It's just one point on the Eg1=-1V curve for reference purpose, not a recommended operating condition ...
+1.
Look at the Philips data sheet Kagliostro linked in the 1st post. Scroll down to the plate curves on the 6th page, then look at the -1v gridline. That line has a point at about 285mA and 60v plate-to-cathode.
I think the confusing chart is showing a single data point of max power output (-1v is commonly held as a safe grid voltage prior to the onset of grid current and serious distortion) which is at the knee of the curve and tell you peak plate current, plate saturation voltage, and allows you to calculate the plate load impedance needed for your proposed supply voltage.
It also hints at that supply voltage (more than the 210v on G2) and shows the maximum screen current at that moment of peak plate current.
The sheet says max voltage is 250v, so the total peak voltage could be as much as 250v-60v = 190v. The 285mA peak current is given by the chart and graph, when the grid is driven by a peak positive input signal to momentarily reach -1v. Taken together, this implies a power output in class AB of (190v*0.285A)/2 = ~54w/2 = ~27w, when there is a load of 4 * (190v/0.285A) = 4 * ~670Ω = ~2700Ω plate-to-plate.
The load seems low and the power output seems hopeful for such a small glass bulb. I'd guess the realistic output is less than 27w for a pair but more than 1/2 that, and that a higher load impedance would be needed for audio use. The very high peak current possible seems more realistic in a pulsed-operation setting, as suggested by the data sheet's note this is a frame oscillator or pulse-amplifier tube.
For example, a 5kΩ load for class AB yields (for the same 250v plate and 60v plate saturation) 190v/1.25kΩ = 0.152A and (190v * 0.152A)/2 = ~14.5w. May or may not be all this tube could deliver, but more refinement would take more than back-of-napkin figuring.
The dynamic characteristic on page 5 of the Philips sheet implies the tube's Gm. For the G2=210v curve, the points of 100mA and 200mA of plate current coincide with grid voltages of -15v and -8v for a Gm of (200mA-100mA)/(15v-8v) = 100mA/7v = ~14.3mA/v. The 152mA of peak current for our 5kΩ plate-to-plate load case then requires 152mA/14.3mA = 10.6v of peak input. Leaving at least 1v extra to stay away from grid current, this suggests a bias voltage of at least -12v.
Adventuresome tinkerers might try biasing cooler and pushing the load lower, but that might be best figured out experimentally.
Topic: This tube is really odd - B+ 65v - G2 210v ????? (Read 3058 times)