The subminiature tubes like the 6111 have an indirectly heated cathode, which can be just as hungry as the 7 and 9 pin miniature equivalent (12AU7 in the case of the 6111).
I did make a tiny guitar amp years ago with a 6112 (like a 12AT7) driving a 6AK6. Sort of a low voltage (90 Volt B+) Fender Champ.
There were several types of subminiature and smaller directly heated tubes designed for hearing aids in the 1940's / 1950's in the USA. Since the market was small, they are somewhat scarce. So are some of the data sheets. There are also military tubes for things like missile guidance, but tubes and date are even scarcer.
Some of these ran on 1.5 volt filaments in the 10 to 50 mA range. Most have an odd 4, 5 or 6 wires in a row base intended for directly soldering into the circuit. There are sockets which are rare, but machined pin IC sockets work well. The 6418 is a "power pentode" capable of a metal shredding 2 MILLIWATTS of power from 22 volts of B+ with a 1.25 volt 10 mA filament. Use it to drive a mosfet follower since, like the VFD's it can't drive anything but a '40's vintage crystal (piezo) earphone on its own.
Most of the battery tubes that were intended for portable radios are somewhat microphonic since that thin heater wire can vibrate. The 1.5 volt heater power can be generated from the main battery or wall wart using a little switchmode voltage regulator. It isn't usually too hard to find little 1 to 5 watt DC to DC converters on the surplus market for a few $$$. Look for the ones made to generate 3.3, 3.6 or 5 volts from 24 or 48 volts DC. Wire the filaments of the tubes in series, or use a tube with a 2.8 volt heater and a resistor.
Somebody in China is still cranking them out. Our 2 year old GE microwave has a VFD in it.
I did make a tiny guitar amp years ago with a 6112 (like a 12AT7) driving a 6AK6. Sort of a low voltage (90 Volt B+) Fender Champ.
There were several types of subminiature and smaller directly heated tubes designed for hearing aids in the 1940's / 1950's in the USA. Since the market was small, they are somewhat scarce. So are some of the data sheets. There are also military tubes for things like missile guidance, but tubes and date are even scarcer.
Some of these ran on 1.5 volt filaments in the 10 to 50 mA range. Most have an odd 4, 5 or 6 wires in a row base intended for directly soldering into the circuit. There are sockets which are rare, but machined pin IC sockets work well. The 6418 is a "power pentode" capable of a metal shredding 2 MILLIWATTS of power from 22 volts of B+ with a 1.25 volt 10 mA filament. Use it to drive a mosfet follower since, like the VFD's it can't drive anything but a '40's vintage crystal (piezo) earphone on its own.
Most of the battery tubes that were intended for portable radios are somewhat microphonic since that thin heater wire can vibrate. The 1.5 volt heater power can be generated from the main battery or wall wart using a little switchmode voltage regulator. It isn't usually too hard to find little 1 to 5 watt DC to DC converters on the surplus market for a few $$$. Look for the ones made to generate 3.3, 3.6 or 5 volts from 24 or 48 volts DC. Wire the filaments of the tubes in series, or use a tube with a 2.8 volt heater and a resistor.
Somebody in China is still cranking them out. Our 2 year old GE microwave has a VFD in it.