Modern

The Quiz Pot
(Continued from page 32)
bit of work but is worth it as we gain a
lot of room in my small projection room."
The accompanying photographs indicate
not only a lot of uwrk but S07ne very fine
workmanship and careful pla7ini7ig. We note
the grill work on the "operating" side and
a triple row of perforations near the top
of the base on the "nonoperating" side,
undoubtedly for the purpose of ventilation
which is very essential. We predict that
equipment manufacturers will take heed
of Ray's idea since it represents a very
practical use for what has long constituted
waste space.
Projector bases are usually designed for
universal purposes, i. e.. for use with any
and all types of current supply and lamp
equipment. Frequently, generator equipment
is used, and when it is, the DC is
broken by the large switch mounted on the
base.
Since relatively heavy amperage at low
voltage is involved, the large Knife type
switch is needed. On the other hand, with
a specialized set-up like Ray's, using a
single-phase 220-volt 9 amp. rectifier ivith
the switch breaking the AC, we tvould be
in favor of a much smaller switch, permitting
a tnore compact installation, although
it should have at least a 30-amp.
rating as the "inductive kick-back" of the
primary winding is a bit rough on contacts.
Or, using the same switch, in the
process of manufacture, provision could be
made for the wiring to run directly from
the inside of the base into the switch,
thereby concealing all switch wiring. One
popular type of base houses the sioitch
which is operated by an external lever.
With the thought of one manufacturer
producing a complete base, rectifier, and
lamp unit, we can go a bit farther and
suggest extension of lamp ventilation into
the base, affording a degree of forced draft
for further tube cooling efficiency.
Congratulations on a very fine streamlining
job, Ray!— G.B.
Here's a space-saving idea for the small projection room— installing rectifiers in the base of
the projector. Submitted by Ray S. Hanson, Fertile, Minn., this indicates not only a lot of work
but some fine workmanship and planning.
different acceptance of almost any weird
effect brought to his attention. Therefore
we offer no apologies for our gullibility as,
mopping our receding hairline, we studiously
explore the possibilities of the described
effect, finally emerging with our version of
an explanation:
Since the advent of theatre sound, it has
teen generally conceded that a direct current
source of excited lamp supply voltage
is preferable to alternating current for the
reason that there are certain disturbances
present in the reproduced sound when 60
cycle AC is used, although in recent years
advances in engineering have largely overcome
the disadvantages. Some equipment
manufacturers have solved the problem
through increasing the frequency of the
current supply, through the use of an oscillator,
to approximately 20 kilocycles, and
this type of exciter is rather widely used in
16mm equipment. Since a 20 KC note is
"super-sonic"—beyond the range of hearing—whatever
disturbances may arise
therefrom may generally be disregarded,
and exciter lamp operation on "raw AC" is
thereby achieved with no detrimental effects.
Moreover, the thermal lag of the
exciter filament tends to eliminate photocell
excitation at this frequency by the light
source.
Nevertheless, tests of such equipment
have indicated that it is entirely possible
for a 20 KC note to be introduced into the
amplifier circuits through induction, and
very strong signals at this frequency have
been found to be present in the output circuit.
It is entirely conceivable that current
of this frequency, sufficiently amplified,
could radiate a considerable distance
under favorable atmospheric conditions
perhaps with the speaker line acting as an
antenna.
With the oscillator and amplifier operating
from a common power supply, we
ponder the possibility of oscillator modulation
resulting under which circumstances
we come up with the thought of a "modulated
carrier," a condition duplicating regular
radio broadcast.
And until someone proves our ex-GI a
prevaricator or fabricates a better solution,
we are doggedly clinging to our version as
we have figured it out. In the meantime,
we'll be looking for mail from our licensed
radio amateurs of whom there are many
among the projectionists.— G.B.
EX-GI OPERATOR
A story passed along by an ex-GI operator
of a South Pacific island locale has
plagued us no end for a possible solution.
In all sincerity, the boy tells of operating
16mm sound equipment in the open air.
and a public-address system several hundred
yards away picked up and reproduced
the sound.
The phenomena of theatre sound equipment
picking up and reproducing sound
from regular radio broadcast stations is
not new. but the idea of a motion picture
sound system broadcasting to a public address
system seems a bit fantastic. However,
a couple of decades of association
with the fantastic science of electronics
would resign even the most dubious to in-
Meeting recently to discuss the peculiar problems of acoustical design and theatre service in
floating theatres, were the officials and engineers of the RCA Service Co. and the Grace Lines,
pictured on the promenade deck of the latter's "Santa Rosa." Left to right are Josh Billings jr.,
RCA Service Co., Inc.; Frank Quinn, marine paint division of DuPont Company; O. B. Hanson,
vice-president and chief engineer, NBC; Godfrey MacDonald, general traffic passenger agent,
Grace Lines; Richard Carnis, RCA Service, and John Sullivan, purchasing agent, Grace Lines.
34 The MODERN THEATRE SECTION i