NewYorkDave
Well-known member
OK, before PRR nails me on the semantics, I'll point out that it's really two tubes contained in a single envelope. But anyway...
Some of you might remember this idea for a simple tube preamp that I posted some time ago:
I just wanted to bring this up again since I'm getting ready to actually build one of these and see if the real performance agrees with predicted performance. I wanted to mention, for the benefit of anyone else who's thought about building it, that simulation suggests that running the second triode at a higher plate current will improve performance in driving the fairly difficult load. No big surprise there. I don't trust simulations in general, but the 12AV7 model I've been using has proven to be surprisingly accurate with other circuits I've designed, breadboarded and then simulated after-the-fact.
Anyway, try 470-510 ohms in place of the 1K cathode resistor. This will increase plate current by a milliamp or two, with a corresponding drop in plate resistance. The plate will sit at around half the supply voltage--instead of higher than half, as it did before--which will give a greater maximum symmetrical output voltage swing. The open-loop gain stays about the same, so the feedback factor remains the same.
Or at least this is what the simulator is telling me. We'll see... :wink:
Some of you might remember this idea for a simple tube preamp that I posted some time ago:
I just wanted to bring this up again since I'm getting ready to actually build one of these and see if the real performance agrees with predicted performance. I wanted to mention, for the benefit of anyone else who's thought about building it, that simulation suggests that running the second triode at a higher plate current will improve performance in driving the fairly difficult load. No big surprise there. I don't trust simulations in general, but the 12AV7 model I've been using has proven to be surprisingly accurate with other circuits I've designed, breadboarded and then simulated after-the-fact.
Anyway, try 470-510 ohms in place of the 1K cathode resistor. This will increase plate current by a milliamp or two, with a corresponding drop in plate resistance. The plate will sit at around half the supply voltage--instead of higher than half, as it did before--which will give a greater maximum symmetrical output voltage swing. The open-loop gain stays about the same, so the feedback factor remains the same.
Or at least this is what the simulator is telling me. We'll see... :wink: