Home Talkie



BB1  BB2  Super Rural Rural Sonore  17.5



I related in my Introduction to 17.5 how I came to acquire a Home Talkie. Obviously, the first job on acquiring any old projector is to take it apart (very nostalgic - doing this with 9.5mm Babies was one of my early experiences and is very therapeutic). Just as well, as mine was not only without any earth wire (normal for its time) but had perished insulation and exposed bare wires on the mains lead inside the casing. After that, job two was to drill a hole and fit a separate lamp switch. As I never throw things away, I had one of the same pattern. Third job was to replace what I assume was originally a rubber pad under the mechanism for reducing noise and vibration. The influence of time, oil and heat had turned it part crumbly, part liquid mess, nasty to remove.

17-5-9.5sbig-brotherFourth job, converting to QI, was more complex. The original lamp is 16v 8 amp, with provision to overrun at 17v and underrun at 8v, for reasons which are not clear to me. I decided to go for 15v 150w. I thought if I left the mains input setting at 250v, this would give about 15v since our mains is now about 230v. As for the increased amperage, I just hope the original transformer was over-engineered. The lampholder is mounted to a rod which fits inside the original lampholder without making any permanent alteration.

The new lamp did however mean some form of cooling would be prudent. I wanted to avoid as far as possible any irreversible changes to the machine, so I made an aluminium ring which is a push fit into the lamphouse in place of the plastic end cap, with a slight lip to stop it going in too far. On this is mounted a 40mm, 12v computer fan from Maplin, which can be seen in the pictures. It is set to blow rather than to suck as it says on the packet that the fan is good only up to 70 degrees C. I thought the lamp might deliver more than this if the fan sucked. To provide a DC power supply, I had to build a small unit from a kit (Maplin again) and wire it into the lamp circuit so the fan comes on with the lamp. Power lead goes behind the sound chute and plugs into a socket mounted alongside the lamp and motor connections. (The holes for this and for the lamp switch are the only permanent changes from the original). Future options include a shield to keep the direct airflow away from the lamp (they go black I am told) and another to reduce light spill out through the fan. A higher power lamp (probably fed from an external 24v 250w ex-Elf transformer) is also a possibility, as I find the light is still on the dim side. The power supply for the fan has a variable output so there is some cooling capacity in reserve to cool a brighter lamp.

The original amplifier didn't seem to work and I don't regard them as worth bothering with anyway (times change - I wouldn't say that now [2015]). So I just took out the valves and fitted a solar cell. This is a bit of a clunky affair, being designed for 35mm and in a big casing, but it does the job and precision in mounting is far less critical. The solar cell mount is screwed to a small metal block with a through hole. The original sound mirror can be unscrewed, leaving a rod which goes into the aforementioned hole in the cell mounting block. The wire is led carefully away and under the motor, but left as a flying lead at this stage. It goes into a pre-amp I built years ago for my Super Vox (which never had an amp at all) and thence to a separate main amp. An integral amp is a longer term project. The alu plate above the sprocket is simply to keep the wire from the cell out of the way.

Even before I had a projector I made myself a 17.5 rewind adapter. I have a 35mm rewinder, Phillips type. The spindle size is the same as both 16mm and 17.5mm (and 28mm for that matter) and the drive to the spool fits into the notch in 16mm spool centres. So it makes a good 16mm rewinder with a 100ft plastic spool as a spacer on the outside, and a 17.5mm rewinder with the adapter (made from an old 16mm camera spool) on the inside.

I shall try to include some pictures to make all of this clear (at least, clearer than it is now).

The machine when I got it was in very good original condition and in its original box with matching speaker, and even the separate gate mask for silent film, but with one or two small touches that I had not met before. The mirror was held in place by a bracket, obviously original as it is painted the same colour as the machine, rather than just relying on the friction fit into its ball socket. This is a minor but important point as it is very easy to knock the mirror when threading. The other thing was the provision of two hand rewinders. These are small handles with pins that fit into the holes in the spools around the central spindle. I have previously only seen these for 9.5.

The machine also had all the old problems that I remember, with some pretty fundamental design flaws. First, it has a single sprocket. The amount of contact between the film and the sprocket is therefore very limited. Correct threading is tricky yet absolutely critical. Putting the film through for the take-up easily dislodges it from the feed side. I have seen hundreds of feet of film dented all along the side where it has not been seated on the sprocket pins properly and, of course, many of these dents end up wrecking the sprocket holes. The feed loop is lost and the claw then attacks the perforations.

This leads to the second basic flaw. The feed loop is not only ridiculously short, but the sprocket is offset in relation to the gate (The 9.5 Vox is like this but with a much longer top loop to give a bit of leeway). As far as I can see, there is absolutely no reason why this offset has to exist. It is all the more odd as the film has to come back across again as it goes around the back of the lamphouse, to meet the take-up side of the same sprocket. These two flaws together mean the machine is very unforgiving; there is no slack in the system and the slightest hitch leads to instant damage. The powerful motor has a fair bit of momentum and can run on causing damage over some length of film. 

The third flaw is the sound smoothing system. It uses a chute (a similar arrangement was later used on the 9.5 Pax, although the 17.5 one has one side hinged to allow the film to be inserted). There is no additional smoothing between the sound reader and the sprocket. And the wrap around the flywheel is too short. The chute is a particular problem. The instruction book specifies that the film must be pinched together from the sides to take up a bowed profile. With side sprockets this is asking for trouble at the slightest weakness in perforations . Any misalignment of splices is likely to be a problem too. 

The final major flaw in my eyes is the lamphouse. Because it is enclosed by the film path, it cannot be enlarged and has minimal cooling from a crude fan on the motor shaft. The same lamp also serves for the sound. Some further comment, relating to the single sprocket and its problems, can be found in Aunt Em, under 17.5 Talkie.

Well, all this lamp fiddling didn't work. With the 15/150, the lamphouse becomes unbearably hot, far too hot in my view to use because of a risk of serious damage. So I tried a 24/150 instead. Rather to my surprise, it worked, tho' light output was obviously well down. Tho' the lamphouse heating problem was less bad, I was also now finding the motor getting much too hot and feared I might cook the wiring. So I tries the front-mounted fan I mentioned earlier somewhere. (Again, all without making any alteration that I cannot reverse.). This cools the motor, but not the lamphouse.


On once more taking up the cudgels to battle with 17.5, I tried a new approach. A piece of 1cm plastic channel can have a fan bolted to one "leg", and the other leg fits rather neatly under the lip of the amplifier cover. I tried this with an 80mm DC fan, then ditto mains, then both, directing air onto the back of the lamphouse. Didn't work.

At this point I started to get the bit between my teeth and decided to have a bit of fun. I got a 120mm mains fan, two "reducers" to drop the aperture to 80 then 60mm, then a piece of semi-flexible 60mm ducting from Halfords. I made two aluminium adapters, one to go in the end of the lamphouse to take the ducting (see below left, looking straight into the lamphouse; the lamp can be seen in the centre), the other to go on the "reducer" and again provide for coupling up the ducting. I tried this first with just one stage of reduction and the 80mm mains fan. Could hardly feel anything coming out of the ducting; most of the air seemed to be going out the wrong way at the back of the fan! Then on to second stage of reduction and the 120mm fan. You can see the total assembly to the right. (Note the mains switch for power to the 80mm mains fan mentioned above which, with the aid of a large washer, fits into an existing vent hole in the amp cover). Finally, this did give me some air, but frankly not a lot and again most of the air coming out of the fan the wrong way. Seemed rather better when I set it to suck rather than blow. At this point, I got a bit discouraged and went away without actually testing, which I suppose I'll have to do. Not very hopeful tho'. (No idea where I'm going to put the fan anyway - no room on top of the projector.) What next? Maybe a hair dryer with the heating element disabled?

home-talkie home-talkie home-talkie

This is what I ended up doing in order to test. We in the trade have a technical term for this - we call it "a right lash-up". Two 80mm fans, one mains and controlled by the switch seen in the previous pic, one 12v and wired to come on with the motor, are providing external cooling. The big fan with the ducting is connected separately to the mains and set to blow and held roughly in place by some orange wire; the 80mm DC fan at the front of the machine is disconnected at this stage. With a single reel, there was some evidence that the lamphouse was rather cooler than before, so I was emboldened to try a full 1000ft. This, too, seemed to be OK, but it was noticeable that the motor was starting to heat up quite a bit. Next test is with the big fan set to suck. If this works, I can eliminate the front fan; if not, I shall have to wire it back in.