[Sideband]

I thought it was the grid base (cut-off point) that was the important characteristic? The valve as I understand it is biased near the cut-off point when used as an anode bend detector. The 994V is also good in my 274 but I have tried other valves as well, notably a triode strapped EF80 (what else??) with a doubler for the heater and a resistor to bring the voltage down to 6 volts and a 164V which I happen to have. Both worked after a fashion but gave lower gain than the 994V. They all gave a degree of distortion on strong signals.