A little musing/brainfarting earlier in IRC left me with a lingering desire to build a tube preamp for the audio system in the truck...
Obviously it's not efficient. In fact the lack of efficiency is nearly being completely ignored. The only real efficiency consideration is using just a single 12AX7.
A zillion ohm plate resistance means the raw signal coming from the tube would be effectively useless to try and pump straight into the master pot... Will need some emitter follower trickery to get impedances back in check...
It's not entirely only about the majesty of tubes... there is actually a practical need. My primary audio source is one of my old phones, and between what seems to be anemic drive in the final in said phone, and the fact that the signal gets played with, isolated, split, and otherwise passively screwed with... By the time it gets to the Alpines, it's rather lacking.
What better way than for those times when an extra bump is needed, to use a good old fashioned valve?
Supplies are easy, methinks... For HV, the device that came to mind is an old cold cathode laptop backlight inverter... Should be plenty. For filament, a buck converter (pronounced "tweaked car cell phone charger") should be able to handle that with little issue.
Now, I know there's gonna be issues... Supply noise, impedance matching, and so on... but I don't think any of them are insurmountable... Heavy filtering and clever use of transistors following the plates, should come together without too much issue... The signal would legitimately be amplified by the tube, and add magic to the music for those "special occasions". The efficiency hit would be fairly well hidden by the gnarly suction occurring inside the power amps
I'm probably just nuts... but then again I'm building a solar oriented uhaul RV conversion... to live in full time... I can't have but so many marbles lined up... Shouldn't the tunes be able to at least reach full capacity?
Steve