Tube preamp topologies and music

I do not recommend single-end (one output tube per channel) amps because they typically have low power and high distortion/noise with high output impedances. The last means that the amp will track the impedance curve of the speaker, meaning it will yield a non-flat response, acting like a tone control. Something to be avoided!

A nice thing about the ST70 is the availability of various tube options for the input stage using different dual triodes to replace the stock pentode/triode. Mine uses three dual triode 6922's along with higher-quality capacitors. Plus you can try different brands of EL34's for different sonic "flavors".

An 8 watt single-end 300B amp would be strained to drive a Klipschorn to adequate levels for hard rock/metal because past 2 watts distortion skyrockets to 5 - 10%. Add the inability to provide enough current for the typical 10 - 12 inch woofer and you have an amp with very limited usability.

 All single-end tube amps are best used when power levels don’t exceed 25% of maximum wattage. Otherwise distortion climbs rapidly. Plus signal-to-noise (SNR) ratios are poor due to lack of common-mode noise rejection available in push-pull designs.

In my tube amp collection I have several single-end amps: a 45, a 2A3, a 6BG6 and a 6L6GC. The last is the Golden Tube SE40, which uses three 6L6GC beam tetrodes per channel to yield 20 watts. Much more usable than the 45 (1.75 watts), 2A3 (3.5 watts) and the 6BG6 tetrode (7 watts).