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2MHz True RMS Millivoltmeter Circuit – Equivalents to Russian Devices shown?

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Chris56000:
Hi!

Can anyone advise me on suitable equivalents for the Russian transistors, operational amplifiers and transistor arrays in the schematic for this Wide Band True RMS Millivoltmeter please?

http://irls.narod.ru/izm/volt/skv.htm

For example, many "equivalents" commonly quoted on websites are nonsense without a redesign, the K140UD16 has an equivalent quoted as "LM741CH", but the K140UD16 has it's Null Balance pins connected to the positive supply, indicating the pins are connected to the collectors of the input stage transistors, and some other opamps shown have frequency compensation capacitors, again, the 741 quoted as "equivalent" is nonsense, because the author points out in the circuit notes the opamps with a wide gain–bandwidth product are needed!

I'm aware that a lot of these Russian devices are "flat–pack" or metal can type and I'm happy with modifying the chap's suggested PCB layouts to suit Western equivalent devices!

Can anyone point me in the direction of a Russian Op amp databook?

Chris Williams

ch_scr:
I've been looking at / for russian datasheets as well, what I've learned so far is:
- use a russian search engine (e.g. yandex.com)
- use a browser that can translate whole websites "on the fly" (like Chrome)
- search the name with russian letters "к140уд16" instead of western "K140UD16"
K140ud16 seems to be an uncommon one, I've attached the datasheet that has turned up with the method described above.

Interesting note: In the circuit diagram above, it says "A6-A8, A9 K140UD11" but a bit below it says "A9 K140UD16".
I've also seen example circuits in datasheets where e.g. power or ground connections were missing.
When I told an old TV repair hand (from east germany), he replied along the lines of "Yeah the circuit diagrams were known to be slightly off".
Good luck!

Edit: Here is the initial text from the datasheet, raw google translate, seems the "Analogy list" is not too far off after all?

--- Quote ---GENERAL DESCRIPTION
Integrated circuits 140UD7, 140UD16, 140UD20, KR1005UD1
are general purpose operational amplifiers with internal
frequency correction. The amplifiers are made according to a
scheme close to џА741.
The circuit diagram of the op-amp 140UD7 differs from
the џA741 circuit mainly in the device of the output stage.
In addition, there is an additional output from the
input of the amplifying stage for connecting a correction
capacitor. Connecting an external capacitor between
this pin and the inverting input increases the output
voltage slew rate to 10 V/µs when inverting.

140UD16 is an export version of 140UD7

KR1005UD1 - two op-amps 140UD7 (without correction output),
located in one housing with a single-row arrangement of pins.

140UD20, two op-amps 140UD7 (without correction output),
located in one housing with a two-row arrangement of pins.

KR140UD20AM - two op amps located on one chip.
Their circuits differ from the 140UD7 circuit in the output stage and
the presence of input stage base current compensation nodes,
ue to which the input current is an order of magnitude
less than that of the 140UD7.
--- End quote ---

dobsonr741:
You can be dead in the water without 19VNT1B matched transistor array. Even more, we don’t know what the Russian yield of this design was. They did electronics “at all costs”.

The claimed 2MHz 1% accuracy for sine wave is difficult to believe, for both the full wave rectifier and the log-antilog converter will have less than 10KHz -3dB bandwidth, just by the look of it. Compare this schematics with the best in class, still-in-production AD637: claims only 200KHz bandwidth for 1% error. And that is for a monolithic, laser trimmed rms converter.

If you aim to recreate an analog true rms meter, the best bet is AD8361, with a VGA servo operating it in a fixed output voltage setting. It can operate down to 20Hz, surprising from a 2.5GHz detector.

Chris56000:
Member Ch–Scr, thank you for your time and tips sir!


I do use Chrome that translates "on the fly", and from what I can make out from the datasheet, which is an image and not OCR'd, the "к140уд16" has the Null Balance pins connected to the diff. stage transistor emitters, so the circuit published isn't correct, unless the original author of the project found it worked by returning the null preset slider to the positive line with higher resistor values!

Chris Williams

ch_scr:
While translate.google.com doesn't like the pdf, one can make a screenshot and feed the picture into it. There even is a button to get "just the text" back.
Please report back when you find a better way  |O

The offset compensation shown in "к140уд16" datasheet is also connected to negative voltage.
Would the circuit in the original post work for the "к140уд11"?
One has to consider all this was drawn by hand, and at a time when photocopiers were but an engineers dream.
So one might speculate, that it was found the circuit worked better with A9 replaced by "к140уд16" and an additional note was made -
but a rework of the whole schematic was deemed too laborious.
Also just because the offset compensation was drawn and prepared for in the layout doesn't mean it would have to be populated -
maybe it was found to be unnecessary and the parts were just left out anyway?

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