Early Magnatones used basic radio amplifier circuits and common radio tubes, like the 6V6 and 6SJ7. Like a lot of post-war amplifier companies, Magna used war surplus tubes, and would buy large lots of tubes. If a circuit used a 6N7, and the re-stocked 6SN7 or 6SC7's, they tweak the circuit for those tubes. I've even seen Magna's with 7C5 Loctal tubes (a 6V6 with a different base).
When the 200 series came around, louder amps were required, with slightly more sophisticated circuits. The 6CZ5 and 6973 were used. In 1963, engineers redesigned circuits to use the GE 7189A and 6GW8 tubes. To maximize buying power, nearly all Magnatones were designed ot use one or the other.
Preamp tubes configured for gain general draw a low current and don't wear out. The sixties Magnatones were built with high quality Mullard preamp tubes. I don't think there is a new production 12AX7 that can match the audio fidelity of those original tubes, but even low current 7025s can develop problems of ghost noises and thuds. Lots of Magnatone preamp tube types are still in production so let you ears be the judge.
Power tubes are a different story. They do wear out. With Magnatones, however they don't wear out like they do in Fenders. Magnatone engineers were careful to obey datasheet maximum limits and set bias of power tubes conservatively.