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PCC84 / 7AN7

From The Radio Constructor, May, 1954.
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This double triode with separate cathodes and internal shielding between units has the high slope of 6 mA/V at the low anode voltage of 90 Volts which is required to obtain optimum performance from the DC cascode RF amplifier used to achieve adequate signal-noise ratio. The use of cathode bias for the grounded cathode triode not only minimises variation of the input impedance with AGC but also extends the cut-off. This permits cross-modulation to be kept to a negligible level without resorting to a remote cut-off valve, which would affect adversely the signal-noise ratio by increasing the damping of the input circuit or by reduction of the gm. Minimum noise can be obtained, Whilst maintaining low input damping, by strapping the two cathode leads of the input triode.

With a 0.3 Amp heater, this valve may be used in AC/DC equipment.

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