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This topic comprises 8 pages: 1 2 3 4 5 6 7 8
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Author
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Topic: What AM tower is this (Paul G. Thompson or anyone?)
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Jack Ondracek
Film God
Posts: 2348
From: Port Orchard, WA, USA
Registered: Oct 2002
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posted 10-15-2003 12:40 AM
quote:
Before I got out of radio (about 4 years ago), I found that transmitter sites were becoming poorly maintained at many stations thanks to deregulation. Without the requirement for a FCC licensed tech, any Joe Blow could work on a transmiiter (and a lot of sites I saw looked like it).
Edward, I noticed something very contradictory when I was doing engineering work in Portland, OR.
You would think that a well-maintained transmitter, housed in a climate-controlled, room with good filtering, plenty of air flow & appropriate security would perform well.
In one building, there were 7 FM transmitters. Several of them were maintained just this way... maybe even overdone... those guys were always tinkering with them.
Then... there was the main transmitter combo for what was then the local beautiful music station (and the owner of the transmitter building). The engineer was (and maybe still is) one of Portland's real engineering geniuses. He could probably design just about any kind of site you could imagine... right off the top of his head. But then... there was this transmitter site of his. The transmitter was absolutely filthy looking. Considering that beautiful music was generally the the top-billing FM format at the time, it was almost unnerving to see. Here was a real money-maker in a fair-sized market... running on a transmitter that looked like hell... surrounded on two floors by several transmitter combos of the same 20 year-old vintage that looked like they just came off the factory floor. It seemed really nuts...
until you got to understand the chief engineer's philosophy...
His practice was to leave well-enough alone, period. The transmitters were in the basement of the building, located on top of one of Portland's "mountains", and nobody ever saw the stuff but other engineers. He just didn't see any value in spending time on visual niceties. When his maintenance schedule indicated it was time to change the tubes, he did so... ALL of them. He also replaced the finger stock on the tube sockets, thoroughly cleaned the trombone in the combiner... literally replaced anything and everything that looked like it might need attention of any sort. Then, he turned it on, left the building and other than the required visits to coordinate the meters with the remote control & make sure the whole thing was really still there, he literally ignored it until it was time for the next cycle. The fact that he NEVER took a bottle of cleaner to the outside cabinets or changed any indicator lamps (it was remote controlled, after all) made this machine look absolutely disastrous. His opinion... valid, as far as it goes, was that the condition of the outside surfaces had very little to do with the internal workings... after all... listeners, advertisers and station staff and management never even saw the thing.
But.... it was the most reliable transmitter in the entire market, and there were a LOT of those RCA BTA-20/40 combos in that town. This thing almost NEVER failed, and it was on all the time... NO maintenance shutdowns (the studio was automated, so what the heck).
Sometimes, you just can't tell by looking at the surface of things... go figure!
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Luciano Brigite
Master Film Handler
Posts: 277
From: Sao Paulo, SP, Brazil
Registered: Jan 2002
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posted 10-15-2003 01:02 PM
833! I did see a few of them several years ago at the same place I got the TB I used to make the lamp..I almost got it instead of the TB but because the way it has the pins at the bottom I left them there, It's plate looked very different, with large ceramic suports inside and were made by Philips. it must be a triode and triodes are the fine thing for audio amps .Seeing the data for them makes me wonder the size of the output transformer for a pair of them ![[Eek!]](eek.gif) If wasn't the cost of such parts, I'd give a try at one ![[Big Grin]](biggrin.gif)
Josh, is that tube you're holding a tetrode? ( I know that the coding on them tells what they are but I don't remember then anymore) and goldish cooling fins and anode cap? that I never see. umm lemme try.. 4CX15.000 .. tetrode, ceramic envelope 15.000watts output ? wish I had kept the lousy photocopy of a Eimac catalog someone gave me along with a 3CX2500A3, unfortunately the tube fell from the bench and the rest is well know ![[Frown]](frown.gif)
I'm trying to remember what tube was one of the few xmiter tubes I had that has the grid connection on the side , anode on top and filment on a 4 pin round socket at the bottom ,the tube being about the size of a beer bottle. it's 8?? ( not sure if 813, 811 I think the 813 is a tetrode or pentode)
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Paul G. Thompson
The Weenie Man
Posts: 4718
From: Mount Vernon WA USA
Registered: Nov 2000
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posted 10-15-2003 02:46 PM
Josh, the 4CX15000 you have in your paws look like the 3CX-10000 I use in the Collins. It does look a little like a mushroom with cookie jar handles. ![[Smile]](smile.gif)
Remember we were talking about the 6697 Power Amps in the RCA BTH-50H1 transmitter looking like someone sitting on a toilet? Well, here is a picture from the manual.
That transmitter has balls!
When they fire and it is the first time you ever heard them fire, you'll want to go home and change your underwar.
Of course, I just gotta post a picture of that big pig.
For the test of you engineers out there, here is a little write up on the RCA Ampliphase transmitter:
The principle of Ampliphase is to take a single frequency source, split it into two feeds, phase modulate each feed, then add the two signals in a combining network. Amplitude modulation is achieved by the degree of addition or subtraction due to the phase difference between the the two signals. All (?) Ampliphase transmitters are arranged so that under zero modulation conditions, the quiescent phase difference is 135 degrees. The two signals are modulated in equal but opposite directions by a total of +/- 45 degrees, giving maximum and minimum differences of 180 and 90 degrees. At 180 degrees, the two waves cancel out in the combining network, hence this is the 100% peak negative modulation condition. At 90 degrees, the two waves add to give close to 100% positive modulation.
Ampliphase transmitters quickly acquired the nickname of "Amplifuzz" due to the quirky nature of setting them up and maintaining consistant performance, and became the transmitters engineers loved to hate. (That was definately said correctly. I hated them.)
Although the technique became obsolete for broadcast use in the 1970's, outphasing has undergone a bit of a renaissance in recent years in the microwave spectrum. It is used as an efficient and accurate means of producing phase/amplitude (QUAM) modulated wideband carriers, necessitated by todays digital communications systems.
I just found this out: The 6697 PA is basically no longer available. Not too many companies rebuild them anymore. The tube crosses to nothing. One company I found does rebuild them at about 2800 bucks a pop with a dud. Without a dud, it is 3500 bucks.
I guess the old RCA Ampliphase transmitters that use that tube are going to soon wind up in the scrap yard or serve as anchors for the navy-issue aircraft carriers. EXCELLENT!! The sooner the better.
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Luciano Brigite
Master Film Handler
Posts: 277
From: Sao Paulo, SP, Brazil
Registered: Jan 2002
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posted 10-15-2003 07:45 PM
Phill, all glass tubes does looks better than the glass/metal or ceramic metal tubes and looks even better when running but I remember of one, but not it's code, that was a glass/metal tube about the same size in heigh and 1 1/2 the diameter of a beer can, it had external fins for air cooling that I did like, the curious thing on them.. all the ones I saw, about 20 of them, had the glass part popped off of the metal and you could pull the entire filament /grid assembly out of it.
After staring at the picture of the 833 and reading Paul's post, I started thinking about building a more serious tube amp, i've seen from time to time one or another schematic floating on the net of amplifiers using transmitter tubes in the output stage but never got interested enough to pick one and see what happens.
last one I saw had a ceramic/metal tube as single end class A amplifier. the tube looks cute , if I reall (part of ) it right, it was a 3CX tube made by Svetlana , the most expense on that amp I believe that was the tube itself and the socket .
Now I have one question..
suposing I get to build a more serious amp, using transmitter tubes for output stage ,wich ones I'd give a try?
things to take into account: tube prices, easy to find, sockets and that they're triodes ( to keep some of it simple)
what do you guys says?
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