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RCA TRANSMITTERS (TT10AH, TT25BH) |
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RCA TT-10AH TRANSMITTER :
TEN CABINETS.
RCA TT-10AH and TT-25BH Transmitters
"Alternate", "Backup"
Picture about 1993
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This transmitter is the back up, and is used if the primary fails.
This old transmitter was the first model of television transmitter produced by RCA. In fact, this
transmitter was originally a monochrome (black and white) transmitter, until modified for color.
The transmitter utilizes a 6166 tube.
But, do NOT be deceived; this transmitter has advantages:
It has a great picture; almost as good as the primary.
This hardy transmitter tolerates lightning,
and PGE surges, that the solid-state primary can not sustain. This transmitter is rugged.
THE BACK of a RCA TT-10AH TRANSMITTER:
Picture about 1993
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Shown are about seven of the ten cabinets.
All back doors are safety interlocked: If a door is opened, then the high voltages will be removed,
and also all high voltages will be shorted to ground. Once broadcasting begins, the doors should
not be opened; all transmissions will emmediatly cease if any door so much as - slightly - comes adjar.
POWER AMPLIFIERS (RCA TT25BH)
The Alternate visual transmitter(RCA TT-10AH) needs to be followed by two of these POWER AMPLIFIERS (or
PA's). Each produces about 18 kw, and combined produce about 37kw peak power.
Each amplifier is class "AB" with seven 5742 tubes in parallel. The tuning controls are moved by motors, gears, and chains.
2001
PA on the right
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As a side note...
The PA's tuning controls almost came under the eye and the hand of my autonomous system.
But automation work would have been probably waisted due to the unreliable tuning motors.
It takes several nights to tune the two PA's by hand. But the motors and gears are troublesum in that chains jump over sprocket teeth, and sliding finger stock binds. It is chronic and hopeless,
and definitely requires the human touch. My system controled the basic operation of the Power-Amplifiers, but not tuning.
Sitting on top of each PA is a chimney made of corrugated fiberglass pannaling. The paneling channels the heat completely into the attic. Even with all PA heat diverted to the outside, there is
enough heat remaining to warm the entire building.
The two power amplifiers are RCA model TT-25BH.
There are external two cabinets associated with each PA:
Shown here are a control cabinet and a high voltage cabinet. The control cabinet is shown with the
door open. "Cosmetic" doors are not interlocked, and include most front doors.
However the cabinet to the right is interlocked; It contains 6,000 volts!
All cabinets contain viewing windows.
Normal blue-green glow from mercury vapor rectifiers is a normal site.
PA-A is putting out more than 100% power because PA-B is putting out less than 100%. The two PA's are combined forming a sort of average for the final power. What powers are not matched are
rejected into a load: called a reject-load.
SIDEBAND FILTER ROOM : 
After the signal leaves the two PA's, it
goes into the sideband filter room. The Vestigial Side Band Filter is composed of six large copper "cans".
These cans form tuned cavities, or tanks, to reduce the lower sideband.
The cavities are
forced air-cooled.
Their temperature is determined by how efficiently the two PA's are tuned:
the more lower side band content; the hotter the filters.
Modern transmitter manufacturers no longer
have to forgo the expense of copper and silver cans.
(To give an idea of scale, there is an operator standing behind the last filter.)
Transmitters, such as the primary, still utilize sideband
filtering, but now use a very small - low-level - acoustic-wave filter.
REMOVED TRANSMITTER RF PATH AND RADIATION