John Rutosky writes in the MMD for 01-09-20:

"The tympani effect in a Wurlitzer 165 Band Organ is a single stroke
pneumatic that plays the bass drum, and the reiteration is punched
into the roll.  As an exception, I know of one style 165 that has an
alternating 2-pneumatic tympani effect, and along with that the main
bass drum beater is suction operated like an orchestrion, meaning it
is not operated by exhausting the pressure as is done traditionally."

I can't argue with John's first sentence except to note that all the
many tympani actions on 165 organs are retrofits, so they can be
whatever the maker wants them to be.  It is true that single-stroke
actions are the most common, and they also sound the best, in my
opinion.

I once began to look at style 165 rolls to answer the question,
"reiterating or single-stroke," but I stopped when I found, in the
rolls I did look at, both bass-drum-type (single stroke) and
snare-drum-type (reiterating) perforations, depending (I assume) on
when the roll being examined was made.

It might be interesting to look at all 100+ Wurlitzer and T.R.T. rolls
and chart the kind of perforation found and the date of the roll in
which it is found.  I could do that, as I have recuts of every existing
roll, but it's not a high priority with me.  The amount of tympani cut
into a roll varies immensely from period to period, the foxtrot rolls
of the '20's having little or none.  Surprisingly, a few rolls of the
late Wurlitzer 6-tune era (late 1930's) have waaaaay too much, the
tympani playing throughout a tune whenever the bass drum is not
playing.  That was J. William Tussing's arranging, I'm sure.

John's second sentence may explain why the Seabreeze Verbeeck 165
replica uses a vacuum-driven bass drum beater and a two-pneumatic
tympani effect.  Johnny Verbeeck took the specs for the replica from
Bob Gilson's Wurlitzer 165, and if the organ John is speaking of is
Bob's, then Johnny faithfully replicated what he found there.

The vacuum-driven bass drum isn't quite as snappy as the Wurlitzer
vacuum/pressure one, but it is nearly so -- in spite of the smallish
size of the pneumatic -- due to vacuum supply and secondary valve being
right at the beater pneumatic.

The two-pneumatic tympani action on the Verbeeck can be viciously
aggressive (as it is on the Klavier CD's of the Gilson organ)
especially when the roll being played uses snare-drum type
perforations.  When playing one of the J. William Tussing rolls
mentioned above, I simply disconnect the primary for the tympani to
silence it.  A waltz like "Drifting Along" doesn't need a constantly
pounding tympani.

Mathew Caulfield