Multi-grid wrote:

On Oct 23, 6:01 am, maxhifi wrote:
Multi-grid wrote:
A properly designed Class A amp
never clips because the operating parameters were so chosen that it
runs out of signal from the intended source before it can clip (that
is one reason why the design instructions on my netsite feature the
*design center* process so heavily).

Stay on topic please.

While you're at it, please refrain from making personal attacks, it is
beneath you( I hope ).

Class A has nothing to do with its input signal. The finals clip
symetrically. Or perhaps unsymetrically if it is power limited A, so
to say overbiased given the load and B+. If you have plate dissipation
to spare, it is certainly possible. Matter of fact I am listening to
one such amp now...
cheers,
Douglas

I believe the point it changes from 'class A' to 'class AB' is commonly
accepted to be the point where the output stage begins to draw more
current from the power supply. By commonly accepted, I mean I've read a
ton of magazine reviews of tube amps where they use this logic, stated
almost exactly as Andre has used it.

In other words, the amp is biased a bit hotter than class B, and this
lowers low level distortion a bit at the expense of peak power output.

Stating that "the amplifier is Class A until XXX watts", really, is
telling you how hot the tubes are biased relative to the two extremes of
pure class A (full dissapation), and pure class (cut off).- Hide quoted text -

- Show quoted text -

Class A has nothing to do with dissipation either.

Class A has everything to do with dissipation!!!!

But lets begin with class B.
In class B, there is ZERO anode dissipation because the tubes ( or SS
devices )
are biased at cut off. The amplifier only has device dissipation when
signal flows.
But distortion is notoriously high, and to avoid the worst of it, class
AB is used
where the tubes/devices are biased with idle dissipation well below the
maximum allowable fpr the tube or device.
This allows a small amount of pure class A working power until cut off
begins to occur in tubes/devices
on each alternate wave peak.
Hence a pair of KT88 might be set up with Ea = 600V, and Ia at idle of
30mA, for a Pda at idle
of 18 watts. Maximum allowable for a single KT88 is 42 watts.
The AB power avaliable with 600V is around 100Watts class AB but the
pure class A might be less than 10 watts
for the load where 100Watts AB is possible, which will be a load a lot
less than the load required for
pure class A operation up to clipping.
Its possible to have two KT88 dissipating a total of 36 watts, Ea =
600V, and have a load which ensures all the power
is class A. It is a high ohm load, but achievable if you connect a 16
ohm speaker to an AB amp with an outlet
for 4 ohms; the reflected anode load of say 5k becomes 20k.
And the beam terode class A efficiency will be up to about 45% and so
you'll get a maximum
of 16.2 watts of pure class A power from a pair of KT88 with a total of
36 watts Pda.
If the Pda is raised to 72 watts for the pair by doubling the Ia, then
max class A
also doubles if efficiency is constant, so 36 watts is possible.

The load can be a lot lower as well.

I suggest you learn much more about basic output tube behaviour before
you shoot your mouth off
by saying that " Class A has nothing to do with dissipation either. "



Just because some
marketing group noticed that class A means something good, does not
make it right either. Just because it seems to make sense is no reason
to *******ize the definition. Find some other way to describe it.
cheers,
Douglas

You are looking like the one *******izing something imho.

Please clarify your reasons for whatever your stance really is.

Patrick Turner.