Your bias calculation is correct but doesn't factor screen current.Ī bias probe also won't tell you if the plate dissipation is low, but the screen is drawing excessive current through a fault condition. A bias probe will always over-read compared to (say) the transformer method. All of the current through the tube is being measured at this point and includes screen current as well as plate current. If you use a bias probe you're measuring the cathode current. If I bias to 25mA and +B is 400V, the dissipation is 400X0.025=10W. When you say 70%, do you calculate the plate current times the plate voltage? Like for 6V6GT that is spec for 12W. You would think it's a cake walk to build such a simple thing, WRONG!!! I had to scramble to get a combination of resistors to get the 1ohm. I giggle the resistor so much I broke the lead of the resistor. But it took me a long time to realize that because unless you have a X-Ray eye, you can't see the inside where it got stuck. Turn out the posts from the top socket bottomed out. Instruction is not good, the two parts just don't fit tight. Actually I just finished building the bias probe from a kit bought in Tube Depot. I do use a bias probe, not just the voltage. Both those are fairly cool 6L6 number to a 70% guy.Is the wattage for a single 6L6? What is the formula for calculate output power? So if that results in Cool 6V6 versus hot 6L6, so be it.Īt 440v B+ 33ma yields 14 watts, and 39ma yields 17 watts.
After all, once you make an amp, you won t be setting it to an arbitrary, sake-of-argument idle current, you will be setting it to its best sound. If you want to pick a tube to design an amp around, let me suggest tune each tube to its best sound, then compare THAT. Both those are fairly cool 6L6 number to a 70% guy. Bias voltage is not standardized, you just set it to whatever gives you the target performance current.Īt 440v B+ 33ma yields 14 watts, and 39ma yields 17 watts. Your current versus bias voltage numbers will vary tube to tube. On the other end, a gain monster amp like a Peavey 5150 comes stock at between 20-25% dissipation. But of course there are 80% guys and 60% guys. other guys like the 70% dissipation rule of thumb. I think it sucks for guitar amp, but some guys adjust bias to eliminate crossover notches - the hifi approach. Normal speed for 8 cylinders? Normal speed for 6 cylinders? That is like asking what is the normal speed for a car. As far as I know, any current production 5881 is just a 6L6.
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