Damage Control

[jshorva65]

In addition to the thread about Safety, some attention should also be given to prevention of damage to the sets during the restoration process. It was common practice among the old-timers in the repair business, for example, to disable the HV during RF/IF alignment. There are good reasons for doing this besides the obvious prevention of HV shocks. Arcing can occur and result in damage to the HV supply circuits. To disable HV, I recommend these procedues.

Pre-War Sets:

Do not merely remove the HV rectifier tube, instead you should disconnect the primary winding of the HV transformer from its supply to eliminate all HV. Most pre-war sets used a separate transformer to develop HV.

Post-War Sets, Magnetic Sweep:

Even if the service literature says that it's ok to disable the HV by removing the Horiz Osc tube, don't do it. This line in the adjustment procedure is based on the assumption that the set's power supply is furnishing the correct grid bias to the Horiz Output tube and will limit its plate current to a safe value. If this bias fails, the tube will overheat damaging itself and possibly the flyback transformer. Do not merely remove the Horiz Output Plate Cap, as the screen grid will still be supplied with B+ and will overload the circuitry which provides screen vltage to the tubeand may also damage the tube. I remove the Horiz Output tube and the Damper Tube from their sockets to disable HV and securely cover the plate cap connector with a piece of insulating tubing. Never operate a color chassis with its H. Out and Damper tubes in place before verifying that the Hor Osc is working correctly. It was common, especially in color sets but also in many BW sets to develop the H. Out tube's bias (which limits plate current) from the Horiz Drive. In the absence of proper Horiz Drive, the output tube will draw excessive current. Serious damage may result.

Post-War Sets, Electrostatic Sweep:

Remove the HV Osc tube which drives the RF HV transformer. This tube may be inside the HV cage or adjacent to it and is normally a power tube of some kind (6K6 or similar).