On Mon, 17 Dec 2007 09:52:30 +0000, David Looser wrote:

Interstage transformers, as used in the distant past to couple the
signal from the anode of one valve to the grid of the next. They went
out of favour in the 1930s when higher-gain valves made RC coupling more
useable.

And transistors made the whole bloody lot obsolete before most people who
still have their hearing were born, thank goodness. ;-)