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Old 01-04-2010, 12:37 AM
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zenith2134 zenith2134 is offline
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lifespan transmitter driver amplifiers

Not sure how to put this but, Back when whole tv stations were tubed how frequently did the finals feeding the antennas need to be changed? I mean weren't many of them on the air 24/7 before the solid state age where some were even still used?*

Just stands to reason that by the nature of a thermionic device at those power levels it would always need swapping out.

* I'm starting a group about t.v. sign-offs etc and would appreciate any feedback on the subject...
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Old 01-06-2010, 04:52 PM
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Tube outputs are still in use.
Maybe someone with direct experience can comment on reliability.
Early stations did not stay on 24 hours a day.
Some stations install dual transmitters, so one can be off air if necessary, with a temporary 3 dB reduction in power.
High power solid state transmitters can be designed as many lower power modules, so failure of one or two is hardly noticeable.
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Old 01-06-2010, 11:15 PM
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By the way, reliability of electronic devices is often described by a "bathtub curve" having a component of infant mortality (decreasing with time), a component of constant random failure rate, and a component of wear-out (increasing with time).
Someone once explained to me that vacuum tubes start their life in the wear-out mode (due to constant depletion of the cathode).
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Old 02-11-2010, 05:40 PM
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I recall stopping by the transmitter site of our local channel 7 outlet. At the time, they were running 2 very ancient RCA rigs...big black boxes labeled "Abel" & "Baker". "Baker" was semi-defunct & the engineer was deep inside it trying to get it running so they could take "Abel" off the air for work. He was carrying a bushel basket full of tubes around while he worked....IIRC LOTS of 6146s in the basket. I should've asked what the final was...probably a couple of 4CX10000s or something.
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