Back in the 1950s and 1960s a few vacuum tube PAs were sold that did not use
the conventional plate-tuned circuit, but used broadband tranformers. They
died an early death, thank heaven.

Push-pull tube amplifiers with link coupled coils etc were very difficult to
TVI proof. The pi-network (and pi-ell) with tubes in parallel was a big
improvement.

Bill W0IYH

"Highland Ham" wrote in message
...
" I just noticed in this ad: http://hamstation.com/ybstkftmk5.htm that
Yaesu's FT-1000 finals are MOSETS in push-pull. I don't ever recall
seeing a pair of final tubes in an xcvr or linear in push-pull except
perhaps way back in a very old QST. Can someone explain why push-pull is
used in the Yaesu and why we don't see it in "modern" tube amps?
=============================
Tube amps with 2 output valves can be used in push- pull but then for 1
band
only unless you would switch multiple inductors.
A single valve or multiple valve in parallel can readily output into a
multi-band PI filter arrangement.
In QST -March 1967 , pages 11 - 15 there is an article on a 1kW amplifier
for 50 MHz with 2 pcs 4-125A or 4-250A or 4-400A push pull . This is a
single band amplifier with inductive coupling on in- and output.
Unless you would perform band switching by changing the inductors through
plug-in , switching for various bands would be very complicated.

Frank GM0CSZ / KN6WH.