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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Sat 19, 2019 4:45 am 
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Joined: Jan Tue 15, 2019 9:36 pm
Posts: 37
Location: East Falmouth, MA
Mark -

I think there may be some differences between the R40 and the Mark IV

Here is a closeup of the main circuit board of mine, with the tubes, etc labeled.
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IMG_6766.JPG
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Here is the back side of the board.
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IMG_6744.JPG
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I don't have a zener anywhere visible, but there is a neon tube. Neons were sometimes used as voltage limiters for protection purposes. Neither is in the schematics for the 4500.

Can you see any other differences between the R-40 and the Mark IV?

Some circuit tracing may be in order here. My assumption is that the stepper section is more or less identical between the models, so only the simpler circit board needs to be traced out.

Clyde


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Sat 19, 2019 4:58 am 
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Joined: Jan Tue 15, 2019 9:36 pm
Posts: 37
Location: East Falmouth, MA
I might add that neon tubes were also often used in the old days for level shifting in DC coupled tube based amplifiers. The push-pull driver in the 4500 uses two of them for that purpose. They seem to have simplified the driver amp in the R40 as neither the neons or the intermediate driver tubes are present


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Sat 19, 2019 5:40 am 
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Posts: 3076
Location: Erie, PA
There are couple of slight differences between the Mark IV and the R40. The second Zener in the Mark IV is a Hoffman branded 1N429 6.2 volt at the chopper, and no neon lamp.

Image

This is the Mark IV chassis after I refurbished it. The canned electrolytics were re-stuffed, originals were toast. The 1N429 was temporarily replaced with a NTE5013A here for testing, but the old temp compensated Hoffman turned out to be OK so I put it back in later.

Image

Clyde, I believe those single plane displays you have are the ones Cohu used in their digital meter models. I have never seen one of their meters up close, but was told they used "projection" style displays. Thanks a bunch for sharing all of this here, this is the most and the best EI information I have seen!

-Mark-

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Sat 19, 2019 4:46 pm 
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Joined: Jan Thu 01, 1970 1:00 am
Posts: 188
Location: Colorado Springs, Colorado
Thanks for posting the pictures. Clyde. Those single plane displays sure make
nice crisp characters.

Also, the theory of operation you posted is very similar to my later all transistor meter.
Mine also has the programmable potentiometer. It differs in that it uses transistor
flip flops / counters / registers in place of the stepper relays to count and store the number
of up or down pulses needed to bring the potentiometer into balance with the measured voltage.

Interesting to see the advance in DVM technology was made in small steps as opposed to an entire
departure from the previous design.

Bob


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Tue 22, 2019 6:09 pm 
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Joined: Jan Tue 15, 2019 9:36 pm
Posts: 37
Location: East Falmouth, MA
I've done some circuit tracing on my R40. Here is the schematic for the power supply and the amplifier. Hopefully, I have transcribed it accurately.
Attachment:
EI R40 Scematic PS & AMP.pdf [171.28 KiB]
Downloaded 59 times


Two differences with Mark's later unit are obvious:
The NE-2 mounted on the chopper socket in my unit has been replaced with a zener in his unit
one of the blue wirewound resistors in mine has been deleted in his unit.

note that unused pins on the chopper and oven sockets are sometimes used as a tie point for unrelated connections.

Looking at the diagram, it is apparent that the NE-2 or zener mounted on the chopper socket is not used as a reference. It appears to be a voltage limiter for the amplifier input.

I did some measurements on the oven which are reflected in the schematic. The zener appears to be two zeners back to back as it clamps at about 12 v in either polarity. Also the oven has a series capacitor in the heater coil circuit. Something that looks like a ceramic disc is visible when I open the unit and my Z meter measures it as a capacitor.

Someone commented about the resistors on the steppers. I recall being told that EI made their precision resistors in house as their accuracy was critical for the high performance of the DVM. They are wirewound resistors. For the "jellybean" resistors found in the stepper section, the value is 1 ohm times 10 to the exponent indicated by the body color according to the standard color code. Black = 1 ohm, brown = 10 ohm, etc. This color scheme applies to the barrel shaped ones also. All the resistors with a tan color have various values and the values should be written on them. Sometimes the barrel ones have a value written on them regardless of the body color.

The delay relay is used to delay the application of power to the stepper driver thyatrons until all the other tubes are warmed up.

note that the oven is always on whenever the power is plugged in, which should reduce reference stabilization time for the meter.


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Tue 22, 2019 6:12 pm 
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Joined: Jan Tue 15, 2019 9:36 pm
Posts: 37
Location: East Falmouth, MA
It is the 50 ohm 5 watt resistor that appears to have been deleted in the later model.

clyde


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Mon 28, 2019 8:01 am 
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Posts: 395
Location: Southeastern Litchfield County, CT
I've been picking away at the old tattered beast I have over the past week or so. The can caps all seem to have re-formed acceptably after spending some time on a current-limited 320V power supply; all had leakages ending in the sub miliamp range which is below what is called out as acceptable in the formula in the Sprague TO-6 manual I have:

I=kC + 0.3

I= leakage in mA; k= constant, 0.025 for 250-350WV caps; C = cap in uF

This would result in maximum 1.3mA 'new' leakage for the 40uF, 350V caps in the unit; they were all below 1mA and looked good value and loss-wise on an HP 4262A LCR meter.

I've begun reverse engineering the voltage reference board as it uses the standard cell and the one in the manual I have shows a zener reference and is completely different. Thankfully it's a single-sided board, so it shouldn't be too bad. I only just started that tonight, and so haven't gotten too far.

Image

Image

Image

Image

-Pat

Edit to add - other photos have been added to the instrument's gallery: https://pmanning.smugmug.com/Electronics/Electro-Instruments-NLS-edge

Edit again to add - I just noticed I fouled up the connection diagram for the top left can electrolytic - the green wires should go to the half-round cap terminal, not the nearby can lug. D'oh!

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Mon 28, 2019 3:32 pm 
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Joined: May Mon 18, 2009 5:55 pm
Posts: 3076
Location: Erie, PA
Thanks for the professional schematic of the R40 amplifier circuit Clyde, that must have consumed a lot of time. Your excellent work is very much appreciated. Down the road, I'm sure others who come across this old equipment will also appreciate the time you and Cubdriver are putting in to tracing these things out. I imagine all the original EI service data went to Honeywell when they bought the company, and it was more than likely all tossed in a dumpster at some point when it was deemed no longer necessary.

-Mark-

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Jan Mon 28, 2019 7:02 pm 
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Joined: Jan Tue 15, 2019 9:36 pm
Posts: 37
Location: East Falmouth, MA
Mark,

you are welcome. Drawing the circuit was a bit of a mind trip - it's been a very long time since I've drawn a schematic with tubes in it, long before I started using AutoCAD.

Fortunately a complete manual for the 4500 wound up in my files. Member K7MCG has been helping me with stitching together photos and scans of the original, somewhat faded, C size schematics. I've also copied them into AutoCAD. It was a lot faster to make drawings from other drawings as opposed to circuit tracing. I'm happy to make the manual available. The text pages of the manual have been scanned into a pdf file.

At present, the in-progress manual is in a DropBox folder. Does the forum have a place to upload things like the manual? The files will probably be too large to include in a post.

Clyde


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Feb Sat 09, 2019 7:58 pm 
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Joined: Jan Tue 15, 2019 9:36 pm
Posts: 37
Location: East Falmouth, MA
Digging through some papers I found the following business card. While I can't say I remember Rhett after all of these years, if I have his card, he must have been one of those who were responsible for my having the EI gear.

Attachment:
Business Card side 1.jpg
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Business Card side 2.jpg
Business Card side 2.jpg [ 130.95 KiB | Viewed 957 times ]


It is a fold-over card; hence what seems like an odd size. The list of products they made at the time is interesting, and they had converted to transistorized models by the time he gave me the card. Don't recall when that was, but it had to be before June 1964 when I moved east.

I did a bit of research and found his obit:

Board:
Message Boards > Surnames > Rathbone
URL:
https://www.ancestry.co.uk/boards/surna ... 85/mb.ashx
Subject: Obit. R. Rhett Rathbone
Author: kayrom63
Date: 02 April 2004
Classification: Obituary
Surnames:

May 15, 1931-March 26, 2003

R. Rhett Rathbone, 71, of San Diego died March 26. He was born in Detroit and was an electronics metrologist. He was a member of the First Unitarian Universalist Church and the Zoological Society of San Diego. Survivors include his wife, Alice; daughter, Wendy of Yucca Valley; son, Andy of San Diego; and brothers, Frank of San Diego, Peter of Carlsbad and Jack of Cumberland, Md. Private services were held.
Donations: First Unitarian Universalist Church, 4190 Front St., San Diego, CA 92103, or charity of choice. Arrangements: Mayer Mortuary. Published in the San Diego Union-Tribune on 4/5/2003. (volunteer submission)



My thanks to Rhett and the others who helped a young kid with his interest in electronics all those years ago.


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Feb Sat 09, 2019 8:06 pm 
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Joined: Jan Tue 15, 2019 9:36 pm
Posts: 37
Location: East Falmouth, MA
A quick google search turns up that 3540 Aero Court, Rhett's office, and possibly the home of EI at that time, is now SET High, the School for Entrepreneurship & Technology, a charter high school.


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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Feb Sun 10, 2019 2:35 am 
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Joined: May Mon 18, 2009 5:55 pm
Posts: 3076
Location: Erie, PA
Thanks for sharing the business card Clyde, what an interesting find! I believe '65 was the last year for EI in San Diego, being bought out by Honeywell who had a test instrument division in Denver, CO. They continued some of the last EI meter models as re-badged as "Honeywell EI," but I think their main interest in buying EI was for the chart recorders, my guess was to eliminate them as competition.

-Mark-

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 Post subject: Re: Edge display/stepper voltmeter crystal frequency referen
PostPosted: Sep Sun 26, 2021 4:44 am 
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Joined: Sep Fri 10, 2010 3:31 am
Posts: 34
Location: San Diego, CA
Steve Johnson wrote:
Unfortunately I have never seen any NLS schematics for these. I have the first two hardcover theory books published by NLS but they are theory and don't contain any circuit schematics.
Image


Hi Steve. I know this is an old thread but had some information you might be interested in. Surplus Sales of Nebraska has the NLS 481 manual available for purchase. Link is here: https://www.surplussales.com/Manuals/ma ... _test.html .

The reason I know this is that I actually picked up a NLS 481 a couple of weeks ago and got the manual (Surplus Sales makes a copy of the one they have and it has a very nice schematic along with a theory of operation and troubleshooting info). My unit is missing the the removable display but I have some options for recreating it or maybe someone has a display that they will be willing to sell. Hope this helps.

73, Gordon KJ6IKT


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