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.

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

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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