NO you didn't miss a trick.
Its just a Gingertube stuffup - blazed off a response without really thinking too hard about it (not hard enough anyway).
Now that I AM thinking about it - this is not going to work. The 2 anodes of tyhe diff amp will end up sitting about 1V away from Rail voltage and so won't be able to swing any signal.
Hey - I'm a professional design engineer so I can say with confidence I now know one more way how NOT to do it.
Cheers,
Ian
Its just a Gingertube stuffup - blazed off a response without really thinking too hard about it (not hard enough anyway).
Now that I AM thinking about it - this is not going to work. The 2 anodes of tyhe diff amp will end up sitting about 1V away from Rail voltage and so won't be able to swing any signal.
Hey - I'm a professional design engineer so I can say with confidence I now know one more way how NOT to do it.
Cheers,
Ian
Hi, KenPeter,
Not really, ut's only a 6SL7 LTP followed by a 6SN7 diff amp. With the CCS plate loads paralleled by 2.2 Meg, though, gain is almost as high as you can get it - close to mu.
Glad you could get it working. I should havr included the single channel stand-alone circuit - please see attached.
No, it's a trick to check damping factor. I activate the 1v source to see how close to 1v it can get across the speaker - the higher the better. This circuit manages 0.9v, which means a DF of about 9. Please see spreadsheet contained in the attached zip file.
Not really, ut's only a 6SL7 LTP followed by a 6SN7 diff amp. With the CCS plate loads paralleled by 2.2 Meg, though, gain is almost as high as you can get it - close to mu.
Definitely!
Hi Ian,
It doesn't have to be done the way I modeled. You can instead set the plate CCSs to draw more current between them than the cathode CCS, and use bypass resistors from plates to ground instead of plates to B+. You can still select the resistors (or, better, the amount of current imbalance) to get the plate voltages to be what you need them to be.
Must always allow enough headroom for the required swing, of course, whichever way you do it.
I didn't think you were serious about current mirrors but I agreed that there was no need to use poor CCS's as the plate loads once you decide to build in a deliberate current imbalance.
It doesn't have to be done the way I modeled. You can instead set the plate CCSs to draw more current between them than the cathode CCS, and use bypass resistors from plates to ground instead of plates to B+. You can still select the resistors (or, better, the amount of current imbalance) to get the plate voltages to be what you need them to be.
Must always allow enough headroom for the required swing, of course, whichever way you do it.
I'd just like to add that the balance between CCSs is quite fine - that's what the resistors in parallel with the source resistors are for, "fine tuning". I would have some doubts that they would stay in equilibrium over the long term. Modeling these types of circuits is fun and shows what can be achieved, at least in theory, but I suspect that actually building and using them is a different kettle of fish and I doubt if I would go to those lengths. YMMV
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