From FB group Building Transistor Radios 2018-10-26
I repaired a lot of old tube TVs, and I saw that the repairs were dying when it was cheaper to remove the chassis from the old TV’s beautiful wood cabinet and buy a new cheap TV and put it into the wood cabinet. It even had a remote control.
I remember that one sweep generator, Vertical (I think), was difficult to keep locked (the picture would roll) if the resonant circuit in the sweep gen was not working. Without it the sweep gen made a sawtooth wave, and the sawtooth top was broad, so the sync could lock on to a wide part of the sawtooth, and cause instability. The resonant circuit adds an ‘S’ curve to the sawtooth wave, so it has a sharper point and the sync locks on to that sharp point, making the picture stable.
I found that one big problem with the tube TVs was they changed the vertical sweep circuit to use a PC board. The heat from the tube would turn the light brown PC board dark, and as it got older and darker more of the PC board turned to carbon. The vertical circuit used high resistances, and the carbon in the PC board would start to shunt the current away from those high resistances and the vertical sweep would stop working properly. I could swap everything but the PC board and the circuit still would not work. It cost more to replace the PC board than to buy a new cheap TV from Panasonic! I saw that it was time to quit repairing consumer electronics.
