Your knowledge of tubes doesn't sound all that crazy to me. But someone may commit you to a straitjacket for believing you have Martian speakers.
..Todd
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Sorry, I've been away for a few days.
If you want to balance up the phase splitter then, assuming the current resistor values are reasonably accurate, it is the lower 270K which needs to be increased. You are not adjusting a circuit which is already nominally balanced (which could need trimming on either side) but creating balance in a circuit which is currently unbalanced because the phase splitter triode has insufficient gain - you need infinite gain to get balanced output from identical resistors! The 47K resistor to ground adds further loading, so reduces the loop gain seen by the 'error signal' generated at the junction of the 270K resistors. You can't increase the 47K by much, as this also provides grid bias for the output. Some versions of this circuit separate the feedback and grid bias functions into separate resistors - more components, but potentially better balance.
Unlike other phase splitters, this one simply inserts an extra stage into one phase; this extra stage should have a gain of exactly -1. Negative feedback is not magic. To get -1 you either need an op-amp instead of a triode, or to modify the resistors.
Of course, a separate question is "how much balance do you need?" Lack of balance means that the second-order distortion in the output stage is not fully cancelled - some might like this as it would add a little SE flavour.
If you want to balance up the phase splitter then, assuming the current resistor values are reasonably accurate, it is the lower 270K which needs to be increased. You are not adjusting a circuit which is already nominally balanced (which could need trimming on either side) but creating balance in a circuit which is currently unbalanced because the phase splitter triode has insufficient gain - you need infinite gain to get balanced output from identical resistors! The 47K resistor to ground adds further loading, so reduces the loop gain seen by the 'error signal' generated at the junction of the 270K resistors. You can't increase the 47K by much, as this also provides grid bias for the output. Some versions of this circuit separate the feedback and grid bias functions into separate resistors - more components, but potentially better balance.
Unlike other phase splitters, this one simply inserts an extra stage into one phase; this extra stage should have a gain of exactly -1. Negative feedback is not magic. To get -1 you either need an op-amp instead of a triode, or to modify the resistors.
Of course, a separate question is "how much balance do you need?" Lack of balance means that the second-order distortion in the output stage is not fully cancelled - some might like this as it would add a little SE flavour.
Hello All!
I wonder if anyone knows what happen to Cassiel? I was chatting with him several years ago about the splitter above- topology and exact values are taken from Leben amplfier, but I do not know the HT voltage. In original design it is probably abput 200V. Can anybody help me with this ? Thank You
I wonder if anyone knows what happen to Cassiel? I was chatting with him several years ago about the splitter above- topology and exact values are taken from Leben amplfier, but I do not know the HT voltage. In original design it is probably abput 200V. Can anybody help me with this ? Thank You
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