A couple of shots of a BTH 452. There was a series of similar machines, going back at least as far as 401, and including ones with mag sound as well as optical. All were the same basic design, but with many detail differences. I had four, each with a different valve set. They have irritating mains connections, ranging from the B&H Jones plug type on the 452 to seven-pin speaker type on the earlier machines. The pin configuration on the Jones plug is not the same as B&H use. The seven pin type have me utterly confused, as each pin has its own wire, yet there can only be a max of 3 wires in from the mains (or is it 110v for some with extra wires in and out for a resistance?). Does anyone have the workshop manuals and/or circuit diagram? I really don't want to do more damage than time and neglect has already wrought.

I am currently in the throes of trying to sort them all out. The amps all have the main section on rubber mounts to avoid projector vibrations affecting the sound, and are actually easy to remove once you figure it out - only about three screws and the entire unit lifts out.

I suppose a major part of the appeal of these machines is the decidedly eccentric layout. That curving film guide over the claw mechanism is not something I've seen anywhere else. A single-sprocket sound machine is also relatively unusual, with the lamp at the back reflected thru, as for many silent machines.

Chris McCabe has provided some useful info on these projectors:-

"The 452 was a mains voltage machine; the 450 and 451 (mag/optical with the extra preamps in a wooden
plinth) were 110v.  The Belling Lee 7 pin plug assembly was needed because not only did the transformer case supply 110v for the motor and lamp,

but also the entire exciter and amplifier voltages, including a U52 rectifier valve in the case. Therefore, the projector main unit is not self contained.

Unfortunately these power supplies are usually missing. I have a nice 451 in this condition. If you come across such a power pack spare please let me

know. I do have the technical data and service book for the 450 series around somewhere if you like I will try to find it if you want the pin connections.

Obviously one can lash up the machine to run motor and lamp from 110v just to see the wheels go round and the other circuitry could be provided but

frankly although the machines look nice and contain a lot of engineering (like the gear driven fan!!!!) the results can easily be bettered by a 601."

Bill Kilgour sends some pix of a very rare beast, a 451 with magnetic sound and a mag sound unit bolted on underneath.

I don't think I've ever seen a BTH transformer before; as Bill points out, the amp is not just powered from the tranny, its on/off switch is there, too.

Even rarer must be the Xenon version I found in a mag.

This is a superb pic of an earlier model, courtesy Ron Ashton.

BTH 301

Bill Kilgour has provided a write-up and many pix of a BTH 301, which looks like he's restored it to a very high standard.

All the stuff in quotes  below is Bill speaking.

" The BTH 301 16mm optical sound projector arrived in the autumn of 1947 from a company perhaps more famed for its

professional 35mm cinema machines. With  impressive black wrinkle finish and  stripes running over the mirror box and

lens holder, it had  something of a streamline art deco appearance.   BTH used similar stripes on their 35mm SUPA cinema

machines. (These were single unit projectors, not made up from separate parts such as  picture head, sound unit and base,

which might be from different makers.)

A brand new 301 would have set you back £220, a tidy sum in those days. Competitors included the Bell & Howell 601

at £237 and the Ampro Premier 20 at £213.

The BTH was not the quietest 16mm machine on the market but, to be fair, it was not designed for the coffee table

in the living room. It was more at home in the back of a village hall, operated by the mobile film units that toured

rural areas in the forties and fifties.  I spoke to the owner of a business that hired out these machines, who spoke

very highly of them and told me they would just run and run.  If one did seize up, it would go in to the workshop,

get doused with oil and be back on the road again.  I got the feeling that, unless a machine actually seized up,

it never would get into the workshop.

The 301 can be quickly set up ready for use.  With its single sprocket, the machine is

surprisingly easy to thread, especially if you have experience of lacing an Ampro

Premier 20, and the 301’s simple threading path path is kind to film. The gate tilts fully

forward for easy threading and cleaning of the independently front sprung runners. 

A thumb screw locks the lens in place. (TQ3 take note).

The British engineering is of a high standard, using helical gears for the main drive. The mechanism

turns smoothly on 14 ball bearing races (16 if you include the motor).  Speed change from 16fps to

24fps is effected by a gear lever placed under the single sprocket. There is no reverse gear.  The

take-up drive is through two large discs with a driving roller in between, a design dropped in the

401 series, possibly because no one could fathom out how it worked or how to adjust it.

It sports a powerful A.C. capacitor-start induction motor at a time when the competition was still struggling on

with centrifugal sparking contacts for speed control. The mechanism Is very easy to turn over with the inching

knob and rolls to a stop after switching off. Nice that.

The lamp is a pre-focus, 115volt, 750watt with the light beam turned 45 degrees via a mirror

box onto the gate.  I’m never happy with reflected light but it seems to do the job and lamp

changing is very easy (when cold). Cooling air is forced round the lamp via a cowling from a fan on

the main shaft, another high speed gear driven fan sucks air in at the base.  Fan speed is the same

for 16 or 24fps. 

The large diameter sound drum is part gear driven via a felt clutch.  A pinch roller above the drum

gently nips the film to cancel flutter, rather than press on the drum. The roller swings forward for

threading.  Adjustable slit focus is incorporated to allow for emulsion on either side of the film

(this was early days).  Above the exciter lamp is a thumb screw for centering the  4volt 24watt

exciter lamp on the sound slit for maximum output. A well-used adjustment.

One feature included, and I wish other projectors had this, is a sideways tilt screw on the rear

right-hand corner, which saves looking round for a beer mat. I don’t like tilted pictures on the

screen any more than I like muck in the gate; perhaps I’m too fussy.

The intermittent unit is held in place by two bolts with shims to allow adjustment of gear meshing. 

For sound projection, the dual bladed shutter is used in the single position, and  to counteract flicker

at silent speed, the extra blade is opened out. This feature was not available on the first models. 

Only two claws move the film through the gate, not the three we now accept as standard but, remember,

 these machines would be running near mint prints in the fifties, (mint 16mm print, dream on)  so two would be

plenty. The spring loaded claws slide over the film surface until lined up with the perforations, unlike some machines

that will then attempt to punch a new set of holes.

For servicing, the 10watt valve amplifier can be quickly detached by removing one large screw and disconnecting two

4 pin plugs; the photo cell is withdrawn from underneath the machine.  In fact, I have never come across a projector

so easy to dismantle. The fuses are not in the projector but on the front panel of the 115volt mains transformer, along

with a  voltmeter socket.  When not in use, the transformer  lives in the  speaker case with the large 12in.  speaker. 

Transformer and speaker together? Try and lift that lot off the floor.

301’s turn up on eBay from time to time but never seem to have the all-important transformer,  now

considered as rare as hen’s teeth. The diagram should help those who have the projector but no

transformers. The side cover gets lost as well.  For some reason, sales of the 301 were never as good

as they should have been, perhaps due to the popularity of the American-designed Bell & Howell 601.

Now, some sixty years later, a British Thomson-Houston 301 in its majestic wrinkle-black livery is a nice addition to a

16mm projector collection. Thanks to a host of spare parts from Sound Services Ltd (who had acquired the entire BTH

stock of bits in the 1960’s), the 301 pictured is still working and projects a nice steady picture.

Bill Kilgour"

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As a sort of coda to Bill's stuff about the 301, here are pix of a 301 with a blimp. Until seeing this particular machine,

I had assumed that the metal machine shown above was all there was. In fact, there was a three-part blimp, presumably to

reduce sound  levels. It would seem that these rarely survive, and I can see why - it's all a little on  the fragile side to

withstand the slings and arrows of outrageous fortune. And the projector is fine without it, really - I can't imagine it actually

did much good, and even without it, the machine had a handle for carrying and spool arms that folded out of the way.

In the pix above, I have made the machine do a strip-tease, purely for scientific reasons, of course. The front section of the

blimp in Pic 1 is secured at the top by a single catch, to the right of the carrying handle. The bottom of this piece is held by two of

those partial hinge things, where what would be the centre section of the hinge is incomplete, so that when folded down,

as in Pic 2, it comes free. The rear blimp piece and the cover for the speaker use the same kind of fitting. Note in Pic 1

the cut-outs for the sound controls as well as as the rather oddly-placed lamp and motor switches. Pic 2 shows the large cut-out

along the top of the blimp component for the spool arm and the threaded film.

The back section of the blimp is much more robust, being secured by two substantial catches to the base section of the blimp. This

is pretty strong but, particularly if the front section is not in place, can be a bit wobbly since it is not secured to the machine itself.

The top  of this piece is left therefore with a degree of  movement from front to back, which feels a tad insecure. Note also that

this part of the blimp has to be folded back at least partially to allow the spool arms to be unfolded.

Finally we have the base, secured to the projector from below by two substantial bolts. A cut-out is left for the adjustable front foot,

and for access to the photocell, which is removable from below.

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I have now found a workshop manual for the BTH 450/451, so here it is. Amendment slips have been added to some of the pages and overlay the original text. I have therefore given "with" and "without" page versions.

These pix are from photocopies, so not as good as I would like. Originals or good scans thereof welcomed.

This one is much earlier.

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