Arny Krueger wrote:

The sort of vacuum tube op amps I'm thinking of were more on
the order of this one:

http://ed-thelen.org/dc_amp.gif

Man, that thing has a HUGE number of tubes in it!

There's really no excuse for vacuum tube amplifiers to be
terribly slow, after all Tektronics made some pretty fast
'scopes out of bottles....

There is indeed: remember that you can either have gain or you can
have bandwidth, and the whole point of the op-amp is that you can
trade one for the other. If you want wide bandwidth at high gains,
you need a whole lot of open loop gain inside the box, and that
means a big box with a lot of tubes in it. And it means some drift
issues.

For most of the things op-amps got used for back then, drift was
critical. If you didn't want response down to DC, there were plenty
of other solutions that were easier or cheaper (and often involved
transformers).

Look at those 1.8M plate resistors! Yow! Gain at all cost, indeed.
--scott

--
"C'est un Nagra. C'est suisse, et tres, tres precis."