Here is a project for music lovers. Although electronic tube or valve era is long passed, these devices are still used in high quality audio applications. It is true that you won’t wont find them in every home because their regarded as obsolete or too exotic. Guitar players are the ones who know and appreciate their sound as many famous guitarists use tube amps to drive their instruments. Stereo amplifiers built with tubes for hi-fi applications are still being made today and their cost can be pretty high as these amps are though to deliver high quality sound.
The reason tubes have a specific sound has to do in my opinion with the fact that tube distortion is mainly second order which is more music-friendly than the 3rd order distortion that solid state devices have. Some say this is because in tubes you control the flow of electrons and only electrons carry your information unlike transistors.
Depending on their output stage configuration tube amps can be single ended ( using only one tube working in class A) or push-pull ( like with transistor using two tubes working either class A or class AB). Because of the high output impedance of tubes they need an impedance transformer to drive the speakers. This is also the reason of their low damping factor which in combination with their usually low power output makes these amps suitable for certain types of speakers. From my experience you will need speakers with big woofers and very efficient (high SPL per watt). Also i have found that single ended amplifiers ( in class A of course) with high anode voltages applied are best when tube-like sound is desired.
Returning to the project at hand, it is a push-pull design using 6v6 pentodes connected as triodes. If you get an ultralinear output transformer you can use the 6v6 as pentodes. The input stage using a 5965 double triode is as simple as it gets. It amplifies the signal in order to attack the final stage and provides phase inversion necessary for push-pull. The power supply uses semiconductor rectification which i find a bad thing for a tube project. There are tube diodes available for this task.
As with most audio high fidelity projects the quality of the sound is in strong relation with the quality of the build. If you do this project just for fun then you will be happy with it just working, if you build it to experience tube sound you should take greater care at layout and components you use. Using multiple transformers is a bad thing as they introduce noise. Using one transformer with many output voltages is alot better. And screening of the transformers is a must. In the project link you will find many advices on how to build it even though the builder didn’t follow all of them.
Another thing, and a reason that keeps many diy-ers away from tubes, is that you will be dealing with high voltages. Be very careful with that. And to close this presentation with another advice don’t use it to amplify your iPod.