RADIO NOTES

Rotorua Morning Post, Volume 1, Issue 25, 22 September 1931, Page 5

RADIO NOTES

"Kathode."

By

Photo-eleetrie, or light sensitive, vaives - play an important fpart in television and talking pictures, and are particularly useful to the serious experimenter. Such a tube may be mad© from an ordinary 201 A valve, though, of course, tbe home-made product may not compare with the specially mannfactured type. To mak© such a cell, a 201 A tube should b© chosen which has a clear, silvery colour and not th© dirty grey, smoky colour sometimes found in such vaives. Having chosen a good tube, heat th© glass at a point opposite the plate. The silvery material will be driven from the glass .and will condense on the plate of the valve. In this manner a circle about an inch in diameter should be clear ed. This space now becomes the "eye" of the cell. Allow the glass to cool and the job is done. On the socket for the valve, join the gird and filament terminals. This now becomes the anode, while the plate terminal becomes the cathode. Yoltages from 50 to 150 may be used, but since the cell has a high internal impedance, the tube must be coupled to the amplifier by means of a high resistance. The development of radio receivers may be traced back year by year to outstanding technieal discoveries and improvements. Whole years may be identified by such produetions as power tubes, a.c. tubes, sereen grid tubes and clynamic speakers.' This year, the prevailing emphasis is placed on prices, though a number of interesting technieal developments appear and contribute materially to lower price levels. The penthode tube, for instance, has made it possible to reduce the number of vaives necessary for audio amplification. Selectivity has been reasonably maintained, though a sacrifice in fidelity has been made in a number of cases. Another development which is incorporated in a number of receivers is the valuable mu tube. In this valve, the amplification factor is a junction of the signal voltage impressed on the tube, the amplification factor decreasing as the signal voltage is increased. The effect of this is to increase selectivity or decrease cross talk and distortion. The superhetrodyne type of receiver is almost universally used, though the emergenee of this circuit is not due primarily to a technieal development, but to the release of patents which were held by the R.C.A. The Rev. William Constable, one of the most eloquent of Auckland's speakers will lecture on "The Spirit of "Ancient Greece" from 1YA this evening. The popular Melodie Four will contribute in such quartettes as "My Cairo Love," "Wanganui Moon," "Sweet Jenny Lee" and "An Evening Pastoral" from 2YA to-night. The New Zealand stations continue to be received with plenty of volume, though there has been a considerable falling off in trans-Tasman reception. The Australian stations will probably fluctuate from night to night before settling down to summer conditions. In "Xathode's" locality, electrical interf erence during evening reception has been considerably reduced, though it is still almost impossible to get clear reception during the daytime. Public interest in television is rapidly increasing. Developments along this line continue to progress slowly and regular image broadcasts are now being made in America. Full length figures are being reproduced and the receiving screen has been increased in size. Casting a speculative eye on the probable type of television programme of the future in the light of present sound programmes as received with static and local interf erence, one wonders if the images reproduced will ever be worth looking at. To receive clear pictures, all interference must be eliminated, and as yet no static eliminator has been invented. Mr. N. C. Pawley, owner and operatol' of ZL1FG is on holiday in Rotorua.