pentode mode / triode mode? please explain

[Mark]

I want to buy some Yellow Jackets or Ruby Tonebones.
I'm told the YJ's operate in pentode mode and the Tonebones operate in triode mode.

Do I need to know what this means before I make a purchase?

[John Phillips]

'Triode mode' is a way of connecting the grids in a pentode (the normal type of power tube, including EL84s) so that it behaves 'like' a triode - a simpler, less efficient type of tube. This produces less power - 40 to 50% less, usually. But it isn't the same as using an actual triode, and running a pentode like that significantly shortens its life, largely because the screen grid is being asked to handle currents it was not designed for.

[scottl]

John,

If an amp, like my Rivera, has a modern/vintage switch (pentode/triode), will that also shorten tube life??

Many amps have such a switch. It is available on the Fuchs as well.

Scott

[John Phillips]

Originally posted by scottl
If an amp, like my Rivera, has a modern/vintage switch (pentode/triode), will that also shorten tube life??
Yes.

I think (but I'm not certain) that the effect is less serious with a 'beam tetrode' - eg 6L6, 6V6, KT66, etc - than a true pentode, eg EL34 or EL84.