"Bret Ludwig" wrote in message
oups.com
Ruud Broens wrote:

snip


The opamp is *designed* to use large amounts of
linearising
feedback, something that simply isn't an option with
the inherently much lower open-loop gain of tubes.

Philbrick and Julie were building perfectly proper op
amps with tubes as early as 1943, but thanks for playing.

Actually, tubed operational amps, especially the early ones (the specific
ones you're mentioning), were horrors. If the noise and drift didn't get
you, the short parts life would.

Operational amplifiers were originally designed as parts for analog
computers. When SS op amps for analog computers became commercial, analog
computer experts sighed a huge sigh of relief. They were stable, reliable,
and quiet.