This circuit designed by Bruce and he has followed up his “OddWatt” project (EL84/6BQ5 Push-Pull) with the Oddwatt 225. The Oddwatt 225 is a scalable tube amplifier which will work with a number of octal tubes. In this build the driver stage is an SRPP with 6SL7 tubes and the output stage is a Class A UL SIPP with KT77 tubes. LM317 Regulators are used for the cathode CCS. source

This is a simple do-it-yourself (DIY) headphone amplifier project that is fashioned primarily after the Class A MOSFET Headphone Driver project by Greg Szekeres and to some extent Mark’s DIY Class A 2SK1058 MOSFET Amplifier Project. The amplifier concept is simple and follows a typical single-ended class A circuit utilizing an active constant current source (CCS) in place of a passive resistor. A CCS doubles the efficiency of the circuit over that where a passive load resistor is used, bringing it to a maximum of 25%. source

When experimenting with tube amplifiers, you might be confused about the different modes of operation, like triode or pentode mode. Here is the developed circuits which you can build small Amplifiers based on 6P14/6BQ5/EL84 easily, and the output Power of 2.6 Watts is more than enough for home use. Also,the PCB included.With this PCB you can try out the different Modes by means of Jumper Wires.source

This is a reliably high sound quality audio power amplifier project based on the National Semiconductor’s LM1875 IC. The circuit that we give is a similar form of the application circuit in the datasheet that NS provides. It is really easy to build and low cost. The voltage gain of the each monolithic channel is 27dB.source

Ultra-Linear operation provides a compromise between the high efficiency of tetrodes and the low distortion and uncritical load impedance of triodes.There is an undoubted advantage in modulator service because the matching of the modulator to the RF stage is not so critical and the screen (DC) supply is obtained “automatically” from the transformer.source