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One of the principal exhibits of this firm is cathode-ray apparatus, among which the 12H tube, designed for television purposes, is of especial interest. It has a screen diameter of 30 cms. and an overall length of 62.5 cms it is rated for a maximum operating potential of 6,000 Volts, and requires about 1,000 Volts for the deflector plates. It needs only 20 Volts for modulation, however. Smaller tubes shown are the AH, BH and CH, with screen diameters of 7 in, 5 in, and 1 in, respectively.
The Ediswan 12H television cathode-ray tube.
A full range of Mazda valves is on view, including HF pentodes with 'top-grid' connections and a new output triode. This has characteristics the same as those of the older PP3/250, but in order to maintain mains hum at a minimum the filament is rated for 2 Volts only; it consumes 2 Amps. Transmitting valves find a place on the stand, and types specially designed for operation on short waves and ultra-short waves are to be seen.
The well-known BTH needle armature pick-up is shown, as is also the Minor pick-up, which is priced at 17s 6d, including volume control. The BTH piezo-electric pick-up has a wide frequency response and is highly sensitive. Complete with tone-arm and pick-up rest, it costs 2 guineas.
Ediswan accumulators and Tungar battery chargers are also on view.
The Ediswan MRAC1 and HEAC1 relays have been withdrawn and replaced by a range of Mazda Thyratrons, of which the T1 rand T21 are equivalent to the MRAC1 and HEAC1 respectively. The T31 has similar characteristics, but is argon-filled. Four 12 in cathode-ray tubes are to be seen working on this stand.
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