In article ,
Paul wrote:
That's a dual op amp which seems to take high rails
voltage and is intended for driving 600 ohm or 2K ohm loads.
The 600 ohm value, I gather, was a telephony headphone
value of long ago (suited to the vacuum tube era perhaps).
I might have had such a headphone at home when I was a kid.

It's the output impedance of a cathode follower valve. The lowest
impendence then without using a transformer.

--
*Why can't women put on mascara with their mouth closed?

Dave Plowman London SW
To e-mail, change noise into sound.