-83

[zhtoor]

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[Kleinstein]

It looks like the µA728 might be an early buried zener, maybe the the first. It looks like it got replaced by the LM399 for most part and was not used very much.

Different from the LTZ1000 / LM399 the zener and diode part are stilt with a diode connected transistor and not using a ref amp, with the transistor used as the first stage of amplification.

The concept of having two current sources and thus a nearly floating reference has some interesting aspects, however it also means a relatively high power dissipation in the chip, which is not a good start for temperature regulated chip.

[Kleinstein]

It might be a product that had problems, like with the cases or with a special process needed to make the zener. Patent problems are another possible reason for not selling a product.

With such old, special parts data-sheets are sometimes rare. It may not even made it to the normal marked.

[Gyro]

uA726 was a dual matched transistor with a heater on-board, datasheet public, fairly popular (maybe even available today).

Obviously used a lot in Synths...

http://www.ebay.co.uk/itm/Fairchild-UA726HC-VINTAGE-SYNTH-MiniMoog-Roland-System-100-SH-1-Korg-Trident-/322548545231?hash=item4b196436cf:g:2tIAAOSw-3FZK8pI