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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Oct Thu 25, 2018 5:46 pm 
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Restoration is a must, considering that there are fewer of these edge display/stepper meters existing than nearly any other type of old electronic test equipment that I can think of. They are also among the most intriguing pieces of vintage gear considering the looks of the displays and sound of their operation, plus the technology they employed. Putting them in museums where no one would ever run them wouldn’t do these things justice.

-Mark-

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Wed 16, 2019 1:29 am 
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Location: East Falmouth, MA
When I was in high School in San Diego (in the late 50's), where I grew up, I entered projects in the Science Fair. One nifty fallout of this was that I became acquainted with some of the area engineers, became a student member of the local ISA chapter, and through that set of contacts, was given "old" gear to experiment with by some of the members and member companies. This included Electro Instruments, which was in it's heyday at the time. I received a bunch of parts to use and gear to cannabalize, and also some working gear. In addition to operational amplifiers (I only received parts of these), they made X-Y plotters (I had one of those and it is long gone, but I still have the servo motors and pots) and the digital voltmeters discussed in this topic. I still have the DVM's and some parts.

I have two DVM's: one has no model number on it, but I believe it to be a model 4500. It is a big rack-mount beast, similar to the one that Cubdriver posted a photo of. Mine is a bit different - it is two parts. The big part is the same size as Cubdriver's, and contains the power supply, steppers, control electronics, but no display. The second, a 2U rack unit, has the display and an AC converter plus a power supply for the converter. The two parts are connected with two cables with 50 pin D style connectors. One cable connects the display to the steppers; the other is control signals and power. The voltmeter is autoranging for DC, but has manual range switching for AC (because of the converter): 10V, 100V, 1000V AC ranges. This unit worked when I last plugged it in but that was at least 30 years ago. It has a liquid standard cell reference. More importantly for this topic, I have the original instruction manual for it and the manual contains full schematics along with a detailed "how it works" section, plus repair info and calibration procedures. At this point, I wouldn't plug it in without changing out all the can caps and at least testing the other caps first.

I also have what I think is a Model R-40; it has a label but the label is now hard to read. It is a portable model and looks like the one that Mark Palmer restored. It measures DC voltage only and is autoranging. It has the zener reference in the Bulova oven. I am quite certain that the oven contains a zener and not a crystal - there is no crystal used in the Model 4500 - the stepper pulses derive from the 60Hz line frequency - and I don't think that scheme was changed when the zener reference became commercially viable. This unit also worked well when last used many years ago; for quite a while it was my go-to DVM until solid-state units became affordable. I remember that it took quite a while to warm up and stabilize; probably due to the time for the zener oven to stabilize. Once warmed up, it was very stable. Some of the shock mounts for the steppers have disintegrated leaving the steppers hanging, but luckily, among the parts I received and still have is a handful of spare shock mounts which appear to have some life left in them. One of the black beauty caps has a big crack in the plastic and I'm sure that all the can caps need to be replaced before trying to fire the meter up. Both units still have the original noise reduction foam which is very dead and crumbly and should be cleaned out before anyone tries to run them. Some years ago, there was another discussion of the edge displays, I think on this forum, and Alan Douglas posted that he knew a guy who had one of the meters with the edge display. I'm that guy and this is that meter which I was using at work when we both worked at Benthos many years ago.

I recall being told that the precision resistors used in the stepper driven potentiometer were custom wirewound high precision resistors that Electro Instruments made in-house. I have a few of those in my parts collection. The resistors were the key to the precision of the meter.

I always thought the stacked lucite display was pretty neat - I once cannabalized a large DVM model and made a digital clock using the display and steppers. It worked OK for a while, and made a nice satisfying thunk once per second, and an even bigger sound each time a decade turned over. The sound was particularly grand when several digits advanced to zero together.

I have some extra display modules in my collection - a couple of 5 "digit" ones and a couple of 6 "digit" ones. I say "digit" because one "digit" space is used for symbols. The symbols in some of them include the Greek letter for ohm, so they must have made digital ohmmeters also.

They also gave me a calibration box - it contains a set of Epply liquid standard cells wired in series and with a bunch of binding posts on the front panel so you could get various multiples of the standard cell voltage (1.0193v), so you could check not only the high end of the range, but the linearity withing the range. A few years ago, I cleaned out all the dead foam - the whole box was stuffed with foam, I think for temperature stabilization plus shock mounting, and found that the cells were still OK. The Epply standard cells don't like being shaken up and like to be in a stable environment and do not supply much current - best to measure them with a very high input R meter. This is one reason why the design of the DVM's was an automated potentiometer scheme - at balance there was very little current drain from the reference.

I have quite a few photos of them, inside and outside. I'd post photos but I have to figure out how to reduce the photo file size to meet the attachment size limit.

I'm never going to get around to restoring these DVM's. If any of you are interested, please PM me.

Clyde Tyndale
Falmouth, MA


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Wed 16, 2019 4:51 pm 
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Thank you for the story Clyde, and for more insight on EI and their products as there is so little information out there on this company despite the fact that they were highly successful. As I'm discovering from others EI made a lot of strange beasts, many of which were customized meters for the USAF.

I was happy to receive the Mark IV meter I have in as good of condition as it was, a lot of this was due to the fact that it died long ago when those rubber isolators broke and snapped the fuse holder. (New isolators are easy to get today.) I'm honestly surprised no one threw the Mark IV in the trash long ago after this happened. The restoration was a fun and enjoyable project. Without a doubt others here will take you up on your offer. I like to spread the fun around and not hoard so others can work on and learn about these fascinating old devices too. The "paint" tool in Windows is an easy way to downsize images to post using the resize tab. I would love to see the photos of your EI maters!

-Mark-

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Wed 16, 2019 4:58 pm 
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Clyde, I am interested and sent a PM. I will actually be in MA towards the end of the month, perhaps can pick it up.

Barry

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Wed 16, 2019 7:07 pm 
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I posted a YouTube video of the EI Mark IV a few months ago, I don't think I linked it here. Others who are unfamiliar with these things can see and hear the sights and sounds of these goofy things. This style stepper meter must have been a bear to put up with if you had to listen to them all day long. Non Linear Systems came out with much quieter relay switched versions later in the game, but from what I have gathered they were ridiculously expensive.

https://www.youtube.com/watch?v=7hWlwhlLgQ8

-Mark-

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Wed 16, 2019 9:16 pm 
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I designed museum exhibits that sometimes used a stepper or three. Also 24 pole shorting relays and other fun stuff. We had to sound isolate the control systems of course

I wonder what early telephone exchanges sounded like

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 3:52 am 
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Joined: Jan Tue 15, 2019 9:36 pm
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Location: East Falmouth, MA
Mark, I like your video of the Mark IV running. When mine was much younger, and the interior foam was in good condition, I don't remember the sound as being all that loud, and much more muffled sounding than yours. It wasn't bothersome at all in use on my bench at work and most everybody thought it was a neat gadget.

Those DVMs were best at measuring stable voltages. If there was much AC superimposed on a DC voltage (think power supply with hum), it would be hard to get a measurement, especially if the hum was enough to get more than the last digit moving. It was sort of fun to hook the input of the meter to a slow ramp voltage, like a very slow timebase signal from a Tektronix scope. With a very slow ramp input, the meter would count upwards very nicely.

And if anyone wants to hear what an old relay based telephone exchange sounds like, they should check out the Telephone Museum in Ellsworth, Maine. Their collection includes entire exchange switch systems ranging from very early manual/operator plug systems, to the stepping relay (Strowger switch) systems, up to a number 5 crossbar switch and they have managed to get many of them running so you can see and hear them as they process calls. It is a neat museum for telephone and relay geeks. Their website is http://thetelephonemuseum.org/


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 8:45 pm 
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Thanks for the tip on re-sizing photos. Here are some photos of My Model R40 which is similar to the Mark IV. might even be the same as the label on mine is damaged - it could be a R40 Mark IV
Attachment:
File comment: Label on the back of the DVM
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following are two interior views
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and a front panel view
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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 8:59 pm 
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I'm not sure if they changed the model name somewhere along the line, but the meter in your pictures Clyde is totally identical to the one I have posted the restoration of here both inside and out. ;)

Image

Maybe they knew that a guy named Mark would own it someday LOL. It is nice to know there is at least one twin of it around!

-Mark-

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Last edited by MarkPalmer on Jan Thu 17, 2019 9:05 pm, edited 1 time in total.

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 9:01 pm 
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Location: East Falmouth, MA
Two more photos of the R40 - Mark IV
It even has a place to store the power cord.
Attachment:
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Here is a rear view showing the circuit board
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to the left of the transformer and just under the two fuseholders is the Bulova oven which contains the zener reference. The oven plugs into an octal socket. The large black cylinder with the top connector (also plugged into an octal socket ) is the chopper which is used to switch between the reference voltage and the output of the stepper potentiometer. The chopper output is used to drive the stepper potentiometer in the correct direction to approach balance. That's the really short form of how it works.
The green squares are selenium rectifier stacks.


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 9:06 pm 
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Location: East Falmouth, MA
Hi Mark,

Maybe they did. :lol: You must have been destined to own one. It does look like a change along the line sometime. If the serial numbers were sequential, then they changed it from R40 to Mark IV. I wonder if there was some subtle internal revision?


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 9:17 pm 
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Location: East Falmouth, MA
Here are some photos of the Model 4500:

2 exterior views of the entire system:
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Followed by some views of the AC converter / display unit:
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I may have added the power switch for the AC converter.

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Attachment:
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IMG_6685.jpg [ 125.39 KiB | Viewed 1274 times ]


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 9:19 pm 
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Revision 01: Disconnect all the guts, leave them in for show, and wire in a Radio shack DVM :)

who would ever know? 8)

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 9:21 pm 
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Your R-40 looks to be in better shape internally than mine was Clyde. All 6 of my steppers were broken off of their rubber isolators, and it was being ran that way at least until one of them hit the back of the one fuse holder hard enough to break it apart. Along with the 10V Zener inside the Bulova oven, there is another 6.2V "thermally compensated" Zener on the socket of the chopper. I wondered what this 6.2V one did, I couldn't figure it out when I repaired mine.

-Mark-

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 9:24 pm 
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Now that 4500 is A BEAST! Lovely! Very rare to find the pieces together with the interconnecting cables and everything in that great of shape. I hope Barry can have the pleasure to tackle that one ;)

-Mark-

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 9:28 pm 
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Location: East Falmouth, MA
Here are photos of the control unit of the 4500
This view is with the stepper section cover removed. The cover is in place in some of the other photos.
Attachment:
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The cover is in place in this one

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The Epply standard cell reference is behind the black rectangular plate at the lower right of the next photo.
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Here is the unit with all covers in place
Attachment:
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IMG_6694.jpg [ 106.16 KiB | Viewed 1271 times ]


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 9:30 pm 
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That 4500 is a thing of beauty!!

-Pat

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 9:35 pm 
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OK, Mark and Clyde. I am going to have to post some pictures of my EI 8409 DVM from the late 50's
or early 60's. It is all germanium transistors and Nixie tubes so it's operation is quiet.

It is nice to see this old DVM technology and even better to see it still operational.

Pictures in a day or two.

Bob


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 9:39 pm 
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And you posted the follow up pics as I posted my earlier reply. That looks very much like a remote display version of the all in one unit I have!

Image

Mine has a broken wire on one of the stepper relays; it broke free I assume during the shipment of the meter when the relays broke loose and rattled about(it was basically NOT packed - the cardboard was almost literally wrapped around the enclosure). If I dig mine out later and get a photo of the relay and broken wire, would you please look at yours and see if there's a similar wire and where it connects? I haven't found schematics I trust for it.

The rest of the pics are at: https://pmanning.smugmug.com/Electronics/Electro-Instruments-NLS-edge

If you could do so, it would be most helpful!

-Pat

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Thu 17, 2019 9:42 pm 
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Another fellow sent me some pictures of the EI meter he is restoring, a two piece model T121 multimeter made for the USAF. It is a later solid state one but still using edge displays, and it's incredibly complex. I'll ask him for permission to post the photos of it here.

I see the same 6 stepper configuration was fairly commonplace to most of EI's meters. Even though these things are museum pieces so to say, if in museums no one would likely see them run which is what really makes them interesting.

-Mark-

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