The opinion that a tube amplifier is necessarily expensive is completely untrue. Homemade amplifiers of this type are affordable for everyone. It is enough to have the skills of assembling these devices.
Take a 50W power transformer. It must have two secondary windings, one of which develops an alternating voltage of 150 V, and the other 6, 3. Its primary winding must be rated for a voltage of 220 to 240 V.
Do not pay attention to the fact that most industrial and homemade tube amplifiers have at least two stages. Modern sound cards develop a signal at the output with an amplitude that is quite sufficient to feed 6P14P lamps directly to the grid.
Connect the input of a rectifier bridge designed for a voltage of at least 500 V and a current of at least 500 mA to the 150-volt winding of the transformer. A section of the board with such a bridge, assembled from individual diodes, can be cut, in particular, from the board from a failed energy-saving lamp. When disassembling it, be careful not to touch the filter capacitor leads. To the bridge output, observing the polarity, connect an electrolytic capacitor with a capacity of about 30 μF, designed for a voltage of at least 500 V.
Connect the negative terminal of the capacitor to the common wire of the amplifier, and the positive terminal to one of the terminals of the primary winding of the output transformer. The latter is much smaller in size than the power one, and should be designed specifically for tube equipment. Connect the other terminal of the same winding of this transformer to the seventh terminal of the 6P14P lamp. Also connect the positive terminal of the same capacitor to the ninth terminal of the same lamp through a resistor with a resistance of about 10 kOhm, designed for a power of at least 1 W.
Connect the third terminal of the lamp to the common wire through a 200 ohm resistor. In parallel with this resistor, connect an electrolytic capacitor with a capacity of several microfarads, designed for a voltage of at least 16 V (minus to the common wire).
Connect pin 2 of the lamp to the common wire through a resistor of about 500 kOhm.
Connect a speaker to the secondary winding of the output transformer. Also connect one of its conclusions to the common wire.
Connect the filament winding of the power transformer to terminals 4 and 5 of the lamp. Additionally connect one of its conclusions to the common wire.
Apply a signal to the connection point of the second terminal of the lamp and the resistor through a capacitor with a capacity of about 0.1 μF relative to the common wire.
Connect the primary winding of the power transformer to the mains through a fuse rated for a current of 0.25 A. Adjust the volume with the computer mixer. After making sure that the amplifier is in good working order, de-energize it, and then place it in a housing that is resistant to heat, dielectric and excludes touching the live parts of the device.
If you want to make a stereo amplifier, build a second output stage of the same type.