Went back to the Vid and then went to the site.
Got this as some ideas...
The Evaluation board...
This "kit" if you watch the vid above - comes with a header to mount the tube...
Top side, where the tube will mount....take note that the board has a "blank header" to reduce microphonics ringing - as demonstrated in the vid...
Bottom side - showing solder traces...
Soldered in place...
Ok, the finished product...
It's a wild rebuild of an idea the Vacuum Tube Fluorescents can also be used as amplifiers.
The Phosphor as an emission electrode, wild idea but when you look at how these function on paper - they make sense.
Just remember not to overcook the filament that lights the phosphor.
Else can be made as small signal tube amplifiers.
Very Novel idea - especially for compact stereo equipment using a Vintage technology platform.
One small drawback, uses FET outputs - may be an issue on the breadboard for interfacing an analog device that may not like the shot noise and non-linear output of an FET directly.
Note the use of 330K resistor on the FET Strappnig Gate to Drain - for some linear operation. Frequency response notwithstanding - can produce some good fidelity. The 330K can be reduced will some improvement that comes with a loss of output - with improvement in bandwidth products.
Now remember - this is their plots, your mileage may differ...
Not sure of the actual signal level you can drive this - but looks like low-level dynamics would be just fine - the -2dB output at 12VDC is pretty good - but remember this output can be duplicated with a typical Electret - so again the Novelty and the glow - would be a nice addition to any system that uses low-level dynamic mics and cartridge outputs for entertainment.
Looks like the filaments are the biggest bottleneck, 0.7V 17uA - note one photo showing the red-glow - you have seen this on typical Calculator Vacuum Fluorescent Displays (VFD's) as normal, but remember that was for a display for considerable brightness, and digital drive output. So these do have a "headroom" dynamic issue of power input, so Filament aside- again low-level dynamics seem to be the best suited for this application.
Just not a lot of drive output - see the use of the FET output for line level. So its' possible; that with some rework even Germanium can be he next stage of the amplifier. Just watch the output of the ANODE - doesn't appear to summate the grid values - but can be driven with plate voltages quite high up to over 18 volts - can be a bit of a poke on the other end.
Noise? Note above in the graphics, a 10uF cap can be installed ABOVE BOARD - see photos above for location as C1 - for noise abatement - again, not a clear cut and dried use but can provide dampening of noise.
All the above - was from here...
https://korgnutube.com/en/guide/
Note the FET symbol - the GATE points to SOURCE lead - so bias feedback on Gate To Drain or Pins 1 to 2 on schematic reference.
Have fun!
:+> Andy <+:
