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RE: Schematic?

The schematic below is one channel of the HK Citation V. The 6CG7 dual triode is configured as a long tailed pair. There are various descriptions of this circuit online that show it in a somewhat more simplified format. The Cit V drives the LTP with a 12BY7 pentode that has quite a bit of gain. Replacing the 6CG7 with a higher gain dual triode, maybe a 12AY7, would allow use of a triode in place of the pentode. If a dual triode was used, half could be in one channel and half in the other. IOW, one bottle would serve as preamp for both channels, and two more bottles for the left and right long tailed pairs. So, a total of three tubes. If one wanted to use 9-pin pentodes as preamps, the number would grow to four tubes. This can provide a highly nuanced driver, particularly if the input pentodes are wired as low distortion triodes. Note that there are only two coupling caps in the HK circuit, and that it has both AC and DC balance pots.

The only suitable service for a 12AU7 is cathodyne phase inverter or cathode follower, both of which take advantage of the inherent feedback of the circuit to linearize the tube. As a grounded cathode gain stage, the 12AU7 has no place in hi-fi, and it has only ever been useful because an abundance of negative feedback around the tube can mask some of the ills. That's no way to design equipment considering the superb tools and components that are available now.

















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