Patrick Turner wrote:
WakyAmps wrote:
Patrick Turner wrote in
:
Miles O'Neal wrote:
Patrick Turner responded to WakyAmps, who said:
Actually, it was Miles who said... but I've a few questions of
my own.
[humongous snip]
Not sure we're all speaking the same language here ('least I'm
sure as hell not...)
In my dictionary[1], a push-pull amp biased class B has one
output tube in cutoff when the other is conducting. Class A has
both tubes conducting for the entire waveform. Class AB1 has
each tube conducting for somewhat more than half of each cycle,
though the outputs still alternate between cutoff[2].
I think we'll all agree that an AC-30 runs the bejeezus out of
its outputs. However, please explain to me, for a P-P AB1
biased amp, the difference between the "Class A watts" and the
"Class B watts". I don't think I've ever seen those terms used
in that context before.
Most guitar amps are class AB1 amps.
This means that for say the first 5 watts, both output tubes
operate with low distortion content in their currents,
and are like two single ended tubes but working together to change the
opt primary
voltage in a balanced manner.
Beyond the 5 watt power level, one of the tubes recieves a large enough
negative going grid voltage to cut the current flow right off.
The other tube grid is getting a positive going voltage to turn on the
tube
current much more, and so power is produced by one tube only
during the crests and troughs of the sine wave. Only the zero crossing
part of the sine wave power cycle is where both tubes mutually
contribute power.
So over 5 watts in the above typical amp, the power can be said to be
classB.
But viewed as a whole, during a maximum level sine wave,
the operation is class AB.
AB1 indicates tubes are not driven to draw grid current, AB2 means
the amp is driven hard to make the grids draw grid current.
Once upon a time, nearly all makers used a much lower screen voltage
than today, where the trend is to have both anode and screen supplies
quite high, say both at 450v.
Originally, 6550 and 6L6 and 807 were configured with screens
set at 300v max, and then anode voltages could be much higher.
Even 807 were run with 600v at the anode, and 300v for screens,
and 80 watts class AB2 were available.
The lower the screen voltage, the lower the grid1 bias voltage,
and the lower the AB1 power output ability into a low value RL.
So to get more anode swing, the grid1 is damn well forced to swing
more, and above 0V ie, positively, when it conducts current,
so a cathode follower drive stage is required.
The result is that the screen currents overall tend to stay low, and the
screen dissipation
tends to stay well within the operational ratings, and the tube lives to
a ripe old age,
and it don't die screaming.
Are you saying that an AB1 amp where the outputs conduct for,
say, 80% of the signal has more "class A watts" than an amp
where the outputs conduct for 70% of the signal? The latter, of
course, having more "class B watts"?
Indeed.
Most guitar amps have maybe 5 watts of what is class A power,
and the remaining 55 watts are class B.
That's a total of 60 watts of class AB.
Oops, oops,.... stop right there.
You have forgotten to mention the Fluff Factor, as it relates to all this, amplifier to
amplifier.
You see many do not know, or if they know, believe in the existence of the Fluff Factor.
Or, many times, is not even noticed, like the slight of hand of the magician.
Yeah, each amplifier is actually pull a slight of had act one most experts, and they are
not even aware of it at all.
THAT, is because they are SO caught up in the moment of analysis, speculation, and
theory,... that they totally miss the Fluff Factor.
So what you are going to ask is, what is Fluff, and the Fluff Factor...
OK, coming up.
In the above explanation, on assumes a stable voltage to be in place on two elements of
the tube.
Of which, it is not, and varies amplifier to amplifier.
Thus creating that ever popular problem of, the numbers don't line up exactly right.
Like, for some reason there is the appearance, there are a few missing and unaccounted
free electrons who got lost somewhere.
Where did they go!!!!!!
Well, it have been found that Fluff Factor is directly proportional to the number of
missing free electrons.
Hey, what the hell is a few missing electrons anyway.
But, when the number of missing *In Action* free electrons starts to grow in number, and
no longer can go un-noticed, the Fluff Factor goes through the roof!!!!!!!!!!!!
For Example, take the amplifier supposed for the case in point. Which was used in the
explanation above.
We all sat here nodding our heads in front of the monitors. Right!!!!!
You were so focused on the hands of the magician and things looked like,... Hey, we're in
the REAL world, and everything is cool.
But, if you re-wind the tape, and replay it through another amplifier, you are going to
get a DIFFERENCE.
So, in order to establish this existence of Fluff, and the Fluff Factor, we have to set
some rules, or if you will, a standard for both cases.
The original explanation, and the one to come. Thus, producing the presence of Fluff, and
the resultant, Fluff Factor.
First, the input to output CHARACTERISTICS of the amplifier, which is the basis of the
original explanation, for the support of this explanation of classes of operation of an
output stage, MUST be documented precisely, in EVERY way possible.
Remember, everything about this amplifier is assumed to be IDEAL!!!!!!!!!
But, it isn't.
It isn't IDEAL!!!!!!
So, for the moment, let's make some changes to that original amplifier, so there will NOT
be any assumptions about anything.
The First Thing, we are going to do, is make this the ideal amplifier, by disconnecting
ALL the internal voltage sources. A complete, power supply, disconnect, with all its
branches.
Then, in the place of these disconnects, is attached laboratory grade power supplies,
throughout the amplifier.
One for just the filaments of those output tubes.
One for the bias supply to the control grids of those output tubes.
One for the screen grids of those output tubes.
One for the the anodes of those output tubes.
One for each stage in front of the output stage.
Each is a regulated variable voltage source, with unlimited current availability.
In short, ZERO sag EVERYWHERE.
NOW, let's match the exact voltages found in the original amplifier, and repeat this
again, and compare the differences.
Well, doesn't this change things a bit!!!!!!!!!!!!
I guess you can now SEE a piece of the Fluff now.
You you are SURE as Hell, going to be USING IT, as soon as you take a breath to comment on
this so far.
But there is more yet, to be seen, than the obvious with respect to the anodes of the
output tubes now.
And that, is the the simultaneous impact, that the CHANGE, from sagging power supply has
on both the AC and DC characteristics, changing AC to DC ratio of the output stage,...
Plus, the change of input drive to the output stage from such.
Now, think of ALL those external power supplies, now supplying unlimited energy to the
amplifier system.
Now, compare those input data sheets of both examples, and tell me now, how those amps
line up again.
Did those 6550's meet max specs.
For that matter, how do those output tubes match the curves for the GE-6550A now.
Hey, those curves are from a naked tube with lab supplies on them.
Zero variables present.
Which is not the case with all the case points offered in support of polished turds.
The friend to a Polished Turd is, a sagging power supply!!!!!!!!!!!!!!
What, what did you say!!!!!!!!!!!!!!!!
Oh,... that.
Sorry,.....
Fluff, is the of verbal tap dancing used by the experts to glorify the Polished Turd from
a technical point of view!!!!!!!!!!!!!!!
Huh, what,.... Oh!, the Fluff Factor!!!!!!!
THAT, is the *amount* of *fancy foot* work required to explain those NEW FOUND, missing
Free Electrons, from before, that now appear to now be flowing through those output tubes,
giving higher gain and signal yield then previously.
Oh, what was that question again.
What, What,......??????
Speak up, it's hard to hear ya with everyone else talking at the same time.
Oh, got ya.....
They are called a Fluffer Nutter!!!!!!
Hey guys, simmer down a bit,......
What's a Fluffer Nutter,... is that what ya asked!!!!!!!!!!!!!!!!!!!
OK,.....
Well simply,.......
A Fluffer Nutter, is a nicer term for a former Expert, turned Turd Hugger!!!!!!!
Regards,
Rich Koerner,
Time Electronics.
http://www.timeelect.com
Specialists in Live Sound FOH Engineering,
Music & Studio Production,
Vintage Instruments, and Tube Amplifiers