6CB6

The 6CB6 is a sharp-cutoff miniature pentode developed for radio-frequency and intermediate-frequency amplification. Tung-Sol specifies it particularly for IF stages above 20 MHz and for RF amplifiers in VHF television tuners; Mazda Belvu documentation confirms RF amplifier service. The tube has an indirectly heated cathode, a 6.3 V, 300 mA heater that can run on AC or DC, and a seven-pin miniature base. In the RCA pin arrangement, the suppressor grid and internal shield share pin 7.

At high frequencies, unwanted coupling between the control grid and plate also matters. RCA gives a grid-to-plate capacitance no greater than 0.020 pF without an external shield and 0.010 pF with the specified external shield connected to the cathode; these values belong to its measurement conditions, not a guaranteed improvement in every installation. Published operating points differ: RCA typically gives 200 V on the plate, 150 V on the screen grid, a 180 Ω cathode resistor, 9.5 mA plate current and 6,200 µS transconductance. Tung-Sol, at 125 V on both plate and screen, gives 13 mA and 8,000 µS. These are different conditions and their results must not be combined.

The sheets also use different rating systems. Under its design-center system, RCA gives a maximum of 300 V on the plate and 2 W plate dissipation; under its design-maximum system, Tung-Sol gives 330 V and 2.3 W respectively. Both distinguish screen supply voltage from the voltage actually present on the grid. Tung-Sol lists the 6CB6 beside the 6CB6A and specifies that the latter has controlled heater warm-up to reduce voltage surges in a suitable series heater chain: this difference should be checked when considering a replacement in a television set.