Early Picture Tube Configuration question
 

My nephew just saw a 1939 RCA Television up at Roosevelt's Estate Springwood.
He wanted to know why the tv tube was mounted vertically and a mirror was used for viewing.
The answer he was given was that early television was received upside down and backwards-which is nonsense electronically.
So I went out on the web digging, thinking it might be either the early glass technology and vacuum stability OR early electronics dictating a longer neck to accelerate the beam.
But no one seems to touch on this little fact on the early TV websites.

Before I spread misinformation does anyone here know why the larger screen size (12") CRT's were mounted vertically in 1939??

I know they had long necks but why the long neck when by 1941 they were mounting the picture tubes for direct viewing?

Did they need the length for the deflection technology of the time, or was it because they used electrostatic instead of electromagnetic deflection?

I originally posted in the tubes forum, not seeing this forum. A member pointed me over here thank you.



Thanks
jon

You are correct, it is the longer neck on the early 12" CRTs. It was mearly a device emplayed to allow a realtively shallow cabinet. There were a few sets made in the late 1940s with mirror in lid configurations, but none after that.

The earliest CRTs used in TV (1929-32) were electrostatic deflection, had small screen sizes (3-5 inches), and very low deflection angles.

Early magnetic deflection tubes, developed about 1936-37 and later manufactured as the 9AP4 and 12AP4 had deflection angles of about 35 degrees. This made the tube very long, and it was mounted vertically to keep the cabinet from being too deep in the 12 inch sets sold by all US manufacturers:

http://www.earlytelevision.org/rca_trk12.html
http://www.earlytelevision.org/ge_90.html

By 1939 the British had developed much shorter tubes, with deflection angles of about 50 degrees. These tubes were mounted horizontally:

http://www.earlytelevision.org/baird_t18c.html

This page shows the 12AP4, along with the British CRM-121, one of the 50 degree tubes.

http://www.earlytelevision.org/crt_collection.html

Clearly RCA was aware of the shorter tubes available in Britain, but their interest was getting sets to market to test the public's response. If the war hadn't interrupted TV development, I'm sure RCA would have designed a shorter tube for their next generation of sets.

The most advanced prewar CRT was made by the Germans for their E1. It was rectangular and had a wide deflection angle:

http://www.earlytelevision.org/e1.html

Thank YOU Steve & John!!
Now I can answer the question correctly.