WGSF Television

Link: http://wgsf.oldgleaner.com/

The original equipment used at WGSF was built in the heyday of the vacuum tube, following in a long tradition of both broadcast and consumer equipment. Practically every piece of equipment used them, lots and lots of vacuum tubes. Cousins to the light bulb, with many of the same characteristics: they weakened with age, and often departed this useful life by “burning out,” that is, the heater or filament opened. Of course, they could also develop a short between the elements in the tube, sometimes taking out several other components as well.
Most broadcasters - and industrial users of vacuum tubes - tried to head off such disasters through “Preventative Maintenance.” That is, we periodically checked or measured the quality of the tubes. Time consuming, yes, it meant pulling out each vacuum tube in turn, usually with the equipment turned off, dialing up the tube characteristic on a roll chart on the tube checker, inserting the tube, allowing time for it to “warm up,” and pressing the test button. The reading was duly noted and recorded on a chart listing each tube, the equipment location, date, etc. Those that failed to measure up were replaced from the spare stock. We were required to maintain sufficient spares to restore operation in case of an outage.
Most of the vacuum tubes were similar to those used in countless radio and television receivers all over town. We could obtain these at one of two dealers in town, and were given quantity discounts, the same as radio and TV repair shops.
Other tubes were more specialized, especially those used in the power stages of the transmitter. Industrial types, like 5763, 829B, 4X150, 866A and 872. We went to an industrial tube dealer in Columbus for those. The price was still reasonable, but the “biggie” was the GL-6942 transmitting tube. Made only by General Electric, the manufacturer of the WGSF transmitter, a trip to the store hit the supply fund hard. Always above $1,000, they were going for about $1,600 - each - by the mid 1970’s, and the transmitter used two of them.
The Gl-6942 was a specialized power tube, designed for use in a coaxial cavity at UHF frequencies. It required a specialized turn-on and warm up procedure, blower cooling at all times it was powered on, and gradual cool down. Still, a filament or inter-electode short took out more tubes than old age. Replacing a final tube also required a lengthy retuning process - no two tubes were ever exactly alike - electronically.
The transmitter was not the only equipment to require kilo-buck expenditures for tube replacement. The television cameras had their equivalent in the photo pickup tube, the image orthicon, or I.O. Though not subject to shorting like the transmitter finals, these tubes had their own quirks. As they aged, the tubes would tend to retain the image focused upon the photo mosaic. They became “sticky.” It helped if you could “orbit” the image, that is, you slowly moved the camera just a little bit to the right, then up, then left, then down, over and over, trying not to jerk or be readily noticeable to the audience. It took practice to become a good “orbiter.” Electronic orbiters were eventually developed, and were included in the units in the mobile truck when we got it. Still, the time came when replacement was a necessity. We would hold out as long as possible, then cough up the $1,200 to $1,600 price tag, and enjoy a new, non-sticky tube - for a while.
We discovered that we could buy a new videcon type camera for the price of that one tube. Mostly solid-state (transistorized) except for the pick-up videcon tube, and the CRT in the viewfinder. Low power, long lifed, and certainly attractive. Except that the cameras in that price range didn’t meet broadcast video specifications for certain waveform measurements. We found a way around that, though. The TK-30 camera control unit provided the necessary horizontal and vertical drive pulses going to the camera head, and then added the proper sync, blanking, pedestal and shading signals for the return video. We made an adapter that allowed us to connect the GBC Videcon camera to the TK-30 camera control unit. The camera got the necessary synchronizing drive pulses for proper timing, sent the video back to the control unit - which didn’t know that the original TK-30 I.O. camera head wasn't "out there!" We could set the pedestal and gain, and even adjust the shading, all with a substitute camera that cost about the same price as a replacement I.O. tube.
Later, I was able to obtain a small,transistorized rack-mounted unit to replace the TK-30 control unit. The full TK-30 complement went to the Ohio Historical Society when the station ceased operation. By that time, newer camera equipment and video production switchers contained more elaborate circuitry than our racks and boxes of tubes ever had.