Switching to solid state amp?

A sonically excellent power amplifier should exhibit high input impedance, very low output impedance, flat frequency response, and ultra low distortion. And it should do all of this without contributing any extraneous hum or noise. In addition, it should also be capable of producing unclipped power output that's some 2 or 3 dB more than your loudspeakers can tolerate.

It first became practical to build a power amplifier that meets all of these requirements back in 1976, when PNP silicon power transistors finally became affordable, thereby permitting fully complementary differential solid state circuit design at reasonable cost. And that's when I personally left vacuum tubes behind, in the past, where they belong.

While it's theoretically possible to construct a tube-type power amplifier that will approach the described design criteria, that product will exhibit persistent vacuum tube degradation that begins at initial turn-on and ultimately ends in cathode depletion failure—barring other modes of premature demise (e.g. open filament, vacuum leaks, gassing, microphonics, atypical distortion, hum/noise). So vacuum tubes are not a wise choice when stable, long term circuit performance is a serious design goal.

There's nothing "modern" about vacuum tubes! Indeed, vacuum tube commerce has collapsed in the 40+ year lapse since I last used a tube-type audio amplifier. All of the principal domestic, British, Dutch, and German producers are now either defunct (like Tung-Sol Electric, my employer from ’57 - ’60), or they’ve long since ceased making tubes. The entire world market for (receiving-type) tubes is now confined to a small coterie of audio and guitar buffs, and served only by obscure Russian and Chinese suppliers with no previous market recognition. (There are other minor sources in former Soviet bloc countries.) The quality and reliability of the tubes made by those arcane foreign suppliers is a subject worthy of concern. And those sources will persist only as long as there’s viable demand, so the outlook for assured access to replacement stock seems dicey. Further, this situation prevails at a time when every instrumented means of evaluating audio quality validates the measurable superiority of modern solid state design, so it's hard to envision an audio future that will extend vacuum tube usage.