bitrex wrote:

For a brief period transformers were cheaper than a set of tubes with
weird custom filament voltages, but that didn't last long.


Zenith, GE and other name brands continued to build high end sets
with power transformers. Some of the later Zenith TVS had a self
resonant CVT that sold for about 1/3 the price of the set.

Their cheap sets were all series filament, with a voltage doubler
for the B+.