In 1930 a Harrow County project was the successful building of a "television receiver"...
I wonder how many boys on the school were privileged to inspect the small exhibition of junk and handicrafts held in Room 14 last November. As this exhibition was held mainly for the benefit and edification of the staff and inspectors, the number of visitors per day was probably fairly small; those who did drift in, however (possibly to work off the effects of School dinner in Room 13), may have noticed a queer contraption consisting of a large cardboard wheel, one or two electric lamps, an old electric fan motor, some coils of wire, and a few other odds and ends constructed with cardboard and Meccano, all mounted on a large broken drawing board.
Whether you believe it or not, the piece of Heath Robinson apparatus was a homemade television receiver which worked by a fairly powerful wireless set, had given very good results during the last Summer holidays. By this I mean that the head-and-shoulder views of people singing and talking in the studio of the Baird Co. in Long Acre, W.C.2, as at present broadcast by the B.B.C. were received with a fair degree of detail, it being possible to observe movements of the head, lips and ears (?) of the person being televised. Rows of printed letters (these are usually placed in front of the transmitting apparatus for the last five minutes of the transmission) were not received quite so satisfactorily, however, due to slight inaccuracies in the construction of the receiving apparatus, which as a matter of fact was only constructed as a preliminary experiment.
Of course, the pictures received were very small -- actually they were about the size of an ordinary vest-pocket camera photograph -- but this is only slightly smaller than the pictures received on the commercial model made by the Baird Co. and marketed at £26. Another slight objection to our homemade televisor was that the picture received tended to drift upwards or downwards at times; this tendency is counteracted to some extent in the Baird model by the use of a special "synchronising" device, but this is rather beyond Mr. Heath Robinson.
Besides their complete television receivers, the Baird Co. are marketing a kit of parts for the home constructor at £16, and both these receivers should give excellent results. As, however, the home-made receiver exhibited at school cost just under 6s. (six shillings), we may draw the conclusion that even if results are not quite so good, it pays to construct your televisor from the flotsam and jetsam of the home, or better still, of the handyman's workshop.
Now in case any of you think you would like to try to make a television receiver for yourselves, I propose to give you a few hints on how to set about it. First unless you have a good knowledge of the subject, derived from wireless periodicals, etc., I should recommend you to get the book "Television Today and Tomorrow," by Sydney A. Moseley and H. J. Barton Chapple (Sir Isaac Pitman and Sons Ltd., 7s. 6d.), also to commence taking the "Television Magazine," published by the Baird Co., price sixpence monthly. When you think you have a fair idea of the theory of the subject (it is much too long to go into here), you may begin to consider the construction of your televisor. By the way, before you start, it is almost essential to have the electric light available, also to have a good wireless set capable of delivering fairly large volume without distortion. For the former there is practically no remedy, but in the latter case (if for instance your set is of the ordinary two or three-valve type with only a small power valve in the last stage) a single stage power amplifier may easily be constructed for a pound or two; a super power valve and output transformer should be used and ample high tension must be available, a mains unit or H.T. accumulator being advisable.
Now for the televisor itself. The following are the chief articles you will need: (a) a fairly reliable electric motor which may be run of the mains; (b) a variable resistance of about 300 ohms, to be used as a coarse control of the motor speed; (c) a fine control resistance of about 30 ohms - a wireless rheostat will do excellently; (d) a Neon lamp, the cheapest and most easily obtainable form of this is made by the Osram Co. for 3s. 3d., but it must be used with a lens of some sort, to act as a condenser or diffuser (the lamp used in the Baird set costs 25s. and may be used without a lens, but the cheaper lamp gives just as good results); (e) a "scanning disc"; this may be obtained, made of aluminium and drilled ready for use for about 12s. 6d., but to start with a 20 inch cardboard disc which has been carefully marked out, is quite good enough: the holes may be punched with an Archimedes drill bit that has been filed down to a 1/32 inch square. In case you propose to make your own disc, it should be noted that the 30 holes form a spiral that travels inwards when the disc is rotated in an anti-clockwise direction; the motor, which may be connected to the disc-axle by a pulley and spring belt drive, should rotate the disc in this direction at 12 1/2 revolutions per second.
You will also need a few extras such as a baseboard and a bearing for the scanning disc, but the construction of these, as well as the assembly of the televisor when you have succeeded in collecting the components, I must leave to your own ingenuity; the television magazine should be of assistance to you in this direction.
Well, that's quite enough about the apparatus and method, and I don't suppose that what I've said will be of much practical use to many of you. However, if any of you actually succeed in constructing the genuine article, television transmissions are radiated from Brookmans Park from 11.0 to 11.30 every morning except Saturdays and Sundays, and from 12 midnight to 12.30 every Tuesday and Friday (these times are specially arranged by the B.B.C. to prevent schoolboys from trying out home-made televisors). In a few months' time, however, a new television transmitter that is now being built by the Baird Co. in South-West London will be working, and when this station is opened, much greater television reception facilities should be available. by the way, television transmissions are also radiated from the German station Zeesen (1635 metres) on Saturday mornings from time to time, but owing to a different system of transmission, the pictures received fron this station (if any) will be turned through a right-angle.
Now, what of the future of television? Well, to start with, if television is to become as popular as wireless is today, the price of commercial televisors will have to drop enormously. Secondly, the size of the pictures received will have to be increased wiry considerably and to balance this enlargement, much greater detail wil be necessary. And thirdly, the size of the receiving apparatus will have to be reduced. When, and only when, these improvements have been perfected, shall we truthfully be able to say "television has come."
P. Neal (VI)
Source: The Gaytonian, January 1931.