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In Reply to: Because it is flawed thinking. posted by JLH on March 19, 2007 at 06:45:33:
Would you believe that the cathode FB design at least as implemented by PJ walker in the QUAD II (and as discussed in the polite rant by Mr.’s Walker and Williamson in the link you provided) is usually considered a form of UL. In the QII, g2 is ostensibly a fixed voltage. However, because the output tube cathodes go to ground thru a centertapped winding, there is signal voltage at each cathode. With g2 fixed but cathode voltage changing, it’s effectively the same as if the cathode voltage was fixed but g2 was changing in same magnitude but in opposite direction of cathode. IOW, a corrective feedback signal appears at g2 just like “conventional†UL using taps off the plate windings. There will also be what amounts to corrective feedback at g1 for same reason.One advantage of cathode type UL is that you get to pick your g2 static voltage. You can do this with UL too but it requires an OPT with a separate g2 winding...not all that common. Come to think of it the QII OPT config isn’t all that common either.
One conclusion is that conceptually, UL may not be any more flawed than other feedback schemes. However, since proper implementation seems to require a very good OPT, practical implementations may indeed be flawed to some degree when cost is a major consideration.
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Follow Ups
- Re: Because it is flawed thinking. Well maybe not so flawed... - Steve O 12:10:26 03/19/07 (2)
- Re: Because it is flawed thinking. Well maybe not so flawed... - JLH 18:15:10 03/19/07 (1)
- Re: Because it is flawed thinking. Well maybe not so flawed... - Steve O 20:07:16 03/19/07 (0)
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