Phase Inverter Duty - Sound/Function or Both?

[jgab]

Hi,
I am aware that the phase inverter tube is functional for p/p output tubes, but does it color or shape sound on itself like a V1 tube?

I guess what I am asking is: Will the tube itself have a bearing on sound, or is it just altering the characteristics/performance of the output tubes?

Thanks,
J

[krx]

Yes, it affects the characteristics of the sound. Anything that passes audio signal can have a major impact. The phase inverter in the 18W splits the signal, provides some gain, and drives the output tubes. Small changes to the circuit will mostly affect the overdrive character. As far as swapping in different 12AX7 tubes, you'll definitely hear some difference but it won't be as large as from swapping the first tube.

There's actually a lot of different ways you can build a phase inverter. The 18W and most other modern amps use the AC-coupled long-tailed pair. But you can also have a DC-coupled LTP (Hiwatt), a cathodyne (aka concertina) as used in the 5E3 and lots of other amps, a paraphase (really old Tweeds, Supros, etc.), and some more exotic types that usually only pop up in hi-fi amps.