Page 6 - RD_2007-06

THE WORM MUST TURN
By Alan E. Lott

Of recent months there has been a to good working order. When switched
surprising resurgence of interest in the on the cooling fan ran, the main drive
motor ran and the lamp lit but the
hiring and collecting of 16mm films. This film transport system did not operate.
means that an increasing number of On removing the rear cover the fault was
16mm sound projectors are being obvious. A large white plastic worm
brought back into operation. It is very wheel mounted on the main drive shaft
probable that of the various makes Bell & had shattered into several pieces, which
Howell machines of varying models and were scattered about the bottom of the
case. This worm wheel, about the size of
ages will be the majority. Spares and a cotton reel, had a metal core and the
servicing for most of the B & H plastic worm was moulded on to this core.
machines are normally readily available Presumably, over the year s ,
from repairers who advertise in ACE. differential expansion and contraction
The older B & H projectors of the 600 between the metal core and the outer
plastic worm proper had split open the
plastic, which had then shattered under
the load of driving all the mechanism.
Telephone calls to several agencies
offering repair services revealed that
t hi s w as a w el l - k now n pr obl em
amongst repairers. B & H later rede-
signed this worm wheel as a solid one-
piece construction in a different material,
which does not suffer from these
catastrophic failures. Unfortunately to fit

series were built like the proverbial the redesigned replacement it is
battleship: the most likely source of necessary to virtually dismantle the
problems being the thermionic valve greater part of the mechanism, which
amplifiers, but normally these are readily with the rebuild can take five or six
repaired. Replacement magnetic heads hours providing that no other problems are
for the 600 series tend to be in short discovered in so doing. Also during
supply and are expensive when reassembly it is advisable to use the B &
available. However these are not a H jig to ensure correct operation of the
requirement for the optical sound films for hire
or purchase. auto-threading system... Although I have
The later models in the TQ series are a complete B & H Parts List and Works
much more self-contained and have a Manuals for the TQ3 series I decided
performance much superior to that of that this was one task I would rather not
the 600 range but their mechanism has tackle. Also on this machine it was
an Achilles’ heel.
This came to my attention when a young obvious that two other small items

lady was sent to me by a mutual friend. needed attention so eventually I agreed
She had been given a non-working TQ3, with the owner that she would send the
Model 1692 which she wished to restore 1692 to Sound and Screen Services of