Pearls of the Past (Only for the Voltaically Inclined)

[quantumvolt]

I guess my real entry into obsession (I will never be really hooked) starts here:



I found 2 pcs. on fleabay       

What it is?
If you don't already know, you probably don't care.

[quantumvolt]

Well - I find little or no info about it, and it doesn't look exactly as I would have thought. But it is supposed to be an original HP part:

1820-0001 AMP, REFERENCE

(I believe it - but I am willing to be wrong just for the fun of waiting for these two sexy toys to arrive from America).

If it was just another regulator it should not be stamped C&A ... Here is my guess (I like the drawing, so I borrow it from Russia):

[fmaimon]

Probably a Fluke part. Used on their DC standards, like the 731A, 731B, etc. While it was made by Motorola, it was called SZA263, now it is called LTFLU-1, as it is made by Linear Technology for Fluke.

http://translate.google.com/translate?hl=en&sl=auto&tl=en&u=http%3A%2F%2Fwww.eefocus.com%2Flymexbg2vo%2Fblog%2F10-01%2F183124_69352.html

[quantumvolt]

And if I am right, I can build me a DIY http://www.ko4bb.com/Manuals/Fluke/Misc/732A_Users_Manual.pdf - see Fig. 8-5a, Sheet 2 of 3.

And if I am wrong, never mind. Well worth the gamble ...

[quantumvolt]

Probably a Fluke part. Used on their DC standards, like the 731A, 731B, etc. While it was made by Motorola, it was called SZA263, now it is called LTFLU-1, as it is made by Linear Technology for Fluke.

http://translate.google.com/translate?hl=en&sl=auto&tl=en&u=http%3A%2F%2Fwww.eefocus.com%2Flymexbg2vo%2Fblog%2F10-01%2F183124_69352.html

Hah - you beat me by seconds, and destroyed my dramatic opening 

I hope we are right. Thanks for supporting my game ...

[quantumvolt]

  Ramp Reference  QCR1  1820-0001  transistor&diode   Mot  [orola]

---

Designed of the HP 3440A started about 1961 and HP sold it
until about 197?.

HP will build and ship more than 10,000 HP 3440A digital
voltmeters in only five years.

The electronics of the 3440A are designed by Chuck Near and Dave
Cochran.  Chuck Near was fresh from MSU Engineering school when
he worked on the 3440A design.

The HP 3440A  Digital Volt Meter has a full scale of 10,000
counts with a 5% over-range.   It has a digital output and a
digital control input - neither are IEEE-488.

The HP 3440A was HP's 2nd DVM.  The first HP DVM was the
model 405  which was all tube.

Source: http://www.pa.msu.edu/~edmunds/DVM_HP_3440a/dvm_notes.txt

[quantumvolt]

DESIGN APPROACH
The Model 3440A Digital Volt
meter uses a voltage-to-time-interval
conversion system as outlined in
Fig. 3. The time interval is evalu
ated by digital counter techniques
to obtain the digital display.
The unknown voltage, appropri
ately attenuated, is applied to a
comparator to which a linearly-de
creasing ramp is also applied. When
the ramp voltage becomes equal to
the unknown voltage, a coincidence
pulse is generated, as shown by the
timing diagram in Fig. 5. The ramp
voltage is also applied to a zero
reference comparator which has sig
nal ground for its other input.
Again, when the ramp voltage be
comes equal to signal ground, a
coincidence pulse is generated by
this comparator. The time differ
ence between these two pulses is a
direct analog of the difference be
tween the unknown signal voltage
and signal ground.
The time difference is converted
to digital form by the counting of
clock pulses. The first-occurring
comparator coincidence pulse opens
a count gate, enabling the counters
to operate, and the second pulse
closes the gate to terminate the
count. The first comparator pulse
also starts a Colpitts oscillator
which provides the clock pulses.
By appropriate choice of ramp
slope (400 v/sec) and clock pulse
repetition rate (400 kc) the total
count displayed corresponds to in
put millivolts. Range switching
operates an input attenuator and
places the decimal point so that the
display reads directly in volts.

Source: http://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1963-11.pdf p.3

[sync]

It's maybe used in the 3450A too. Unfortunately there is no part number in the service manual. To make it good it's temperature controlled by a petier element. A LM399 is probably better.

[quantumvolt]

Thank you very much for the beautiful nostalgic schematic.

"An LM399 is probably better"? Yes, sure.

[Edit all]
If I eat noodles for a month, I can buy a legion of LM399 today. The two devices I have found in the fleabay bush of Texas, USA are analog collectables. They are unnused original spare parts produced by Motorola and bought/packed by HP sometime in the 1960s/early70s. So we are talking about 40 years old RefAmps. In the mail list they are classified as 'unobtanium'.

I really like the schematic. It is built like a classic power supply with constant current through the temp compensated ref diode and a precision diff amp for gain. Typical HP quality "engineer" design. Could you please give a link to the manual.

---
[Notes for my next search  MHQ2221 MHQ2229   4JX19A519, 4JX19A555]

[sync]

You can get the 3450B manual from http://cp.literature.agilent.com/litweb/pdf/03450-90007.pdf. Regarding collectibles. I got the whole thing.

[c4757p]

Ooh, wow, that is one good-looking multimeter.

[calexanian]

How many of those did it take to get us to the moon?

[SeanB]

11..........

[calexanian]

My guess is that they hand matched the transistor and the zener, soldered them together, and molded a case around them with those nifty looking gold plated pins sticking out. Hmmmmmm.......  Oh yeah, we call that value added today! Thought that sounded familiar. Hand matched 2n5551 with a collector resistor and ratio metric bias set and emitter transistor. Overmold it in black plastic, and, Bingo! 150 volt amplifier module! Ready to be marked up %1000 and sold as a special selected front end amplifier for all your snooty needs! hahahahaha. It would be funny if it did not really happen!

[mamalala]

My guess is that they hand matched the transistor and the zener, soldered them together, and molded a case around them with those nifty looking gold plated pins sticking out. Hmmmmmm.......  Oh yeah, we call that value added today! Thought that sounded familiar. Hand matched 2n5551 with a collector resistor and ratio metric bias set and emitter transistor. Overmold it in black plastic, and, Bingo! 150 volt amplifier module! Ready to be marked up %1000 and sold as a special selected front end amplifier for all your snooty needs! hahahahaha. It would be funny if it did not really happen!

You do understand that this is not about simply sticking a bunch of parts in a 5$ multimeter an select them by what the display says, right? You do, i hope, at least have an idea that simply selecting a manufacturer and part, that shows the desired parameters over time, is a time consuming task? And that, after a small range of different parts is chosen, evaluating them further requires even more time and folks working on that? Not to mention the resources required to do aging tests. After all, you want to make sure that a part is within specs for, say, 10 years. Do you have any idea what is involved to check for that in just, say, one year?

And finally, i hope that you are aware that precission instruments have rather low sales numbers, compared to the 5$ multimeter you probably would use to select parts? That means that all the time, money and resources spent on these things have to be paid by far, far fewer customers, compared to mass-market devices.

Greetings,

Chris

[calexanian]

My comments are in jest...... One of my jobs involves Mill-PERF testing and I have great sympathy for the engineers of that time period. This company also makes occasionally EA53 tubes. Look that one up and see what it was used for! If I ever have to get them qualified again to make that one I am gonna take out extra life insurance!

[Six_Shooter]

You can get the 3450B manual from http://cp.literature.agilent.com/litweb/pdf/03450-90007.pdf. Regarding collectibles. I got the whole thing.

Excuse me while I change my pants...

One day I will own some bench gear porn like this. 

[quantumvolt]

Yes - a fine instrument.

Anyone has studied the temperature sensing and regulation of the Fluke 732A? There are several thermistors - batteries, oven, front panel (room temp?) - and one more (?) that I cannot find. The schematics are here http://www.ko4bb.com/Manuals/Fluke/Misc/732A_Users_Manual.pdf pp. 93-113.

In this detail - why is base and emitter of Q5 shorted?

[SeanB]

Reverse bias protection for U2. Prevents reverse voltage on the BE junction from getting high enough to zener the junction, which will degrade it with time.

[quantumvolt]

Reverse bias protection for U2. Prevents reverse voltage on the BE junction from getting high enough to zener the junction, which will degrade it with time.

Thanks. So if I understand - the normally reverse biased BC junction of Q5 will shunt the BE junction of U2 in case the latter becomes reverse biased. If so, it has nothing to do with temperature compensation?

[SeanB]

Just a very cheap and very low leakage diode. The reverse leakage is so small that it will have no affect on the reference bias up to temperatures where the solder on the devices melt. It protects the reference during power up and power down if the rails decay at different rates, or if a supply rail fails in operation.

[quantumvolt]

Thanks. Anyone familiar with the rest of the large advanced analog ref schematic, and want to share their knowledge/skills in the form of pointing out what is absolutely necessary for a small DIY ref board with the transistor+diode part?

[david77]

You can get the 3450B manual from http://cp.literature.agilent.com/litweb/pdf/03450-90007.pdf. Regarding collectibles. I got the whole thing.

Sorry for the OT:

Is that the one that was on ebay.de a few weeks ago? I was very much tempted to get it myself, took a lot of self control  .
Could you let us have a sneaky peek inside, please?

[sync]

Is that the one that was on ebay.de a few weeks ago? I was very much tempted to get it myself, took a lot of self control  .
Could you let us have a sneaky peek inside, please?

Yes, it's the one from ebay.de. I only have a phone as camera. Taking acceptable pictures is a pain. Here is a teardown (not from me): http://www.josvandijken.nl/elektronica_Hewlett-Packard_3450A.php

[mamalala]

Is that the one that was on ebay.de a few weeks ago? I was very much tempted to get it myself, took a lot of self control  .
Could you let us have a sneaky peek inside, please?

Yes, it's the one from ebay.de. I only have a phone as camera. Taking acceptable pictures is a pain. Here is a teardown (not from me): http://www.josvandijken.nl/elektronica_Hewlett-Packard_3450A.php

What a nice machine. I'm wondering if it was some kind of standard back then to build stuff in such a modular fashion? I have a Fluke 8502A, which is also full of plugin-modules for pretty much all of it's functions, and it dates to the 70's and 80's.

Greetings,

Chris