Fluke 8125A military DMM teardown

[bluey]

Found this big list of model numbers and short descriptions.

https://www.davmar.org/temodel.html#fluke

Radiomuseum doesn’t have an 8125a yet!
https://www.radiomuseum.org/m/fluke_usa_en_1.html

[tggzzz]

I might as well put the 12 page "TB 9-4935-365-35" military calibration manual here, for posterity.

No, I can't remember where I got them from.

[bluey]

8100a manual is here - might be close


http://www.nixiebunny.com/fluke8100b/fluke8100b.html

[bluey]

Fluke 8120a manual is here
https://www.eevblog.com/forum/testgear/fluke-8110a-8120a-nixie-dmm/msg1001781/#msg1001781

[bluey]

Fluke 1974 catalog includes 8125A. $1995 or with battery $2195!
http://doc.xdevs.com/doc/Fluke/Fluke_Catalog_1974.pdf

[picburner]

There is one for sale here but the lid is missing.

[tggzzz]

I suspect the mains lead is also missing, in the lid. The connector is non standard.

[tooki]

I suspect the mains lead is also missing, in the lid. The connector is non standard.

Nonstandard as in non-IEC, you mean? The connector itself is practically guaranteed to be a standard military circular connector. Easy enough to order, but very, very rough on the wallet...

[tggzzz]

Well, I sold it.

It was only taking up space in the garage, and I've got another Fluke DVM with nixies, so I preferred that someone else would "cherish it". A nice chap at bought it at a hamfest over the weekend.

Now that it has gone, of course I regret it. It was  a peculiar device, and my remaining nixie DVM is nowhere near as quirky.

[MegaVolt]

What is the reference voltage source in it?

[tggzzz]

The manual says only that Q11, R15, R22 are ordered as a matched set.

[TimFox]

The old "reference amplifier" (Q11) chips were individually characterized by Fluke for the appropriate current that gave zero tempco. 
Resistor R15 sets the current, and resistor R22 gives a gross adjustment for the output voltage of the amplifier.

[MegaVolt]

The manual says only that Q11, R15, R22 are ordered as a matched set.

I have seen the diagram. This is very similar to SZA263. But maybe they used a different zener. Is its name visible in the device? Perhaps there is a photo?

[alm]

Fluke used the TI DH80417A refamp before the SZA263 in calibrators, voltage references (731A and early 731B) and multimeters (8800?) in the seventies. So that would be my guess.

[tggzzz]

The manual says only that Q11, R15, R22 are ordered as a matched set.

I have seen the diagram. This is very similar to SZA263. But maybe they used a different zener. Is its name visible in the device? Perhaps there is a photo?

I've sold the DVM, so the only photos are in this thread.

[alm]

If the TO-39 IC in the attached crop from one of tggzzz's pictures is indeed the voltage reference, then it might be indeed the DH80417A or DH80417B refamp. The picture is too low resolution to tell for sure, but it seems to have a logo on top and marking on the side, like in the pictures here and here (look for 731A pictures).

[Dr. Frank]

Reference Amplifier DH80417B from my old 332B/AF:
https://www.eevblog.com/forum/testgear/fluke-332baf-in-the-slaughterhouse/msg393627/#msg393627

This marking is different, and not centered on top. The component seems to be from Siemens, that's what the logo looks alike.
A bigger capital S and a smaller capital H, for Siemens & Halske. That logo was used on the TCA365 also, and Siemens made OpAmps in the seventies, afair.
It's better visible, when you download the jpg and zoom in.


Frank