6CS6

The 6CS6 is a miniature dual-control heptode designed chiefly for television synchronizing circuits. General Electric describes it as a combined sync separator and sync clipper; Tung-Sol notes that its construction improves noise immunity in a separator. Both control grids, the first and the third, have sharp-cutoff characteristics. This dual control input, rather than the electrode count alone, explains its use in circuits that must distinguish useful sync pulses from unwanted signals.

The valve has an indirectly heated oxide-coated cathode and a 6.3 V, 0.3 A heater that can be powered by AC or DC. It uses a seven-pin miniature E7-1 base with the 7CH pin arrangement: grid 1 is on pin 1, grid 3 on pin 7, the interconnected screen grids 2 and 4 on pin 6, the plate on pin 5, the cathode and grid 5 on pin 2, and the heater on pins 3 and 4. The RCA manual lists the 3CS6, 4CS6 and 12CS6 alongside the 6CS6 as types with identical electronic characteristics apart from their heaters; a replacement therefore requires checking the heater circuit's voltage and current.

An operating point given by GE, Tung-Sol and RCA for separator and clipper service uses 10 V on the plate and 30 V on the screen grids, with both control grids at 0 V. Typical plate current is 2.0 mA and screen current 4.5 mA. The sheets then show that the two control grids do not have the same effect under every condition: at 100 V on the plate and 30 V on the screens, biasing grid 3 to −1 V with grid 1 at 0 V gives 0.8 mA plate current; biasing grid 1 to −1 V with grid 3 at 0 V instead gives 1.0 mA. These are separate tests, not values to add together.

The sheets set the plate-voltage limit at 300 V and maximum plate dissipation at 1 W; they also give 14 mA as maximum DC cathode current. The screen-grid figures need closer reading: GE distinguishes a 300 V supply-voltage limit from a 100 V limit on actual screen voltage; RCA and Tung-Sol give a 300 V supply limit and refer permissible actual voltage and dissipation under different conditions to rating charts. One detail on which the sources differ is the maximum grid-1-to-plate capacitance, measured without an external shield: GE and RCA give 0.07 pF, Tung-Sol 0.05 pF. The documentary differences remain attributed to their respective sheets. Documentary sources: 6CS6 sheets from General Electric, Tung-Sol and RCA; RCA Receiving Tube Manual.