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In Reply to: A story from long ago..... posted by doodlebug on December 4, 2006 at 21:08:12:
Transmitter tubes were a different animal. Most transmitting amps were located outside the main TV station in a separate room - for obovious reasons. The story I related had to do with all the small-signal processing that went on in the studio itself. There were plenty of racks of gear for switching and managing the network feed as well as inhouse production. This is where the technique I mentioned was applied. If you had Walter Cronkite on a 7PM doing the news and you lost your video to the transmitter, what did you do? Remember this was live!
All radio and TV transmitters had regular maintenance schedules and the FCC in those days required that all meter readings and maintenance logs be kept up to date. Failure resulted in loss of operating license. The FCC was mainly concerned with poor transmitting performance and didn't really care if the feed was lost. In fact, part of the records required that an engineer go out into the field and measure the amount of RF from the broadcast station to ensure that the radiating power was correct.
You didn't go near those transmitting tubes without first shutting it down - many small animals found out why the hard way. What we now know as the Darwin Awards took out those engineers who didn't pay attention.
I have experence with very large Navy missle fire control radars from the '60s. But were talking about much more power at much higher frequencies.
My Dad was a Radar Officer on a carrier in WWII and he told stories about the birds that were perched on the radar antenna would get fried when they fired up the radar... Early example of microwave cooking I guess :)
I always thought it was dangerous to mix extremely high current and water, but many transmitting tubes were/are water cooled- they have a water jacket around the base with inlet and outlet.
A friend gave me what is really a modest transmitting tube, marked as a Mazda. The tube appears to have never been used. It's a two pin- the pins are perhaps 12mm, envelope is about 50cm long and 10cm diameter- and air cooled. It interesting in that it doesn't have any kind of getter, there is a small handful of granular metal chips and I'm told this material soaks up any outgassing of the materials. It's very odd to have a tube with all this heavy, free grains in inside- it must be extremely non-conductive. There are also interesting manufacturing notations both inside and between the pins by several hands, suggesting a lot of hand work and individual testing.
It seems an attractive idea to build 4000W monoblock amplifers with a couple of tranmitting tubes. Besides the power, I imagine they're very linear and dynamic too, but imagine having to call the plumber when you need to move your amplifier to another room!
Imagine a humongousoid triode in parallel with an elctrostatic speaker...cathode connects to one surface, plate connects to the other surface, and the dynamic voltage across the triode is the voltage across the 'stat. Talk about SET OTL! The tube would simultaneously bias and power the 'stat. Cooling and safety? Minor issues, right?
I like your idea very much- it has a kind of purity to it and we all know how delightful are tubes and electrostatics!. -I'd keep the power supply in the garage next to the blower for my home pipe organ!
For more tube-use perversity, see my post above: "I once had singing 6H23p's (6DJ8)- Plus, an idea for a homemade ribbon microphone".
I don't know about TV stations, but my understanding is that transmitter tubes are still being used at radio stations - apparently for signal transmision there are some jobs that tubes can do more efficiently and cheaper than transistors.
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