Integrated Op Amps - the early days

26 Feb 2022

Great to see a Project14 focused on Op Amps: Op-Amp-a-Palooza.

I don't have time to do a clever and innovative project, but looking forward to see what other members come up with.

It got me to thinking about when I first started out using IC Op Amps back in the early 1970s. First started using the uncompensated 709s and 308s and then quickly moved to the compensated 741s (1MHz was sufficient for most of what I was doing and these were inherently stable, although the early ones from TI were prone to latch-up).

I have a collection of vintage parts (709, 741, 747, 558). I was surprised that I did not have some 308s - probably stashed somewhere else. Back in those days the parts were sometimes hard to get at a reasonable price, so I resorted to buying unmarked and sometimes untested parts and testing them myself. I would use a Sharpie or scribe to mark the parts after I tested them.

Here's a picture of some of my collection:

A range of vendors and styles. Early parts were packaged in metal TO cans or ceramic DIPs (probably still are for military use) and later in plastic packages for cost and ease of manufacturing. The parts here are from Fairchild, TI, Raytheon, Signetics, and National. The earliest date stamps are 6916 for a National LM709 and 7016 for a TI SN72741. The unmarked parts pre-date those.

Those were the wild west days - I remember that we would use Motorola MECL digital ICs and would bias the power supply so we could use them as linear small signal differential amplifiers - the precursor to using these op amps.

If I find some time, I'd like to try some of these out again...

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jc2048 over 3 years ago

The ceramic packages are interesting. Perhaps they were internal engineering samples that escaped to the wild.

The oldest ones I can find are these LM301AN parts with a 1981 date code. I'll try them out and see if they still work. They don't have internal compensation, so perhaps I could try experimenting with compensation techniques, or something like that.
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jc2048 over 3 years ago in reply to jc2048

I've finally gotten around to trying the four that I had. They all work fine. The offset voltages at the input measure +281uV, +28uV, -80uV, and -776uV, so two of them are particularly good (the datasheet gives 2mV typ and 7.5mV max). I was going to try measuring the open-loop gain but that turns out to be quite difficult.
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Jan Cumps over 3 years ago in reply to jc2048

I was going to try measuring the open-loop gain but that turns out to be quite difficult.

I'm reading up on how to do this properly.

Omicron: Operational Amplifier - Open Loop Gain Measurement
Analog Devices: Simple Op Amp Measurements
Venable Instruments: Measuring the Open Loop Gain of an Operational Amplifier

The last one has the simplest requirements on lab instruments: (symmetric) supply, generator and a 2 channel scope.
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Jan Cumps over 3 years ago in reply to Jan Cumps

This is a setup for the 3rd option. I replaced the 100R with 50R to match generator impedance. The 3 other resistors are 1K9 because I have no 1K's left.

The IC is a ST ua741, I have a lot of those
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Jan Cumps over 3 years ago in reply to Jan Cumps

This is a setup for the 3rd option. I replaced the 100R with 50R to match generator impedance. The 3 other resistors are 1K9 because I have no 1K's left.

The IC is a ST ua741, I have a lot of those
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