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Technical facts you always wanted to know....

Why do rectifier valves have 5-volt heaters?

The first mass produced consumer tubes, '00 and '01, had 5-volt filaments to allow reasonable service from a 6-volt wet-cell battery via a rheostat. Then, early AC tubes went to multiples or sub-multiples of 5: 1.25, 2.5, 5, 7.5, 10 etc. The 2.5 and 1.25 volt units were designed that way to help control AC hum. The later development of the car radio precipitated the more familiar 6.3 volt standard which is more appropriate for a 3-cell battery being float-charged by the vehicle's generator (actually more like 7 volts). [Al Klase - N3FRQ]

What are the true derivations of connector names?

BNC = Baby (or Bayonet) Neill Concelman. A baby-size combination of the designs of Neill and Concelman.

C = Concelman. Developed by Carl Concelman of Amphenol.

DIN = Deutsche Industrienormen Ausschuss (German standards-making authority, similar to our British Standards Institution).

EIAJ = Electronics Industry Association of Japan.

MUSA = Multiple Unit Steerable Array. Developed in the 1930s by the British Post Office. It is very similar to the American Western Electric video jack.

N = Neill or Navy type. Originated in 1942 by Paul Neill of Bell Labs and standardised on a Navy Bureau of Ships drawing.

RCA = Radio Corporation of America.

UHF = Ultra High Frequency. Developed in 1940 by E.C. Quackenbush of the American Phenolic Corporation (later Amphenol). At the time this connector was designed, UHF meant what we call VHF today.

What happened to BBC Television's mechanical globes once they were no longer used for on-screen continuity?

We're told on good authority there is a BBC globe that is jealously guarded in a cupboard at Pebble Mill. Another globe is located in the reception area of the BBC R&D facility at Kingswood Warren.

Why did early television cameras have two lenses? In the course of the programme, a 1936 BBC camera is shown and reference made to its two lenses causing a parallax error. At the risk of sounding very stupid, why two lenses? One for the programme material, one for the viewfinder?"

Yes, the old Emitron (and some foreign cameras) had two lenses, one for the pickup tube, and one for the viewfinder, which produced a backwards inverted (i.e. upside-down) image. The cameramen (and I knew several in the early 1950s) got used to looking at the inverted picture, and even panned in the correct direction when necessary. CRT viewfinders weren't generally used until after the war, though Du Mont in the States did make an Iconoscope camera before Pearl Harbor with a CRT alongside (in a separate enclosure from the camera head). [Arthur Dungate and Ed Ellers ]

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