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In Reply to: RE: The answer is no posted by tube wrangler on September 03, 2017 at 12:52:21
"the caps certainly steady
the voltage."
I thought you said that in a self-biased the bias varies according to musical demand.
When you said "No fixed bias amp has ever reproduced music in a convincing fashion because the bias doesn't vary according to musical demand." is that not the same as saying that in a self-biased circuit the bias does vary with the musical demand?
Which is it Dennis?
Does the bias stay steady or does the bias vary in a self-biased design?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Follow Ups:
Things that happen simultaneously in degrees aren't
well explained with absolutist calculations.
As usual, I will be going by actual performance.
Theory does come in, but ONLY when IT CONTRIBUTES.
-Dennis-
"Things that happen simultaneously in degrees aren't
well explained with absolutist calculations."Yes they are.
As the frequency falls the reactance of the capacitor increases and more of the total current flows through the resistor.
If we want 20Hz to flow only through the cap (and not cause current feedback to be applied to the tube) then we design the filter so that it's -3db point is a decade below 20Hz.
With a -3db point of 2Hz the phase and amplitude will be back to flat by 20Hz and virtually no AC will be flowing through the resistor.
What is the -3db point of the filter created by the (cathode resistor in parallel with the cathode impedance) and the value you picked for your cathode bypass cap.
If you give me the numbers I can show you how much of the AC is going through the resistor at any frequency you're interested in.
I can even tell you how much negative current feedback you are applying to the output tube at any frequency you're interested in and how much that increased the output tube's plate resistance and what that does to the damping factor of the amplifier.
All of these complex situations are easily explained with absolutist calculations.
BTW whether you know it or not it's that local current feedback that gives you the sound you are looking for. Your circuit design is technically wrong but you won't admit that. The fact is you're just building for a sound, an effect.
That's OK, we probably all do but most of us admit to it.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 09/04/17 09/04/17
as it is clearly better than the others...and by a long chalk.
Was LMAO a bit, we now have Energy Conservation being abused along with Transfer Efficiency...:)
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
speaking of Transfer eff, its a real phenomenon in that a tube driver uses a IT and good transfer eff is VERY important.
you could also apply this to the output transformer too :)
Lawrence
I understand your faith in being able to
calculate anything you want.
I don't tweak, period. I listen to the best
recordings available on the best equipment available.
I have owned movie theatres, and have designed and built
many a Stadium Theatre. Most theatres have bad sound--
but not very bad-- if the owners keep up with maintenance.
I have, over the years, enjoyed hearing and measuring
and observing in theatres, what it takes to totally
involve people in the presentation, and take the sound
system out of the equation-- make it so good that no one
notices it-- just what is happening.
My standard for HOME playback is the sound that is
factory encoded on L.P.'s, CD's, and on-line
Hi-Resolution downloads.
This is compared to studio master recordings, and
also to the systems that competitors have at audio
shows, and to people's own home systems.
I ask an amplifier to play back any and all of
these sources with verbatim accuracy-- at the point
that counts-- the speaker or headphone interface to
the listener..
I have found over the years, several solid state
amplifiers that will do this very well.
In order to have vacuum tubes do the same thing
well, the tube amp had to be condensed into a form
that would do this simply because all the other
tube amps I have applied, or heard-- have fallen
woefully short.
I haven't mentioned this lately on a forum, so
I'll just repeat it here: I NEVER build anything
unless I HAVE TO. I MUCH prefer to BUY it.
In the case of vacuum tube amplifiers, the
existing technology and construction methods
were absolutely hopeless. So, I FIXED that
problem. And, FIXED it is!
It's too bad that it's so controversial with you.
Actually, all it is is energy conservation applied
at every level, and superior layout and construction
methods, coupled with the use of really good parts.
Circuit operating values are super conservative
because I don't like the sound of stressed vacuum
tubes that every other tube amp I ever heard displays,
if played on large radiating area, point-source,
speakers that are over 100db/watt efficiency. The
GOOD amps-- including a few over 200 watt solid state
models, will play well on such speakers.
Nearly all tube amps that have been, or are being
built fall short in many ways.
If you're a modifier, you can rescue some older tube
amps by lowering voltages and currents, using better
parts, mounting iron on brass standoffs, and re-wiring
the whole thing..
If you do that, you're still coming up a bit short--
but much better--, so why not just start over and
design something that is sure to work?
It does!
-Dennis-
I think it depends on whether the foil hat is on or off.
.
Have Fun and Enjoy the Music
"Still Working the Problem"
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