I found this remarkable set of books during lunch while searching
for information on 715B radar modulator tubes. That search led to
this URL which discusses the use of the tubes, and design lineage
from WWII requirements to the 5D21 pulse tetrode.
http://www.alcatel-lucent.com/bstj/vol26-1947/articles/bstj26-4-818.pdf
Which led me to this remarkable treasure trove of books, the complete
Bell System Technical Journals from 1922 to 1983.
http://www.alcatel-lucent.com/bstj/
Which led to a phenomenal reference of using spark gaps in radar
modulators, with loss measurements!
http://www.alcatel-lucent.com/bstj/vol25-1946/articles/bstj25-4-563.pdf
Probably more spark gap and radar modulator type circuits in this
technical series and maybe additional tube stuff germane to VTTC's.
WOW what a reference!