Test Meters, Multimeters, voltmeters, ampmeters

Cliff Jones wrote:

I now understand the four-wire resistance method, it uses a voltage on two of the wires to eliminate noise and is better for low resistances.

hm..

hello Cliff,

They use 2 wires to put a constant current into the test R,
and another 2 wires to pickup the voltage on the Test R directly on it`s pins.

This makes shure that it is not important what resistance your test wires have, the result is trustful, also with mOhms.

Martin

in the logo from the forum, that seems to be a 200cd  

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Good Idea on the Batteries.

The HP 410C has the probe for Up to 400Mhz but will measure up to 1Ghz. but there are strict maximum voltages to observe. RF. It also uses a feed through for attaching between a dummy load or or antenna.

3-33. MEASURING DC NANO-AMPERE CURRENT
(Figure 3-.
3-34. The Model 410C can be used to measure nanoampere
leakage current in transistors and diodes. The
three most sensitive DC voltage measurement ranges
are used to measure DC nano-ampere currents.
I do have a HP 400E that is an RMS voltmeter, that I have yet to use

I have restorated a 427A.
it requires no special probe for AC.

Special problem was:  the obsolete 22.5v battery is actually too much expensive. It likes to work with 2pcs of 9v block lithium for smoke detectors, they provide 10.2v each, it`s enough for a 427A
The oscillator there is the 204B

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Additional information on the HP 410C, when the AC voltages are being measured, the multimeter provides D.C. voltage to the diode filament. In order to provide a reliable piece of test gear, HP designed the probe and multimeter to use A.C. voltage on the probe diode filament during non-use. This is accomplished through the voltage selection switch. 

In other words, when switching to the A.C. Measurement function, D.C. is provided to help eliminate hum, then when switched to a D.C. or RESISTANCE or CURRENT function the filament receives the required A.C. voltage to maintain optimum reliability of the probe, and that is why you will notice the probe is always warm when the H.P. 410C Multimeter is turned on.

I have an H.P. 410C, transistor/tube VTVM, 
but put it on a shelf because I didn't have the A.C. Probe for it. So that was 7 years ago. Probes for this Meter are as rare as it gets. I did get a probe that was used on a H.P. 410B, but the connector was totally different. It plugged underneath with a metal shell that contained a circuit card that used banana jacks and plugs for each, on the case.
The 410B uses a diode, that can be either a EA53 or a 2-01C. 

The EA53 uses a voltage of up to 7 volts. It is usually run at 6-6.3 volts D.C. The current draw is .3 amps.
The 2-01C uses a voltage of 5 volts, and was only used in the 410B. 
Because the 410B was adaptable to either tube, there was a switch internally that was used in conjunction with a ballast tube to meet the 5 volt need.

Well that complicated things for me as I didn't know which tube was in the probe, and hesitated to fiddle with the probe till I was more versed in its properties.

I bit the bullet last week and finally garnered the gumption to go for it.
The probe itself it a very well thought out design. It uses triaxial coax cable, which means 3 conductors, and two of them are used as shields and voltage carrying conductors at the same time.
The center conductor is in the R.F. path from the tip of the probe, with capacitors used in series and parallel to act as a bypass and shunt, and in turn hooked to the plate of the diode.
The cable has 3 insulators, one that covers the center conductor, and is clear nylon, then a woven shield covering that, then a thin black insulator over the 1st shield.

After that is a second shield, and that also is covered with black insulation sheathing.
The first shield is connected to heater directly and supplies the 5 or 6 volts.
The second shield is connected to the other end of return path and ground along with the cathode.

The tube itself is held in a barrel hole, and has friction fingers to make the connections.
I finally found a stereo jack that had a larger plastic end sleeve with a hole diameter that would accept the older larger probe cable. (That was very hard to find), and was a big holdup for Me.

I had to research the wiring of both 410B and 410C, and draw several diagrams to figure out the proper hookup. I finally used a meter to test which jack connector had the voltage while plugged into the 410C. It was the ring. The pin was for the signal, and the sleeve was the return and ground.

I needed to make an adjustment and that was kinda hard, finally I cleaned the plug and jack and rotated the switch several times before it would settle down. The last thing I did today was wire everything and bench test it. Still need to follow up with calibration. But that won't be to hard, I guess. 


If anyone wants the the manuals they are online, it also helps to get the tube data, and Hewlett Packard has a couple of papers on the two meters that made a big difference to Me, anyway.

Here's a nice tutorial that explains Dip Meters (GDO) and it usage. Grid Dip Meter.

I replaced a resistor that had been replaced before. They used two in  parallel  and the value was bad. All caps are newer. I calibrated it and put it back in the case.

If that uses the old copper oxide rectifiers, the odds are pretty good they have gone bad.
 Also replace the filter caps, and any other caps in the meter, and check the resistors.

I searched the site and found no information on the 209a VTVM. What should I do to repair this meter.
It turns on and the needle will center on D>C> Volts. I downloaded the original manual. It was easy to find. There are three rectifiers so I will check the filter capacitors first.

Here's a copy of the Field Strength meter instruction Pamphlet:

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I wasn't able to find anything on this Meter so I decided to post a copy of the Instruction pamphlet.


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I just purchased A fluke 8520A and paid a total of $75 including shipping costs.
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The  Multimeter has burst memory plus math capabilities. it was designed for system and bench applications, the Multimeter has 5 1/2 digit resolution and built-in system interface circuits.
A choice of:
1. DC,
2. True rms AC volts,
3, 2 and 4-wire ohms,
4. and also has a conductance . (The conductance function provides a simple way to measure resistance from 10 Mohms to 100,000 Mohms.)


Its Featuers include:

•520 readings per second which can be changed
•20 ppm basic DC accuracy
•IEEE-488 system interface

Note: to become stable on low ohms and volts it need to be on for 2 hours to stabilize the crystal oven and/or its processor.
I still need to learn the internal programing features.
and understand the 4 wire measurements.
I also need to learn how too make connector cables for the front input that will be reliable and how the internal and external guard functions are used.
It weighs over 25 Lbs.
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updated 06-16-2014
I have set my unit to measure resistance and all it would show is random numbers. I tried to reread the operators manual and didn't get any solution.
I went over the manual several times, and so I just said something's not right. I fiddled around with the switch buttons and all of a sudden it started working. Strange, so I set it up for the offset (to compensate for test lead resistance) but it took a few attempts to get it right. And it did work as expected. I did notice when it finally started working in the two wire mode that every time I changed resistors and applied the test leads I could hear a clicking relay. I turned it off and later I went back, turned it on and got the same results.

This is really weird so what I think is its not working right, because even if it is a lab standard, you should be able to get some reading for resistance right after turn-on. The only thing I can figure is the manual says it needs a two hour warm-up for accurate readings. Maybe it does have to warm-up for resistance readings, what do you think? Any one have experience like this with this model? It doesn't mention non-function time element. I see my voltage readings seem OK but now I will test that too when first turned on.
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I now understand the four-wire resistance method, it uses a voltage on two of the wires to eliminate noise and is better for low resistances.

About 53 minutes long, but interesting.

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Cliff, Funny this topic should come up… Some months ago I purchased a complete set of "The Impoverished Radio Experimenter" (a Lindsay publication) and it featured a rather extensive discussion of GDO's- their use, history and also instructions to make a nice solid state model.

Although I had some basic understanding of their use and function, it was rudimentary- at best. After reading the material, though, I realized just how useful a piece of equipment it is- especially when building from scratch (IMO, anyway).

Keep us posted on your adventures- I, for one, will be interested to hear.…

I also just had a Japanese Dip meter given to me by a Ham acquaintance. Its a Kyoritsu K-126B, and has 8 plug in coils. the frequency ranges are as follows:
Band A .435-.800MC BLACK
Band B .800-1.5MC BROWN
Band C 1.5-3MC RED
Band D 3-7MC ORANGE
Band E 7-16MC YELLOW
Band F 16-35MC GREEN
Band G 35-80MC BLUE
Band H 80-220MC WHITE

I just purchased a second hand Dip Meter from the Puget Sound Antique Radio Associations parking lot sale in Shoreline area. I couldn't go because of car troubles but my friend went keeping an eye out for certain Items I wanted. The Dip meter was one of them. Its a Kenwood DM-81 Dip Meter, It has another model for overseas called an Kenwood DM-801 Dip Meter.

It has some missing coils that I am searching for, so I Emailed Kenwood and I'll see what happens.
I may have to wind my own, not looking forward to that especially finding the supplies to do it.
I did get it for $20 and it works as I found out last n ight.
You can do a lot more with it than I knew. It is the solid state version so It uses an FET transistor and 3 diodes and a few transistors.
You can determine coil frequencies, inductance, use as a field strength meter, an absorption wave meter, RF Frequencies, Oscillator frequencies and even tune and trim antennas. It has a coverage of 700 Khz-250MHz however I am surprised it doesn't go down to I.F. Frequencies, I will look into that and see if it will by constructing a coil for that range. But It might work on the harmonics with out it, however on second thought, I will have to investigate that. There are a number of topics on the web relating to how under-rated the Dip meter is.
I have 4 coils,
#A (.7 to 1.6KHz)and
#C(3 to 7.4KHz) and
#E(17 to 42KHz)and
the highest frequency one I have #F (41 to 110 MHz) and it is a printed circuit coil.
So if any one has #B (1.5 to 3.6 MHz) and #D(6.9 to 17.5KHz) and #G(83 to 250MHz) please contact me, I will post an WTB (wanted to buy) in the Auction Floor forum.

Glad to hear you had success. From what your saying then, is in order to get a good voltage reading you had to have all the tubes in place and turned on. You can usually measure voltage from the bottom of the tube socket, just be careful of voltages and causing shorts. when you have the tubes in place if they are working as they should then you have a load on the transformer(s) that help bring the voltages into line.
Usually measurements are taken while on and operational, so when there is a problem you can Isolate section by section. Good call on your part, experience with trouble usually helps in the long run for similar situations such as this.

Hello All!,
I was trying to measure the voltage (following the voltage test points in the construction/instruction manual) and I was trying to do so with power on, but the tubes unpluged to get easier access to the pins. I was doing it all wrong!

Steve

Hello everyone, I am rebuilding some test equipment that was gifted several years ago. It all sat in the attic while I had kids, worked, divorced, remarried, etc. In short, LIFE got in the way. Now I am retired and working on it and I am trying to learn as I go.

The gentelman (now an SK) who gave this "stuff" to me was a very (in my opinion) knowledgeable guy and I wish he was still here so I could go to him for help. The 1st item I am trying to rebuild is a Knightkit VTVM (model 83 Y 125). I replaced a electrolytic cap and I am trying to check out the voltage on pin 1 of the 12AU7 tube. The book says it should be 77 volts. I have 153! I looked at all the reisisters and I thought I had three that had driffed and gone high. When I took them out of the VTVM, they each tested as they should! I went back to a web site and it says to test the Transformer as that is the unit that goes bad from "extended testing of shorted and leaky caps". The book does not show what the output is on the Transformer should be. One winding is 6.3 volts (heaters of the tubes). The other is 159volts. I am wondering if this is what it should be. Thanks for reading this.

Steve Myers

Hi Cliff, most of these Avo,s are 20,000 ohms per volt, whilst they do load the circuit to a degree, they were used here as the main meter in nearly all Service depots inc early TV depots, VTVM,S are used and have been quite a while i guess, the link below explains better than me ...regards....Alan.

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You will also fine that the older meters had lower resistance in some cases and you need to know that, because of the loading effect on voltage readings. In other words using a digital Voltmeter, has High input impedance compared to analog meters. However VTVMs are usually noted when doing certain required testing. Some meters are only 1,000 ohms per/volt. While VTVMs and digital meters are 10-11 megohms.

Most old radios were tested using a range of test meters from 500ohms to 20,000 ohms per volt.

Hi guy,s, i have digital display meters, and find for all old vintage radio sets here, the Avo Analogue meter was used to give all voltage readings in the Trader Service Sheets, i use my old Avo,s during radio repair and find them brilliant, my motto if its old the test gear has to be old to go with it, its more authentic this way....regards......Alan.

These voltmeters are more for Lab use and precision measurements. In part they have been replaced by Digital meters, but still can be useful. Not too many benches in radio repair use these but they are nice to have and show off.

The following is a comment I made on another forum (ARF) due to a question asking what are these used for.

In the simplest of terms it is has a voltage generator that has a bridge type metered circuit, so when the input voltage being tested matches the adjusted generated internal voltage,to indicate 0 when both voltages are the same.

The best effect is that when the voltages match there is no load on the circuit voltage being tested. They can be very accurate and precise.
(Ordinary VTVMs, VOMs and other meters will load down a circuit, some 1000 ohms per volt/ 10,000 ohms per volt, up to 11 megohms and even 20 meg ohms per-volt. If the voltage has no measurable current this can cause erroneous measurements.)

Here's a video that's about 18 minutes long, (see the link below my comments.)

It shows the steps for making a solid-state probe to replace the vacuum tube probe, by using a resistor, diode and cap, all inside a small copper tube. The problem was at first not able to zero the meter, then finding out there is is an offset resistor that compensates for the forward tube drop. that was replaced and with a 1 ohm resistor and now is working great. Very Educational and easy to do, even for the beginner.

Click Here no good now it goes to a used test equipment dealer

There are a couple (well actually three different types)  of Multimeter's.
The first used meters were designed with a specific task in mind.
It was found that the range of a meter could be increased by adding switches and resistors and shunts and batteries.
There were several descriptions used to identify the use intended.
Voltmeter to measure voltage in the range of a few micro-volts to several thousand volts
Ohmmeter to measure 100ths of an ohm to Millions of Ohms
ammeter measurements on the order of picoamps to hundreds of amps (amp-meter is incorrect usage of the term.)

Then when radio started to develop there was a need to have test equipment that was more versatile.
So functions were combined to create a VOM (Volt-Ohm-Milliammeter)
So came the development of the following types:

[You must be registered and logged in to see this link.]. Analog portable VOM
[You must be registered and logged in to see this link.]. Analog VTVM
[You must be registered and logged in to see this link.]. Digital VOM
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Then there are field units built for rugged use and then bench meters and Lab quality types.
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The first type has a mechanical meter movement to display numbers (analog style). When first introduced they had an input impedance ( or resistance) of 500 to 1000 ohms, they now can go up to the same as a digital. 10 or 11 meg-ohms.
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The second one came into existence because of the ever increasing need for a more accurate meter that wouldn't load down voltage readings.
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The third One uses computer chips and a digital screen to display numbers. They can have several functions built in. The Impedance input is usually 10-11 meg-ohms This is used to prevent loading the circuit under test.


The readings of a digital are more precise than an analog meter. An analog meter has a problem that is called parallax and is caused by reading the meter at an angle and therefore not getting correct readings. If there is anything else to add about Multimeter's, please feel free to post your thoughts and questions here.

You can ask or comment about Volt,amp,power, and other types of meters for the electronic repair field.