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.

Hmmm, pardon me but IMHO,NOT ALWAYS THE CASE! It depends on the design of the circuit. In preamps, maybe but in amps not always.

For example, you have a 45 SET amp whose output tube Power Dissipation (Pd) is operating at 10 Watts maximum rating (as specified by RCA receiving tube manual) using a 5Y3's. What do you think would happen if you use a 5V4?

5V4, tube voltage drop is 25 volts at 175 ma. max I=175 ma.
5Y3, tube voltage drop is 60 volts at 175 ma. max I=125 ma.

Good bye 45 tube!

One way to identify the tube is to post a pic showing the plate structure of the tube. Most of the time, the 5V4's in ST bottles are flat plates. Also, you can use a magnifying glass to look for any trace of the faded markings on the tube, usually for RCA, the mark is directly in line with the guide pin as you go up on the glass.

>>No, but 5V4s and 5Y3s are basically interchangable<<

No, they are not.

For example, 5Y3 is a popular rectifier for 2A3 amps and 5V4 for 45 amps.

Now, using your assertion, stick that 5Y3 into the 45 amp and watch the snap, crackle, pop action of your triodes.

Very bad information.

"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.

Audiofeil,

I know you know much more about tubes than I do, but I'd always read (or at least thought I had) that you could use a 5Y3 with either a 2a3 or 45, and that it is the 5v4 that should not be used with a 45 triode.

Am I mistaken?

Try putting the tube in the freezer for a while, sometimes the markings that have been wiped off will show up in the frost.

Sorry, Darosenb my post is in error. The idea was correct but the typing was not.

An amplifier manufacturer I represent vigorously cautions against using the 5V4 with a 45 as you point out.

The 5Y3 is appropriate for the 45 Triode and could work with the 2A3 in many circumstances.

My bad.

Don't try this at home.

???? 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.

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.

I suggest you read some more! At 11 watts Pd of a 45 tube specified at 10 watts, draw your own conclusion. Different transconductance or not, we are talking about increase in B+ resulting to Increase in plate voltage are we not?

Audiofeil does not need to explain it to you. It has something to do with Operating Points where the tubes are bias. But your statement says "5Y3 and 5V4 are always interchangeable", what we are trying to say is IT DEPENDS! You have to know where the output tube is operating before saying a blanket statement like that.

BTW, why are you concern about current levels when voltage already increases and tells you that the power did the same?

Yes, a 5Y3 can be substituted with a 5U4 because in using the latter, the filament supply was already establish that it can take 3 Amps draw. A 5Y3 only takes 2 amps. But, this is a different scenario over all and not analogous to substituting 5V4 to 5Y3. VERY BAD INFORMATION!

Ahh, I am out of here! You guys decide what is right and wrong. Consider my post as such, with no real info. I forgot that this is Audiogon after all. Sometimes I wonder why do I have to participate in threads like this. If someone can show me how to delete my previous post, please let me know.