12FQ7

The 12FQ7 is a medium-mu miniature twin triode in the 6FQ7/6CG7 family. RCA’s manual describes these tubes as combined vertical- and horizontal-deflection oscillators in color and monochrome television receivers, but also refers to resistance-coupled amplifier treatment. The documentation therefore explains both its television role and its two amplifier elements without assigning undocumented uses in particular audio equipment.

The defining difference is the heater: 12FQ7 needs 12.6 V at 300 mA AC or DC, against 6.3 V at 600 mA for 6FQ7/6CG7. RCA’s August 1970 sheet specifies controlled heater warm-up but gives no number of seconds on that page. The manual lists 11 seconds under 6FQ7/6CG7 and leaves 12FQ7 blank, so that figure must not automatically transfer. Its nine-contact miniature base uses diagram 9LP: heater pins 4 and 5, one triode on 6, 7 and 8 and the other on 1, 2 and 3, respectively anode, grid and cathode. Pin 9 is unconnected.

Each section has a stated amplification factor of 20. At 90 V anode and 0 V grid, the manual gives 10 mA anode current, about 6700 Ω internal resistance and 3000 µmho transconductance, or 3 mA/V. The second point, 250 V anode and −8 V grid, gives 9 mA, about 7700 Ω and 2600 µmho, or 2.6 mA/V. The factor 20 is a triode parameter, not guaranteed gain for any stage: circuit and load determine actual gain.

RCA’s general design-maximum limits are 330 V anode and 22 mA cathode current. Dissipation is 4 W for either anode but 5.7 W total with both sections operating, so two 4 W dissipation allowances cannot simply be added. Heater-to-cathode limits are ±200 V peak and 100 V average; maximum grid-circuit resistance for fixed bias is 1 MΩ.

For special oscillator operation in 525-line, 30-frame television systems, RCA further distinguishes vertical from horizontal service, with their own pulse limits. Those values do not replace general amplifier conditions. Interelectrode capacitances are also separate: grid-to-anode capacitance is about 3.6 pF for one section and 3.8 pF for the other. Distinguishing the units, continuous from pulse operation and heater supplies is essential when reading this family’s data.