can i use 6550's?

[Jana]

"And people seem to be forgetting that tubes don't "pull current", they just regulate it. Think about your load line, they are the exact same no matter the tube. The only difference is how close to 0V it can go before the grid becomes positive, that's when you're pulling max current. This is the big reason why Triode strapping reduces power.

So putting 6550s in there won't make a drastic difference in current demand. Don't fret it that much. "

And this is based on what? Do you have a copy of this load line that is the same for all tubes? Does it work with all voltages and P to P impedances? I sure would like to see it.

Take a pair of EL34's. B+ 470. 70% bias gives 75 ma. current draw at idle.

Take a pair of 6550's. B+ 470. 70% bias gives 125 ma. current draw at idle. Add in about 15 to 20 ma. for the screens and the rest of the amp and that 150 ma. transformer is at the limit and the amp isn't doing anything yet except sitting there and idling.

We haven't even touched on Imax yet.

We ARE talking about amps, not toasters.

[iknowjohnny]

Wait jana....thats a great idea....lets DO talk about toasters ! Now, what is your fav tube in a sunbeam 4 slotter?

[Jana]

You have a 4 slot toaster? I'm jealous, I only have a two slotter.

EL34's work good for toasters--the softer vacuum makes the tubes heat up better. But, for things like Toaster Strudel that burns easily, then 6L6's with the hard vacuum is easier to control (less heat).

[iknowjohnny]

Well, i don't eat much strudel so i think i'll stick with el34's. They seem to work good with eggo waffles.

[Badside]

And this is based on what? Do you have a copy of this load line that is the same for all tubes? Does it work with all voltages and P to P impedances? I sure would like to see it.

Take a pair of EL34's. B+ 470. 70% bias gives 75 ma. current draw at idle.

Take a pair of 6550's. B+ 470. 70% bias gives 125 ma. current draw at idle. Add in about 15 to 20 ma. for the screens and the rest of the amp and that 150 ma. transformer is at the limit and the amp isn't doing anything yet except sitting there and idling.

The load line itself is a function of impedance and voltage, no matter what tube you're sing (this will influence the characteristic curves, which in the end decides your maximum current/voltage swing).

But of course, if you increase the idle current by 50mA, obviously your PT will be working harder. It's not written in stone that you have to bias to 70% at all cost.

[Jana]

I never said the 70% was cast in stone--I only used that as an example. I doubt, however, that biasing the 6550's to 42% would be desirable for an audio amp. This is what would be needed to have a similar current draw at idle as the EL34's.