Posted by Lew on May 22, 2004 at 11:07:21:
In Reply to: Dear Lew - 6c33c tube posted by Matt Rogers on May 22, 2004 at 00:26:10:
I could not really tell you about the "sound" of the 6C33C as compared to any other tube you might want to use in the circlotron output stage, because I never have heard any of the standard Atma-sphere amps (which all utilize the 6AS7, as you know) in my system. I can only say that since I built my amps (using MA2-type chassis', power transformers, etc.), I have been able to hear clearly each step-wise upgrade of the input circuit and power supplies that I have incorporated. This includes (1) converting from the original 12AT7-based input circuit to one utilizing 6900s and ECC99s, (2) upgrading coupling caps to teflon, (3) adding pi filters to the B+ and B- hi-voltage power supplies, (4) adding Paul Speltz's CRCRC mod to the low-voltage supplies for the output stage, (5) adding LC circuits to isolate the bias supply, B- , and B+ from each other, (6) adding constant current sources to the driver stage tubes (now 12SX7s), (7) removal of all zener diodes from the circuit. So the 6C33Cs are "transparent" enough to enable me to appreciate the tweaks.