit from their shelf. The last few production runs, when they knew of the plant closing, didn't list the Bluffton address anywhere on the meter scale, but the manuals did because they were printed up far ahead. You might try contacting Triplett in Manchester to see if they might service or replace your "new" Triplett VOM, even w/o a warranty.


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 Post subject: hi
PostPosted: Jul Wed 23, 2014 8:50 pm 
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Joined: Jul Wed 23, 2014 4:52 am
Posts: 2
I was testing with DC source 1.500V, at the same time I connected my Agilent U1272A so 1.500V was accurate all the time.

I will open meter, make some pictures and get back to you guys.

I dont want Triplett to replace this meter since they dont make these anymore, I dont want 630 as a replacement because this one has relay protection circuit.


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jul Thu 24, 2014 12:34 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2045
Location: Oswego, NY, USA
Sometimes a PLK's relay contacts may need cleaning, which can cause calibration or repeatability problems. Swiping a crisp dollar bill (it's slightly abrasive and won't leave lint behind) across its contacts along with a little contact cleaner, sometimes helps. The relay can get sluggish or dirty if it sat on the shelf for months. If TTT-Jewell or a distributor did replace it, I would assume it would be with a like "nos" PLK, not a 630 which has no relay and sold at a lower price bracket.


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Wed 12, 2019 11:22 pm 
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Joined: Jun Wed 12, 2019 11:16 pm
Posts: 3
Location: San Jose, CA
I'm thinking of buying a Triplett 630 - PLK that the owner says about the same thing. He gets reading of about 10% less than actual. Sounds like this VOM had some issues with that sort of thing.

John M.
San Jose, CA
Retired US Army
K7CID Ham radio


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Thu 13, 2019 8:09 am 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 217
I have a Triplett 630-NA with a different problem. It's very accurate on all ranges I think. However something is wrong with the movement. When it is switched off, the pointer will not stay on zero. I can set the adjuster but when it gets on zero, it suddenly drifts off scale.

The same thing happens at full scale. If I try to zero Ohms, for instance, it will go right where I want it and immediately drift off to the pin.

I called Triplett about this and while they claimed to know all the ins and outs of this model, they had no idea about this problem.

Now that I am writing this, it occurs to me that perhaps the pointer is magnetized and is attracted by the limiting pin. It's a long shot and I have no idea how to fix this. When I have time and inclination I may open it and remove the pins at least temporarily, if possible, to see if there is something going on there. Otherwise it's a great meter, perhaps a bit bulky but has a marvelous plethora of ranges.

To obviate the need for that unobtainable 30 V Ohmmeter battery I drilled a tiny hole in the case and have an external supply using a wall power supply. It works great.


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Thu 13, 2019 11:04 am 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 18544
Location: Albuquerque, NM 87123
You can use three 9 volt batteries for the high ohms range; tape them together and they will fit in the case. You may have a static charge on the inside of the clear meter case; you will need to remove the 4 screws and wash the case.


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Thu 13, 2019 4:37 pm 
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Joined: Mar Sat 03, 2007 12:53 am
Posts: 738
It's possible to use a fine ink marker to mark the current position of the pot and to adjust it to see if it corrects the calibration of the meter. If it doesn't, then it will be easy to readjust the pot to the original position.


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Thu 13, 2019 6:53 pm 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 217
Yes three nine volt batteries will work but it's not an elegant solution. A meter with LeClanche batteries in it is corrosion waiting to happen. And surprise when you can't zero it after it sits on the shelf for a few months.

It's a cheap way out and I never liked the idea. These days, leaking batteries are much less of a problem than they once were but I still think there are better ways.

Of course, line operation destroys the portability of the meter, but when you carry a meter around you probably are measuring voltage anyway. If you need continuity testing you do need a source of power. And these Triplett units are not exactly shirt pocket models anyway. I have gravitated to cheaper units that don't eat up so much space on the bench. I have plenty of devices in case I need precise readings. So mostly the Triplett 630-NA and the Simpson 260 don't get used. They are the only instruments I have that will measure several thousand volts, however inaccurately. The Triplett actually goes to 6 kV and the Simpson to 5 kV. My other meters only go to 1000 Volts.

As regards static charge on the window, I have pursued that angle and that's not the problem. I will think about removing the stop pins to see if that may be it. Low priority project.


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Thu 13, 2019 7:46 pm 
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Joined: Jun Sat 09, 2007 8:14 am
Posts: 3679
Location: Florida
Upward drift of the multiplier resistors will cause low readings. A quick check for this can be done by measuring the meter's input resistance. The 630 is 20,000 Ohms per volt on DC so for the three volt range the input resistance should be exactly 60,000 Ohms, the 12 V range 240K, 60V range 1.2 meg, etc.

RRM


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Thu 13, 2019 10:33 pm 
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Joined: Jun Wed 08, 2011 2:33 am
Posts: 8724
Location: Ohio 45177
I think the old black one percent resistors did drift up some. I have some Heath decade resistances that have half percent black resistors and just about all of them changed a little, they may be within about 1% but no way within the half percent marking now. Still a one percent decade box is fine for hobby work. My 630 read a bit low and I found a resistor that was in series with the meter all the time on DC had changed a bit high. Something like 54 or 55K 1%? I forget. But I padded that resistor to make it read it's nominal value and the meter was notably closer on DC ranges. I wanted to pad all the resistors in the DC divider to try to bring the dial cal right on, but the further you go up the chain, the larger a resistor you need to effect a small percentage change and at some point who has something like 22 meg resistors lying around? I think the only adjustment in my old 630 is for AC or something. Well, I once had a 260 meter that was basically dead on, on DC ranges and that spoiled me. No 3% error nonsense!

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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Fri 14, 2019 4:36 am 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 217
I took apart the Triplett 630-NA and monkeyed with the movement and I think I have it repaired. For the first time in decades it works properly; I can read zero and full scale.

I am unsure just what I did to fix it, as I kind of cleaned it up and bent the stop pins and a couple of other little things, so I don't know which was the key to making it work.

But I am happy now.

Where can I find new rubber feet? They seem to shrink with age and no longer stay in the holes.


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Fri 14, 2019 6:32 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 2045
Location: Oswego, NY, USA
For replacement rubber feet/buttons, for Triplett 630 series bakelite case bottoms; some service trades carry the same buttons in their service kits; such as your local piano tuner....ask them, they'd be glad to give you the buttons, especially if you had them tune your piano (!). McMaster.com also sells them, if you're getting an order ready.


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Fri 14, 2019 7:02 pm 
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Joined: May Wed 18, 2011 2:40 am
Posts: 3924
Location: Littleton, MA
Fred Scoles wrote:
For replacement rubber feet/buttons, for Triplett 630 series bakelite case bottoms; ...
McMaster.com also sells them, if you're getting an order ready.

Thanks for the tip, Fred! I've been wondering how to get replacements. I'll have to measure the size when I get home tonight.

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


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Fri 14, 2019 7:27 pm 
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Joined: Jan Tue 10, 2012 8:39 am
Posts: 217
I couldn't find them in McMaster Carr. Maybe I didn't search properly.


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 Post subject: Re: Triplett 630-PLK - brand new, not accurate
PostPosted: Jun Fri 14, 2019 7:57 pm 
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Location: Littleton, MA
bob91343 wrote:
I couldn't find them in McMaster Carr. Maybe I didn't search properly.

I don't know the correct size, but this is the style:
https://www.mcmaster.com/9544k16

Search for "push in bumpers". The second grouping has the Triplett-style feet. They are style number 1, available in ID's of 7/32", 1/4", and 9/32". I'm guessing 7/32" is the right size, but I'll have to measure when I get home.

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