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That's true. I worked at an ABC affiliate in the 70's and they were using a converted B/W transmitter (TT25BL). I saw the manual for the retrofit and basically it replaced the ENTIRE modulator panel. It was about 20 inches high and 16 inches wide and had more tubes. Transmitters were high level modulated back then and it took about 200 Watts to modulate to 100% (grid modulation).
The TT25EL was built for color and the station across town had one of those. But it was high level modulation too.
In '77 we installed a Harris BT25L2 which, as I recall, was the first low level modulated transmitter. It used a transversal sideband filter, at an IF frequency, which was a sort of SAW filter.
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