PCL85

The PCL85 is a triode-pentode for a television set's vertical-deflection stage. Philips sheets assign the triode to the frame oscillator or pulse amplification and the pentode to frame output. The two systems have separate cathodes and are housed in an envelope with a noval base. Technical documentation relates the PCL85 to the ECL85 in the characteristics of their electron systems, but clearly distinguishes their heaters: the PCL85 is intended for a 300 mA series heater string, whereas the ECL85 uses a 6.3 V parallel heater supply.

The pentode's operating conditions concern a deflection waveform, not a constant plate current. Philips gives examples with 50 or 65 V at the plate, respectively 170 or 210 V at the screen grid, and peak plate currents of 200 or 285 mA. In its later PCL85/PCL805 sheet, Philips gives up to 2 kV as peak plate voltage and 75 mA as the average cathode-current limit. The peak voltage is permitted only for pulses lasting no more than 5% of a cycle and 1 ms: it is not a continuous operating voltage. For the triode, the same documentation gives separate operating points at 100 V plate voltage, showing that this section too must be assessed in its circuit.

The consulted sheets agree on a 300 mA heater current but give slightly different voltages. A 1961 Philips sheet, a La Radiotechnique note and a technical catalogue give 18 V; later Philips and Mazda sheets give 17.5 V. The documents examined do not explicitly attribute this difference to a construction change. When restoring a television set with a series heater string, the sheet for the actual specimen and the voltage drop intended by the circuit should therefore be checked, rather than assuming that 17.5 and 18 V are automatically interchangeable.