Difference bewteen ultralinear & triode mode?

[kevinkuang]

Hi,

besides the low distortion/low power vs high distortion/high power, and of course the connect mode is different, what's the sonic difference bewteen these two modes? I tried my KT88, it seems the triode mode is more smooth, how about your amp? Which one is "considered" better?

Thanks for sharing!

[leadbelly]

I know one of them has better depth, imaging, and transparency, but I just can't remember which!

[Positron]

Been a long time since I have run that operation.

UL has higher output Z and lower damping factor vs triode operation. Bass is certainly "more" but "looser".

[kevinkuang]

simply ask, which one is supposed to be better?

[SY]

Better for what?

Look, if there was one amplifier topology that was "better" in some Platonic sense, everyone would be using it. The proliferation of a wide range of topologies ought to answer your question.

[kevinkuang]

I dno't want to play word game here.

Does anyone know what's the idea behind the triode mode, technically? and according to the sonic difference, is this idea successful?

[Sch3mat1c]

Triode mode, electrically and physically, turns a tetrode or pentode into a triode by connecting the screen to the plate. You regain the plate resistance phenomenon (unique to triodes: pentodes, FETs and BJTs have no similar internal feedback mechanism and as a result have a constant-current output characteristic) by putting the plate's changing electric field immediately outside the grid, as happens by design in any normal triode.

Unfortunately this dramatically reduces perveance, reducing output power. A single 6L6 can produce 8W in pentode, dropping to a measly 1.6W at the same voltage, just for tieing screen to plate!

Distortion goes down a bit, compare 10% THD to only 5%; however, the same drop in gain can be had with local or global NFB, which is linear, and get 1 or 2%, at five times the power output to boot! (The screen grid is a nonlinear input, at least when moving in step with the output.)

Tim

[kevinkuang]

then is it saying that triode is supposed to be better than ultralinear? I know they are different, and might be not comparable, but what's sonic difference?

[planet10]

As a generally held belief triode mode is better sounding... recent amps such as the RH84, Gary Pimm's 6AU6/47 PP, & Pete Millet's amp in the latest aXp are challenging that belief.

On the weekend, we converted a Mulligan (SE EL84 triode strapped) into an approximation of an RH84 (using parts on hand). Good enuff that it is going to be updated with proper parts & if long term auditioning verifies initial impresssions the more developed SE EL84 parafeed monoblocs will also be RHed... RH runs in pentode mode... the same feedback trick probably works with ultralinear (ie Peter Wendt)

dave

[audiousername]

It's interesting how things go out of fashion, then back in again.

Using the feedback method which Dave was suggesting may impose a more severe load (lower impedance) to the driver - so was often considered a poorer choice than using global feedback from the secondary, as is commonplace now. It is most certainly not new - I just was browsing through the "Has anyone built this amp?" thread, and noticed something (this is apparently a fairly typical circuit for a '40s valve radio)
http://www.wkinsler.com/radios/5tubeamp.html

Notice R8?

Anyway, back to the original question - all of fixed screen (pentode), ultralinear, and triode mode have good and bad charateristics. There is no "best" choice.