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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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Tube DIY Asylum Do It Yourself (DIY) paradise for tube and SET project builders. |
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In Reply to: Is It Possible? posted by FlaCharlie on August 7, 2007 at 10:34:11:
Charlie, here's a sample loadline analysis using a 6SN7's to drive 6B4's. The assumptions that I've made are that the 6B4's are biased with about -45V on their grids (relative to the cathodes) and that a supply of about 300V is available for the 6SN7's
The loadline in red is 47k ohms. One end is at the supply voltage of 300V and the other end is at 300/47k = 6.4mA. I chose an operating point of 3.5mA which puts the plate of the tube at about 135V. That's indicated in blue. The difference between supply and plate voltage (300-135=165V) is dropped across the 47k plate resistor. It all checks out with Ohm's Law: V=I*R=0.0035*47000=164.5. Close enough...
Green indicates the part of the loadline that will be traversed when driving the 6B4's to full power. Since the 6B4's are biased at -45V the plates of the 6SN7's will need to swing +/- 45V peak. The quiescent plate voltage is 135V, it will need to swing up 45 to 180V and down 45V to 90V. What is also shown in green, but is hard to see, are the corresponding 6SN7 grid voltages (really, grid to cathode voltages.) Just reading them off the graph, the quiescent grid voltage is about -4.5 and it needs to swing between about -1.9 and - 7.5 to drive the 6B4's fully.
Ok, that means you'll need about 3 volts peak input to the 6SN7, or twice that at about 6 volts peak is they are configured as a LTP. If you have a preamp that can deliver that, then you're golden. If you don't need full power, then you might get along just fine with less input signal.
-- Dave
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Follow Ups
- RE: Is It Possible? - Dave Cigna 08/8/0709:03:19 08/8/07 (0)
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