name that tube

No, but 5V4s and 5Y3s are basically interchangable . . . the 5V4 IIRC has a bit higher current capability and a little less forward voltage drop, but the differences aren't huge.

"Goodbye 45 tube"??? Give me a break.

A 10-watt tube in SE class A has . . . what, 250-300v on the plate at 35-30mA? So changing the B+ by 35v will change the plate dissapation on the output tube by about 1-1/2 watts . . . differences in transconductance across various 45s will cause at least this much varation.

Not to mention a variation in line voltage by 10% . . . again, the differences AREN'T huge. But I guess if you own/build an amplifier that runs all the components really close to the bleeding edge, then maybe EVERY tube should be hand-picked and measured first.

???? What? Are you guys kidding me???????

Audiofeil, why don't you explain to me the electrical mechanism by which a 5Y3 will make a 45 "snap, crackle, [&] pop". Does the 45 look around, and upon seeing another directly-heated cathode . . . commit some sort of spectacular suicide out of jealousy? If anything, the 5Y3 is the one to exhibit higher stresses, and if you were pulling something like 100mA, then a 5Y3 wouldn't last very long, but a 5V4 wouldn't last a whole lot longer.

So again, what current levels are we talking about for a 10W SET amp? A 5Y3 can withstand years of hard use in a Fender Princeton, Harvard, or Vibrolux, at like 50-60mA, 400-ish volts. 5V4 is a VERY common sub for these applications that gives a tiny little bit more volume and crunch. I've even seen people getting cheap and using a 5Y3 instead of a 5U4 in Supers and such . . . not really a very good sub, but it WILL play for years this way, and unless somebody over-fuses the amplifier . . . no damage will be done, even if it fails.