How does a VAC Renaissance 70/70 get 65W from 4 300Bs?

[Saurav]

http://www.vac-amps.com/page0011.html

This has me pretty confused. It says it's PP, which means 2 tubes paralleled for each half, right? That should be 8*4 = 32W, or at most 40W. Is there something I'm missing here, or do they just push the tubes that hard, and get 16W out of each 300B? How long would the tubes last at that operating point?

Does anyone have any experience with these amps?

[Saurav]

Never mind, got the answer from Kevin Hayes @ VAC. I didn't know WE has specified operating points for a 300B that go up to 17W output per tube.

[Brett]

Originally posted by Saurav
Never mind, got the answer from Kevin Hayes @ VAC. I didn't know WE has specified operating points for a 300B that go up to 17W output per tube.

In AB1

[grataku]

AB1? Does it mean there is an AB2?
Can someone point to a link that explains the various classes when talking tubes?
There seem to be lot more sub categories than there are for SS amps.

[SY]

With tubes, the classes are pretty easy. You know what class A is- the idle current is the same as the max current. (180 degree operating angle)

Class B has an operating angle near zero degrees; in other words, its idle current is negligable compared to max current.

Class AB is in the middle. Its idle current is below the max current, but is still significant.

AB is subdivided into AB1 and AB2: in AB1, no grid current is drawn. In AB2, the grid is allowed to draw current. This requires a heftier driver stage.

By and large, you don't see AB2 that often.

There's also class C, but that's never used for linear amplification in audio. It's very efficient, very useful if you can bandwidth limit it severely, and is commonly found in RF transmitter circuits.

[Saurav]

In AB1

Soooo....

Renaissance 70/70 abridged specifications
Power: 65 watts / channel pure Class A dual-mono

It can't be class A for the full 65W? Or can they design it for that, and then it just eats through tubes somewhat more quickly than more conservative operating points?

[dhaen]

I've never see an engineering definition of:

pure Class A

Does it mean anything? Somehow I doubt it

Cheers,

[Saurav]

You know what class A is- the idle current is the same as the max current.

This is probably a really dumb question, but I never understood that. I've understood class A as a tube that's conducting for the entire sine wave cycle. For PP, I can see how this means idle current = max current, because as one half conducts more the other half conducts less. But for an SE stage, is the idle current still the same as the max current? How does that work? The tube moves up and down the load line, right, so the current should be changing, shouldn't it? So idle current should be 50% of peak current.

Hm. If that's true, then a PP stage not only cancels out even order harmonics, a class A PP stage also presents an easier load to the power supply. It's probably really funny that I just realized that.

[EC8010]

Hello Saurav, you are correct on all counts.

[fdegrove]

Hi,

Class A is the same for a PP amp or a SE amp.

Even Class A is subdivided into Class A1 ans A2.

An overview:

Cheers,