Post by l***@aol.comPost by Dave MooreIf you want to give me shit on political or OT issues fine,
but I take exception to misquotes on technical matters.
Dave, you probably know a lot more about these issues than anything
related to tube amplifiers, by any technical yardstick, if your posts
are the evidence. As I have mentioned before, you are usually as full
of it as a Christmas goose. :-)
DM
yes you have, and you were full of it then also.
Funny,, I don't see anyone else that's *actually*
knowledgeable about amps backing you up with your
assertions. Doesn't that strike you as a bit peculiar?
What are you anyway,, another AOL troll or something?
care to cite your credentials?
Post by l***@aol.comConsider learning something about AB1 dissipation.
Well, isn't that cute,, a nice snitty little remark
with no information offered.
Not so surprising however as
I went through the AGA archives looking for anything
technical you've ever posted and simply got tired of
looking for anything significant that you've ever posted
that might indicate that you know your ass from up.
All I found was a bunch of little snit assed remarks
to people and a few mentions of different bias classes
with no explanations of the bias classes beyond the
name dropping of them.
Now if you think otherwise,, perhaps you can
post a link to anything technical you've ever posted
that has nay meat in it and save me the trouble
of wading through a mountain of ankle biting
and operating class name dropping.
Concerning the power dissipation of tubes in an
AB1 output section biased slightly on the hot side
--------------------------------------------------------------------
Sure, they'll dissipate slightly more power
if the amp is biased hotter. Not enough more to be
of any significant consequence or problem however.
Why, because the dynamic dissipation of the
output tubes is defined by the B+ value used
and the value of load impedance used, not the
bias point. ( within limits of course)
The bias point ( within practical values) has little
effect on the *dynamic* dissipation of the output
tubes. It affects mainly the *static* dissipation.
There will however be a small amount of
power unattainable as the *active* input voltage
swing will be reduced by the amount of underbias.
Lets say (using arbitrary values) that you were to
bias the grids at -45 volts instead of -55 volts.
At -55V, the output tubes will
respond to a peak to peak input signal of 110 volts
before saturation occurs.
Whereas if the bias was -45 volts, the output tubes
will only respond to a 90VPP signal before saturation
occurs. This translates into a slightly reduced voltage
swing at the output.
However in terms of output power, this small
loss isn't that significant audibly.
A small price to pay for the reduction
of third harmonic distortion ( if that's what one likes)
You have to remember that in dynamic operation,
only one tube is on at a time anyway, so the only
increase in tube dissipation for dynamic operation
will be for a *very brief* period of time when both
halves are conducting.
yeah,, that's right,, if you bias a bit on the hot side,
the operation for very small signals will be AB2.
Then as the signal level increases,
due to some (very slight) grid leakage and also the fact
that the drive signal from the phase splitter isn't perfectly
symetrical, (DC component), an added negative bias
accumulates on the grid coupling caps which pushes
the class back to AB1.
Then if you hard clip the amp to where the drive signal
exceeds 0 volts,, the grids on the output tubes
will be forward biased and forward conduction of the
grids will occur.
When this happens, the grid coupling caps *really*
take on an additive negative charge *big time*
and the resulting debiasing effect can push the
output section all the way into Class C
(as long as the amp is being hard clipped that is)
That's right Virginia,, the class of operation gets
jacked around depending on signal size.
Post by l***@aol.comThe fact that you
may get away with believing & doing things wrong, even if it works for
you all your life, doesn't make you right about anything.
DM
Oh, I see,, the fact that it works, doesn't mean it works.
That's really rich.
No Motherboard or Microprocessor manufacturer
ever recommends to overclock,,, but people do it
all the time. Fact of life. Get used to it.
When working at Memorex, we had an entire
department devoted to testing parts to see if they
were up to the standards specified by their specs.
99% of the time, parts tested
exceeded their specs by 10-20% or more.
Not too surprising when one considers how the specs
for parts a made.
First the limits are found, then the specs are usually
spec'd below their tested failure values.
Any company that doesn't
over spec it's parts would be just downright foolish.
Although likewise it would be foolish for a designer
to assume this,, so generally designers will design
a bit more tolerance into the design.
so,, the product usually ends up with a good bit of
headroom that the brave can sometimes exploit.
Do you think that a mosfet that is rated for 800 volts will
avalanche at exactly 800 volts. I have yet to find one that will.
However, this is optional for the manufacturer. They can
specify parts in anyway they choose. It's not written in
stone.
However, it should be noted that this thread was about
El34's and the plates on EL34's tend to glow rather
soon whereas I usually use more scientific methods
to bias 6L6's.
Dave Moore True expert