EEVblog #634 - Analog Multimeter Teardowns

[EEVblog]

Teardown Tuesday.
3 classic analog multimeters:
Metrawatt Unigor A43: http://www.haw-hamburg.de/fileadmin/user_upload/TI-IE/Daten/Labore/Elektrotechnik/Bedienungsanleitungen___User_Manuels/UnigorA43.pdf

Triplett 630NA: http://www.triplett.com/wp-content/uploads/2012/11/84-183f.pdf

Simpson 260 XLP http://www.simpson260.com/260-6/simpson_260-6xlp.htm

[kizzap]

Well there is the multimeter shootout for the year over and done with! 

That Triplett was a damn fine looking meter inside

[Bored@Work]

If the label on the Unigor doesn't say BBC Metrawatt, but just Metrawatt, then that particular meter must be from before 1968. In 1968 BBC bought Metrawatt and they became BBC Metrawatt.

That also matches the age of other Unigor meters, the Unigor design series originated in the early 1960th.

So you are looking at a 45+ year old meter, still in spec. and where they did manage to get the pin spacing right - as opposite to that second meter 

[vk6zgo]

What?
No AVO 8?

[EEVblog]

If the label on the Unigor doesn't say BBC Metrawatt, but just Metrawatt, then that particular meter must be from before 1968. In 1968 BBC bought Metrawatt and they became BBC Metrawatt.
That also matches the age of other Unigor meters, the Unigor design series originated in the early 1960th.
So you are looking at a 45+ year old meter, still in spec. and where they did manage to get the pin spacing right - as opposite to that second meter 

Ah, thanks. In that case I'll cut it some more slack!

[MaxTesla]

Hey Guys and Dave

As my Dad owns quite an old multimeter made in USSR, I thought i should share some teardown pics with you

I don't know how old it is exactly, my guess is as it is made in USSR and my dad did his apprenticeship back in 1970, that the meter must be at least 40 years old.

Hope you are enjoying the pics
On the back side of the meter there are some instructions how to measure stuff, the input sensitivity (DC range 20kOhm/V ; AC range 4kOhm/V) and the burden voltage (DC 0.4V ; AC 1.0V)

I am sorry for the bad lighting condition of the pics, my workspace is in my basement

Regards,

Max

[david77]

Here's a scan of the "RIM Electronic 1976" catalog pages concerning the Unigor A43 and its bigger brother the Unigor 6e.
The A43 is still a very common meter on ebay or on local flea markets, the 6e is much rarer, wich is understandable as it cost double the price of the A43. Note that one is sold a Metrawatt and the other under the Goerz brand name. After seeing Dave's
teardown it is clear that the same construction style was used on both these meters. Not only the outside looks extremely similar.

I do have a 6e in good condition, it's my goto meter whenever I want to use an analog meter. From a modern POV the build quality might look atrocious but considering that these meters were probably designed in the 60ies and were probably the first generation using PCB's, one shouldn't be so hard on them. They do still work after 40+ years, to me that is a sign of quality.

Can anybody shed some light on how BBC (Brown Boverie & Cie, not TV station), Goerz and Metrawatt were involved?

PS: Sorry, scans are in German.
PPS: Just looking at the technical data for the 6e I noticed it mentions the burden voltage in the amps ranges. There wouldn't be much point in Dave's µCurrent if modern meters were that good.

[RupertGo]

I think the 'trimmer resistor' at 26:10 is a compression trimmer capacitor; I remember tweaking banks of those things when aligning old communications receivers back in the day. I guess that's C3 in the Triplett circuit diagram, but I can't make out what it does - something to do with the capacity measurement? Which looks a lot of fun - whamming 110 VAC mains voltage across a capacitor divider to work out the DUT! That's a very macho way of doing things: none of that weedy internal oscillator nonsense for Real Engineers...

[david77]

...
Which looks a lot of fun - whamming 110 VAC mains voltage across a capacitor divider to work out the DUT! That's a very macho way of doing things: none of that weedy internal oscillator nonsense for Real Engineers...

The ICE Supertester 680R does that too. It's supplied with a 230V mains lead for capacitance measurment. Always made me kind of nervous...

[Cottees]

I have a Jayem JK-20K. It was my grandfather's. I think it was Aussie built.

[Towger]

What?
No AVO 8?

I have a broken military version, I was planning to send Dave soon. It is old and crusty just like how Dave likes his vintage electronics. The smell of musty old electronics off it would take your breath away :-)

Only problem is the postage is about 50 euro...

[Radio Tech]

Nice tear down Dave.
I love old meters.
Here are my two Simpon meters. The one on the left is a series 6PM (1973 vintage). On right series 6XLPM (1978).
Both of these meters have the mirror.


The third one is a Simpon wanabe, my old Micronta 22-220 (1978??) From when Radio Shack was a real electronics place!
Link to Micronta
http://www.radiomuseum.org/r/radio_shac_micronta_electronic_mult.html

[EEVblog]

I think the 'trimmer resistor' at 26:10 is a compression trimmer capacitor

So it is. Completely missed that in the schematic.

[EEVblog]

The third one is a Simpon wanabe, my old Micronta 22-220 (1978??) From when Radio Shack was a real electronics place!

I have one of those and was looking for it before the teardown but couldn't find it!

[Radio Tech]

I have one of those and was looking for it before the teardown but couldn't find it!

Funny 
I was just about to hit post on the two Simpson's when I remembered I had the Micronta. So threw it in as well.
China quality at it's best.

[Stonent]

I've got an early 80s Micronta with the range doubler. It has a nice hickory smoked .46 ohm resistor inside with the wires exposed from when I tried to measure a car battery on the milliamp or ohms range accidentally.  The video explains the unobtanium in these resistors.  I could get an smd resistor in that value 0805 I think but it was 6 or 7 bucks.

[WackyGerman]

Hi Dave ,
thanks for the interesting teardown of good old analog stuff . So here is my ABB Metrawatt Metravo 4 s with rubber holster , built in 1976 . It s a little better than the unigor and it has 1333 Ohms/V

[quarros]

That Unigor meter to my knowledge had at least two different version/manufacturer. One is made by Metrawatt and the other is by Ganz. I dont know who copied who but aside from the case of the meter, the inside of the two was very different (2 board construction to 4).
Interestingly even now the Ganzuniv is a crazy expensive equipment, a refurbished one is cost at least 420 AUD



Pictures of the inside:
http://regimuszereklhanzi.5mp.eu/kepgaleria_nagyitas.php?azonosito=regimuszereklhanzi&oldalkod=ErgPrYxc0Y&kepkonyvtar=&kep=06..jpg

Ganz: http://en.wikipedia.org/wiki/Ganz_Works

[linux-works]

I bought one of these just a week or 2 ago:



and even a 2nd one since I liked it so much.  I'll open it open it up and take some teardown pics of them.

they are nice cute little meters.  still a current model even after 50 or so years!

[Radio Tech]

I bought one of these just a week or 2 ago:


and even a 2nd one since I liked it so much.  I'll open it open it up and take some teardown pics of them.

they are nice cute little meters.  still a current model even after 50 or so years!

I have one almost the same. It is the 310-TEL
These were designed for the telephone repair man. Voltage only goes up to 300 volts AC/DC.
 On the top is a place to connect the lanyard  to hang yourself with.  Also has a polarity switch on the side.
I like mine and use it often.

Thanks for sharing.

[linux-works]

the polarity switch is nice.  neither of mine have it.

one that I bought came with the ac clamp.  I can't seem to get my clamp to read anything, but maybe I'm not using it right.

there are some that are marked as 'bell system' and some that were even made and marked with 'ibm', sort of how fluke made some of its handheld dmm's for ibm.

the little mighty-mites are not light   when I hand mine to people, they are always surprised at how heavy it is, for its size.

[Radio Tech]

the polarity switch is nice.  neither of mine have it.

one that I bought came with the ac clamp.  I can't seem to get my clamp to read anything, but maybe I'm not using it right.

there are some that are marked as 'bell system' and some that were even made and marked with 'ibm', sort of how fluke made some of its handheld dmm's for ibm.

the little mighty-mites are not light   when I hand mine to people, they are always surprised at how heavy it is, for its size.

Good info.
I agree, these things feel like bricks.  Can you imagine having this hanging around your neck all day? When I worked in the mobile communication field and had to go out and service 800 MHz trunked radio systems the Tel-Co folks would always meet me at the tower sites with these things hanging around their necks.  I was really surprised how much they weighed.
The polarity switch was a nice feature also.

[WackyGerman]

yes they feel like bricks , also my metravo 4s . but my greenlee dm-a 830 is really huge and heavy too . i think the cat IV 1000 V rating is the reason for it . it s built really solid , could be used also for self defense 

[elliott]

The Triplett's protection diodes are in a single package, it is that gold leaded brown component on the back of the meter movement. I have a pair of 630As, I'm jealous of the NA's range doubler. I also have a 630-PLK with the overload reset, but it was beyond repair due to corrosion of the range switch.

You can hurt a Triplett, I'm not sure how because it was done before I got it, but you can burn those unobtainable precision resistors.

[Thilo78]

Dave, as I just commented on YT:
If you don't like the Unigor, I'll be happy to give it a caring home 

I have my somewhat-80s Unigor A43 (manufactured in the time when Goerz Metrawatt was part of BBC) and I love to work with it.
I saved that one from the junk bin in the education lab at ABB, when I was a freshman with ABB in Mannheim.

It would only need a little adjustment. Still have to figure out the bunch of pots to adjust it. 

Greetings

Thilo

[Bored@Work]

That Unigor meter to my knowledge had at least two different version/manufacturer. One is made by Metrawatt and the other is by Ganz. I dont know who copied who but aside from the case of the meter, the inside of the two was very different (2 board construction to 4).

I wouldn't say they are so different. More like a different model from one product line or an earlier model. E.g. the nicely straightened and bend wires inside, the protection switch, the warranty sticker with the blue border, the technique with the wires for connections between boards are just a few of the similarities.

And after thinking about it, I remembered something. We previously had a case where we found that a eastern European company (Iskra) was building meters for Metrawatt, from the Unimer series.

Maybe Metrawatt also hired Ganz to build multimeters for them.

https://www.eevblog.com/forum/reviews/old-iskra-unimer-2-%29-%28metrawatt-clone%29/

[quarros]

I wouldn't say they are so different. More like a different model from one product line or an earlier model. E.g. the nicely straightened and bend wires inside, the protection switch, the warranty sticker with the blue border, the technique with the wires for connections between boards are just a few of the similarities.

And after thinking about it, I remembered something. We previously had a case where we found that a eastern European company (Iskra) was building meters for Metrawatt, from the Unimer series.

Maybe Metrawatt also hired Ganz to build multimeters for them.

https://www.eevblog.com/forum/reviews/old-iskra-unimer-2-%29-%28metrawatt-clone%29/

That could certainly be the case. One of my friends told me that most of these types of multimeter's  (ones with similar case's) are a copy of the Ganzuniv. But I was unsure if I could believe that.

[128er]

Here are a few pictures of my only analog multimeter.

-Measures up to 100A AC/DC and 1000V AC/DC. 5 kOhm/V.

-Resistance measurements up to 10 kOhms.

-Accuracy is +/- 1,5% for AC/DC ranges and +/- 2,5% for resistance (full scale deflection).

The HRC fuse was replaced with a wire when i got it and it is still    .  The opamp is a LM4250. It is presumably built in the late 70s to early 80s. Weighs about 1 kg.

Manual (only in german, but with scematic):
http://www.directupload.net/file/d/3176/v7wddy63_pdf.htm

[balu]

Hi Dave,
Thanks for the great teardown of good old analog Multimeter. I have an old Multimeter C-4317 (?-4317, Manufacturer: Mashpriborintorg ) from USSR. It works absolutely fine today and is assembled August, 1977.

I’m not sure, but I think the design of the UNIGOR A43 is made by HFG Ulm (Ulm School of Design in Germany 1946...1953, follower of the Bauhaus 1909...1933).

http://en.wikipedia.org/wiki/Ulm_School_of_Design
http://en.wikipedia.org/wiki/Bauhaus
http://www.hfg-ulm.de

Pictures of the C-4317 Multimeter:

[josko]

My favorite is Czechoslovak Avomet II DU10 made by Metra Blansko, it's been in production from 1953 until at least late 70's.
Really rugged meter (heavy bakelite case) and fine movement.

The interesting think that there is not single range switch, but three separate for Volts, Amps and Ohms and you can select range switch by pushing it down, really neat, I've never seen this kind of construction elsewhere.

Of course being 50's vintage it's all point to point construction...

Pictures:



Details: http://www.radiohistoria.sk/Oldradio/main.nsf/wcatalid/0006065

[Flump]

great video dave
i took apart one of my analog meters while watching it!

I think I have about 11 analog ones now but this one is
more similar to the unigor than the others are

[BobC]

Please keep reminding us to do the "Thumbs Up".  When you say it, I do it!

[denelec]

Here's a quick teardown of my 30 years old Micronta 22-204C from Radio-Shack.
It's a 50 000 ohms/V meter.
The rated accuracy is 3% on DC and resistance and 4% on AC.
It's made of very brittle plastic.æ

[denelec]

Sorry, somehow, the pictures didn't follow...
This meter WASN'T made for an industrial environment.

[Stonent]

Sorry, somehow, the pictures didn't follow...
This meter WASN'T made for an industrial environment.

Yeah that's my meter except yours is in much better condition, for example, yours still has unburned resistors and the metal part that gives you an indication of what range your knob is set.

[linux-works]

I loved that micronta radio shack meter with the range doubler.  it was my first new meter and I built mine as a kit.  lasted a long time but the case wasn't very strong and it started to crack, over time.

but it was affordable and great for a teenager, just starting out   I think I got mine in the late 70's.

[calin]

I have to Troiplett 630 , one exactly as dave's and one same but no 6KV .. got them few months ago of the bay for ... 12$ both. It was literally an stumble upon buy case .. They are both spot on, batteries still good etc. Owned before one by Raytheon and one by Hughes Aerospace .. yeah that Huges . Indeed these Triplett meters are a piece of art ... not to mention that they still work good, I still use them from time to time. The one that can do 6KW came in pretty handy when I worked on restoring an old Tek 475 .. which unfortunately still waiting for a CRT.


I left the cal sticker  on the Hughes one just for historical reasons


Now here is my 2 cents question. I just bought a  HP 6112A PSU made in the 60-es , and the PCB plus board layout are awesome (2 sided through hole design) neat and clean. Now .. why the hell thse meters are all built so crusty compared to that .. they are from same era right ? 


I curious yes I got the PSU working ... some pictures here. https://www.eevblog.com/forum/testgear/harrison-high-stability-lab-psu-with-oven-stabilized-voltage-sense-hp-6102a/msg463854/#msg463854 

[petertux]

nice teardown Dave and also very nice pictures in this thread, keep them coming guys!

I thought I'd share pictures of my soviet TL-4M multimeter.
it can measure 0.1-1000V dc/ac, 0.3mA-3A, 100uA, 1-10kohm and transistor currents.

[zaoka]

Here is one of best Japanese analog meters of that time.  HIOKI M-230A

I did not take a picture of the protection relay at that time...

In catalog they said that this meter was exceeding Japanese military standards at that time. If I remember correctly it is 1.5% tolerance for DC.

[tekfan]

great video dave
i took apart one of my analog meters while watching it!

I think I have about 11 analog ones now but this one is
more similar to the unigor than the others are

Is that a Russian Z4300 series multimeter?

[zapta]

Analog multimeters bring a lot of memory. Got my first one in elementary school, it didn't last a day, I connected it to main voltage while in the wrong range, my dad took it to the local electrician but he did not know how to fix it.  My next one was a good quality 20kohm//V Sanwa that served me for years. At the time I was building digital phone dialers and the analog meter was very useful to count the dialing pulses. Later used big ones professionally, we used to call them 'avo' regardless of the manufacturer and model just like 'fridge'.

Not using or owning any now. Between a digital DMM and a DSO I have everything I need.

[rsjsouza]

The ICE Supertester 680R does that too. It's supplied with a 230V mains lead for capacitance measurment. Always made me kind of nervous...

I remember taking some shocks from one of the leads of my dad's 680R when trying to measure capacitance, frequency or the ohms x 10000 range... not fun.

[Chryseus]

Here's a Japanese made TMK 700 I pick up a little while ago off ebay.
Gotta really love the build quality in these old meters

[david77]

If you're really into old and very old T&M gear have a look at this site

http://www.historische-messgeraete.de/index.php

Now there's somebody with a real fetish!

As far as I can tell it's only available in German but the pictures are good enough  .

[elliott]

I think I might have a good solution to the 30V battery for the Tripletts. An 18650 Li-Ion cell fits perfectly into the original battery holder. Plenty of room for a small DC-DC converter in these things too.

[david77]

Here's my oldest analog multimeter the Multavi 5, made by Hartmann & Braun sometime in the late 50ies. It used to belong to an old electrician who used it throughout his career but luckily always took good care of it.
It is one of the better instruments of its time with 1% fs accuracy in the DC ranges. You can also connect it to measure volts and amps at the same time making power calculations easy using only one meter.

The last picture shows my oldest piece of T&M gear, a Siemens & Halske amp meter, it does 0,1/1/10ADC. It's got a date stamp inside showing it was built in 1943 and it's still pretty much spot on, this meter is really quite useful and of all my analog meters I use it the most.

[Tothwolf]

If the label on the Unigor doesn't say BBC Metrawatt, but just Metrawatt, then that particular meter must be from before 1968. In 1968 BBC bought Metrawatt and they became BBC Metrawatt.

That also matches the age of other Unigor meters, the Unigor design series originated in the early 1960th.

So you are looking at a 45+ year old meter, still in spec. and where they did manage to get the pin spacing right - as opposite to that second meter 

Based on the package type of those two diodes I was thinking early to mid 1960s, too. Tag strips and other point to point construction designs would have still been common construction techniques when this meter was made, so the use of pc boards would have still been seen as novel and more "cutting edge" for a multimeter.

I have an earlier Simpson 260 (I think either series 3 or series 4) that seems to date from around the same time period as the Metrawatt, and it's pc board seems just as "crusty" in design. It looks similar to these: http://simpson260.com/260-3/simpson_260-3.htm http://simpson260.com/260-4/simpson_260-4.htm

Dave, is there a date printed anywhere visible in the Metrawatt meter?

[MatthiasBerlin]

It seems that it's still possible to buy slightly updated multimeters of the Unigor series from that company Ganz in Hungary mentioned before:
http://www.ganzinst.hu/wp-content/uploads/2013/05/Ganzuniv.pdf
These similarities simply cannot be pure chance...

Maybe they'd like to send Dave an up-to-date version for a teardown?

[Steffen]

I remember, 2008 during my vocacional trainig (I was 19) I also was suggested to use an old Simpson brand analog multimeter for repair jobs. It was quite easy to find defective transistors inside an old 6,5V 80A linear power supply (Rack mount 2U). That device contained not less than 15 2N3055 all mounted in parallel with balancing resistors. It was a heavy device with many faults. I replaced about 4 transistors, but could not proceed to test, because that repair shop did not have a dummy load to test this device under maximum load. In the cabinets, we also have some Multavi 5, but they are not used anymore, even if they still work.
The most impressing battery life i've ever seen was inside an old Rode & Schwarz URV. That device was maybe 30 or more years old, but the battery was still nearly full. With growing frequencies and more modern digital power meters, the URV has also become obsolete.

[G7PSK]

I took some photographs of my AVO 7 Panclimatic. It is supposed to be usable in the tropics, its ex RAF. so I suppose they need to be able to operate in all parts of the world. The meter is sealed with an O ring between the metal back and the Bakelite front and the battery box which comes out with the back unit connection being by 3 brass springs.1% on DC and 2.25% AC also has capacity using 50 HZ mains at 100 to 250 volts it also measures up to 40 M ohm using up to 900 volts DC or AC.

[pgross]

Hi Forum,

Just want to chime in with some photos of my Old - but still perfectly fine Goerz (Metrawatt, BBC) Unigor 6e multimeter.

This model will NOT measure voltage or anything without 4 pcs. C size alkalines installed to supply power to the input amplifier.
In order to obtain the impressive (1973 vintage) input resistance of 10 MOhm in the 10-1000 V range and capacitance measurements from 50 pF up to 2000 uF,
no less than one dozen bipolar transistors and two fets are incorporated into the meter. 

I guess that some old heavy bearded guy from Austria not Australia, did have some  on the trimmers inside. 

Anyway - here follows the pictures of its guts:






   

[retiredcaps]

Ebay Triplett 630 teardown. 

http://www.ebay.com/itm/251569828882

[elliott]

Ebay Triplett 630 teardown. 

http://www.ebay.com/itm/251569828882

Good deal if you need some resistors to repair another one, it costs about $12 just to ship one of the beasts complete in the US. I ended up buying 3 of them basically for the cost of shipping and made 2 working ones out of them.

[Lefuneste]

I think I might have a good solution to the 30V battery for the Tripletts. An 18650 Li-Ion cell fits perfectly into the original battery holder. Plenty of room for a small DC-DC converter in these things too.

I was thinking about this modification too as these 30V batteries are a real PITA to find, but won't the step-up stage introduce some HF noise into the meter ? These small step-up boards are all switching voltage converters. Obviously it's going to be in the hundreds of kHz range so maybe the good old Triplett won't move an eyebrow about it. Any idea about that ?

[Lefuneste]

Hi Guys. Just a quick follow-up... question...
I have scored a Triplett 630 (APL version) out of the Bay yesterday as these VOM are so damn sexy. I was wondering about the probe connectors on them. I'd like to get some probe master probes for it (absolutely amazing probes by the way, Thanks for the mailbag review Dave !!). I am wondering what type of diameter the 630 accepts. I understand that shrouded connectors are not an option on these ancient meters, but the diameter and length seem also weird. Maybe it's just my imagination... Does anyone know if it would accept non-shrouded 4mm connectors ? Do they have to be in specific shorter length as well ? Any clue about that ? Thanks for the info !!

[elliott]

I was thinking about this modification too as these 30V batteries are a real PITA to find, but won't the step-up stage introduce some HF noise into the meter ? These small step-up boards are all switching voltage converters. Obviously it's going to be in the hundreds of kHz range so maybe the good old Triplett won't move an eyebrow about it. Any idea about that ?

Haven't got that far into it yet, I've only run mine off my linear bench supply. I'm encouraged by the fact that the battery fits nicely, I'll probably get one of those cheap eBay boards and try it out. Since I have two I can power one from the bench supply and one from the lithium with the step-up and compare. I can use one of those spare 0.5% 4.5Mohm resistors I have from a parts meter as a reference.
 

I was wondering about the probe connectors on them. I'd like to get some probe master probes for it (absolutely amazing probes by the way, Thanks for the mailbag review Dave !!). I am wondering what type of diameter the 630 accepts.

Every 630 has 4mm jacks as far as I know, the Triplett 310 had 2mm. I haven't had problems with anything I've stuck in them, including some cheap shrouded probes I cut the shrouding off of.

Triplett made some awesome probes, I have an original set that is still serviceable. They are needle sharp and have screw on alligator clips. They are so nice I am going to disassemble them and replace the wires, which is easy to do. It is a shame that I'll lose the original "T" branding on the plugs.

[Lefuneste]

A big thanks Elliott for the information. I'll get some retractable shroud probes from probe master as they really have outstanding quality products.I highly recommend them!! I ordered a probe kit from them last month, and it was very well priced and frankly speaking, the best probes I've ever encountered. I had been searching for top quality probes for a very long time (2 years roughly speaking) without finding any reasonably priced ones. These were a BIG surprise as they are not only superbly built (material, sharpness...), but have a tremendous ergonomics too... A big thank to Dave and to the guy who sent them to the mailbag!!
I intend to use this pretty VOM for mobile phone debugging, measuring amp consumption on startup, as it seems to be the best way to find out what is going on without opening the device.
Now for the battery step-up conversion, I've looked around on ebay in order to find out what is the current trend in voltage boost modules. From what I see, most modules are based around two different chips, the ubiquitous LM2577 which runs at 50kHz, and a new XL6009 which seems to have a 400kHz switching frequency. I will try this latter one as it may fall outside the meter BW. The ripple out of theses modules seem to be a potential issue though, as it is roughly rated between 40 and 120 mV (Chinese standards). The good news is that we should be on the lower end as the meter probably don't take much current to operate, but we may need to add a filtering stage to get a better ripple figure. With a freshly charged quality 18650 (taken out of my e-cigarette stock), you can get 4.2V, with a discharge plateau between 3.8 and 3.6. It should be plenty enough to provide a primary voltage to be cranked up to 28-30V on the secondary without getting mad ripples out of the Chinese module. http://www.ebay.com/itm/DC-DC-Adjustable-Step-up-boost-Power-Converter-Module-XL6009-Replace-LM2577-/310717070508?pt=LH_DefaultDomain_0&hash=item48582e3cac
The funny thing about all this is that I still don't understand what the VOM is doing of these two batteries (30V and 1.5V) as it should be operating passively... Maybe some diode biasing ?

[WattSekunde]

If you're really into old and very old T&M gear have a look at this site

http://www.historische-messgeraete.de/index.php

Now there's somebody with a real fetish!

As far as I can tell it's only available in German but the pictures are good enough  .

Thank you very much for the link! Brilliant Pictures and I always hear it in my head: "a bobby-dazzler", "a thing of beauty", "a work of art", "a joy forever"... ;-)

[elliott]

The funny thing about all this is that I still don't understand what the VOM is doing of these two batteries (30V and 1.5V) as it should be operating passively... Maybe some diode biasing ?

It is only for resistance measurement, the lower ranges run off the 1.5V, the high ranges run off the 30V. On the APL (and most others) it is just the 100,000X range for the 30V, the NA uses it for 10,000X and 100,000X. Voltage and current measurement are completely passive and if you don't need the high resistance range you only need the 1.5V D cell.

That is the same step-up converter that I got, at that price I won't be heart broken if it doesn't work out. The only thing I'm not sure about is how I'm going to turn it off so the step-up converter it isn't draining the battery. I might just take one of my rough condition rear shells and put in a switch.

[switcher]

Here are some pics of the AVO 8 MK III, not only the best analogue meter ever made, but the best model of AVO 8. From the MK IV onwards, they were value engineered. The model pictured was made in Nov 1965. It always surprises me that later, inferior, models go for so much on ebay.

http://koti.mbnet.fi/~ijl/avo_8_mk3.html

[linux-works]

that looks amazing.

its cool that there is this much interest in the analog meters.  I started collecting a few of this brand or that brand of analog meter (simpson and triplett, for the most part) over the last few years, after leaving them behind for many decades.  I admit they are now more for collection and appreciation than real use, though, in my lab.

[AlphZeta]

Here are some pictures of a Chinese-made MF-10A multimeter (they are still being made). It has a 10uA range and x100K resistance range. The input impedance for DC voltages (1V to 100V) is 100K/V. Can't figure out how to re-size pictures when linking in... anyway, you can take a look at the full teardown here: http://www.kerrywong.com/2014/06/28/mf-10a-analog-multimeter-teardown/

[Lefuneste]

It is only for resistance measurement, the lower ranges run off the 1.5V, the high ranges run off the 30V. On the APL (and most others) it is just the 100,000X range for the 30V, the NA uses it for 10,000X and 100,000X. Voltage and current measurement are completely passive and if you don't need the high resistance range you only need the 1.5V D cell.

That is the same step-up converter that I got, at that price I won't be heart broken if it doesn't work out. The only thing I'm not sure about is how I'm going to turn it off so the step-up converter it isn't draining the battery. I might just take one of my rough condition rear shells and put in a switch.

Thanks Elliott for the excellent information. As I said I only intend to use it for voltage and current measurements, so I'll be fine without batteries. Still I will be looking forward after our "little experiment" !!   

[elliott]

Thanks Elliott for the excellent information. As I said I only intend to use it for voltage and current measurements, so I'll be fine without batteries. Still I will be looking forward after our "little experiment" !!   

I don't use mine for resistance measurement often, I have DMMs and an LCR meter better suited to that, but they are great for checking for jitter in old potentiometers. The 1000X range will work well for up to 50K, 100K if you check them in two parts. Of course you could just connect the pot to a power supply and watch the voltage on the wiper.

The 1X range is good for checking intermittent faults in cables, less maddening than listening to a DMM continuity tone for extended periods of time.

[ivaylo]

There were some completely different looking Unigors, these black ones
Judging by the looks and the model numbers (1, 2, 3, 4,...) they must be older than the A43 or the 6e, but no idea how old. Remember salivating after them in 70s in the wrong part of Europe...

[MJR]

You call that a multimeter? NOW this is a multimeter! Straight from 1958. Capable of testing your ICBM launch circuits or getting your damaged B-52 bomb doors back in the game!

The TS-505D/U Electronic Multimeter.

Trouble with your TS-505D? No worries! There is a schematic inside the gas and moisture sealed case. And the technical manual has a nice fold out centerfold of Ms. Schematic 1958. WOW! What a gal.

Wait! TUBES? Yup. None of that silly solid-state stuff here. Well, except for those sexy old-time resistors, that is.

... and yes, I do believe that was  nice wiff of 1958 I detected when I opened the case....

Enjoy!

[mattinx]

Loved the meter teardown, and felt inspired to share photos of my AVO Model 8 - it's clearly Mk II era, although there's nothing to identify it as a Mk II unit. The back panel identifies it as a High Sensitivity unit, and when compared to the Mk II manual, the settings for using the optional external resistance unit (for extended high and low range measurement) are missing - you can see the empty markings either side of the Ohms ranges.

Still has the original probes in the case, although I use newer ones instead This thing is really built like a tank.

I cracked it open and snapped a few photos for you fine folks to peruse - it's another former RAF panclimatic unit, and much like the Model 7 G7PSK posted earlier - you can see the O-ring to seal the unit and the panclimatic markings on some of the resistors.

More photos (including the hires originals) at http://pkl.net/~matt/photos/AVO/

[tzok]

This is not exactly a teardown, but just a gallery of a bunch of Polish analog and digital multimeters produced since 1960-1990:
http://multimetry.tzok.eu/

One of my favorite meters from this collection is UM-110. It's a meter from late '70s/early '80s. This obviously is an electronic multimeter - it has an opamp at the input, and voltmeter input resistance of 10MOhm. What is unique for it is a ohmmeter solution. It works in the opposite way than usual analog ohmmeter, there is an 'infinity Ohm' knob, instead of '0 Ohm'. Please take a look at my video (sorry for a poor quality):


Another great meter from this collection is a V640 made by Meratronik, it was also sold as a Conway Masteranger model 639 and Marconi TF2650. It's unique features are input resistance of 100MOhm and an effective bandwidth of 100kHz (documentation claims 20kHz, but most units were fine up to 80-100kHz) WITHOUT using a dedicated active HF probe (up to 1GHz).

[atkelar]

Very old thread, I know... 
...but it seems nobody has mentioned it so far either on YouTube or here so I made an account to bring it to attention:

Those A43s were aparently very populare with technical schools even in the early 90s. It was basically lab equipment 101 for all new students to learn about the volts, amps and ohms. Since I could not afford anything remotely like that, this was the first real multimeter I had my hands on and I am very sure lots of other people have similar nostalgic feelings about it.

Seeing it on that particular mailbag episode and finally having a model number to go by, I found a reasonably priced one on ebay - it did come with a "scratched in" marker that it did also belong to a school of sorts, so it clearly has seen some abuse, but it seems to do very well still. The wiper contacts might need some cleaning but at several decades everyone needs a scrubbing