Posted by TubeCraft [ 207.106.24.98 ] on January 10, 2005 at 15:12:45:
In Reply to: Grounded Grid posted by Poindexter on January 09, 2005 at 13:26:39:
Rosenblit may have designed this particular preamp, but the circuit has been around for many years. You can read all about it in the circuit guide at the Tubecad website. John Broskie refers to it as a "common cathode" circuit - if you look hard enough, there's a favorable evaluation of Rosenblit version there as well. It's two triodes with the cathodes tied together, hence the name "common cathode" - only the second triode is a real "grounded grid" - the first triode is really a cathode follower. The cathode follower drives the grounded grid.
Not many home audio components could drive a grounded grid circuit directly - typical input impedance of 600R - or less.
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