1) The real advantage that contemporary amplification has (over *most* tube designs) is that the output devices don't require a transformer and the power supplies are at lower voltages.
2) Solid state devices based on the transistor are smaller, less expensive and don't use much power (compared to tubes).
3) Beware any tube device where the tubes are used as buffer stages, and don't actively amplify the signal.
1) Your reference to OTL amplifiers? Those have been, historically, a semi-commercial 'success' (LOL) for driving high voltage electrostatic panels and high impedance conventional loudspeakers. Acoustat Model X was an example. Also, the Beveridge Model 2.
Stand alone OTL amplifiers, the most famous being Julius Futterman's design, have been mildly 'success' in the niche market. Perhaps more known about than ever seen. Julius hand made them in his Manhattan apartment, and a handful were factory built under license, using the Harvard Electronics name. Later, after Julius' death, a modified design was sold by Harvey Rosenberg under the New York Audio Lab moniker. Futterman amps featured tubes found in television sets, and were said to work well with loudspeakers that didn't dip much below 8 ohms. Anything less and they'd become unstable, and blow up. At least that's the story Harvey told. from his warranty bench.
2) None of the above were inexpensive, for sure. But always smaller and less expensive? While usually so, the Class A phenomenon one sometimes runs across (thanks for that, Mark) are certainly as expensive, large, hot, and as hungry for electricity as tube amplifiers.
3) Some phono amplifiers (such as the Bellari) use a tube for 'buffering' or modding (muddying?) the signal. In the Bellari, primary amplification is an opamp. On the other hand, I have a hand built phono preamp that uses a JFET for the first stage (low noise) and dual 12AY7 tubes, then going to a 12AX7 line stage. Just know what you are spending you money on. Designs like the Bellari (raved about by Mr. Analog, Michael Fremer, by the way) seem to me to be fraudulent in their advertising because they don't state up front what is going on within the circuit.
Power amplification has often used 'hybrid' tube/SS combos. George Kaye's NYAL Moscode, and perhaps Bascom King's amplifier being the best known examples. Michael Elliot's Counterpoint designs also come to mind. I'm sure there's a lot more.
Moving to the associated audio world, RF applications use tubes, last I looked. Also, of course, in musical instrument amplifiers, where tube distortion is favored. Some of the latest SS 'digital modeling' amps certainly come close to mimicking the 'overdriven' tube sound, but at a price.
I think the benefit of tubes for a hobbyist is that there are a lot of designs out there the average cat with a soldering iron can easily build, many based upon 'old' Dave Hafler/Ed Laurent Dyna designs. These are generally simpler assemble and test than high powered SS designs. Certainly at night they tend to look cooler in your system (although running hotter
).
