Composer, Programmer, Radio Amateur
Is it possible to build an audio amplifier on a single tube? My answer is, - yes, possible, and moreover, you can build a true high quality amplifier just on a single triode. All what you need is a tube with high transconductance which allows to have relatively high output power even on low input voltage given to the grid. Let's describe one scheme of such kind which I used for a long time as a base amplifier in my system.
Here is the complete scheme of the entire stereo amplifier:
As you can see, the scheme is very simple. With soviet 6J52P tubes on board it gives about 0.7W per channel. Output transformers were extracted from very old soviet tv-sets. They have transmittion ratio 35:1 and inductance of the primary coil about 10H. To get better bass response you should use transformers with higher inductance of coils. The nominal resistance of connected loudspeakers should be about 4 Ohms.
The power supply has minimalistic style too:
I used the 6Ц5С soviet vacuum rectifier there, but it can be easily replaced by everything else holding more than 100mA of current.
Building a model of the amplifier takes no more than 2 hours. If soviet tubes are missing in your cupboard, feel free to use other tubes. Maybe you will have less optput power, but anyway it should work. Don't forget to adjust voltage of battery and power supply dependant on type of the used vacuum tube!
The original scheme has very neutral distortion and can be used therefore for listening any kind of music. From Led Zeppelin to Karlheinz Stockhausen, Iannis Xenakis and Yossele Rosenblatt.