ampllifier design

Why do you like those tubes? Any particular brands? Also, what kind of sound are you trying to achieve with your "ampllifier?" Finally, what kind of circuit design do you prefer -- and why? I like the 6922, 6H30 and 6550C. Execution of design probably makes as much difference as the tubes, don't you think?

The 6DJ8/6922 family of tubes, which includes the Russian 6H30 extension, are not designed for audio, and while quite linear, tend to have a microphonic signature that is considerably more pronounced than in other tubes designed for audio, like the 12A* series, 6SN7 or the like. The 6CG7 is the same thing as a 6SN7 but in a miniature style package. It tends to have more microphonics than the 6SN7 does as a result.

Although less efficient, power triodes otherwise will run circles around the best pentode power tubes in every way, including longer life.

If you want to use EL84s as output tubes . . . they're a good candidate for traditional Ultralinear loading, operating class-AB1 with cathode bias - you'll get a solid ten watts with very respectable distortion.

Choice of driver tubes of course depends on the driver circuit topology - you could do it Dyna-style with a pentode driving a split-load phase inverter . . . look at a schematic for a ST-35.

Personally, although I'm a Dyna fan . . . I prefer a long-tailed-pair phase inverter, and it's really hard to improve on a well-implemented 12AX7 or 12AT7 in such an application. For an input tube, if you wanted high loop gain, then an EF86 pentode would work great, and what you end up with is basically a Mullard 5-10 circuit. But for a modern amp (especially if driven from an active preamp), then the gain is not as necessary, so I'd probably use a plain ol' 12AX7, and share it between the both channels. There's a good reason why the 12AX7 is so ubiquitous . . . if correctly implemented, it kicks butt, and it's a reasonable assumption that they will be easily available long after we're all dead.

No matter what you choose, I'm a big advocate of well-implemented feedback amplifiers, and with EL84s, there's no reason why you should need more than two driver stages, and the input stage should be DC coupled to the phase-splitter for minimum phase shift. If well designed, a traditional EL84 amplifier can be of reasonable size and price, good stability, long tube life, good speaker compatability, zero maintainance, low distortion, and very good sound quality.

my reason for selecting the 6cg7, especially tungsol and rca, circa 1960's:

i have found that of the three tube types, 6922, 6dj8 and 6cg7, the latter, in my experience has , subjectively been experienced by me as most balanced in frequency response.

as has been stated, the circuit is most important and i would attempt to create as balanced a frequency response as possible.

Mrtennis: From your previous posts, I thought you preferred rolled-off highs -- caramel coloration? Do you now look for balanced frequency response? What kind of sound do you seek?