Asimov wrote:
"I`m sorry but it is an erroneous conclusion to think it cools (when
signal exits)."

The Class A amplifier gets all its power from the d-c supply and it is
constant, signal or no signal. With signal power output, some of the
power in exits to the load.

I`ll use Cecil, W5DXP`s argument. Energy must be conserved. Energy in
equals energy out. If some goes to a load it does not stay within the
amplifier to make feat.

Asimov also wrote:
"---linear source not operating Class A?"

I`ll give an example. The Class B amplifier is biased near current
cut-off. Current is near zero when the signal is. Yet, output can
favorably vie with that from a Class A amplifier for purity. I learned
that nearly 60 years ago when I built my first 6N7 phonograph amplifier.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
I`ll use Cecil, W5DXP`s argument. Energy must be conserved. Energy in
equals energy out. If some goes to a load it does not stay within the
amplifier to make heat.

From "Electronic Fundamentals and Applications" by
John D. Ryder, regarding Class-A amplifiers:
"As the a-c output increases, the plate loss
decreases and the tube runs cooler."
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil Moore wrote:
Richard Harrison wrote:

I`ll use Cecil, W5DXP`s argument. Energy must be conserved. Energy in
equals energy out. If some goes to a load it does not stay within the
amplifier to make heat.


From "Electronic Fundamentals and Applications" by
John D. Ryder, regarding Class-A amplifiers:
"As the a-c output increases, the plate loss
decreases and the tube runs cooler."


This is why the load must be matched to the amp. Anyone who has fried a
final will tell you so.
Been there, Done that, Got the bottles to prove it.

Dave WD9BDZ

"Cecil Moore" bravely wrote to "All" (01 Mar 05 09:21:18)
--- on the heady topic of " Say what you mean."

CM From: Cecil Moore
CM Xref: aeinews rec.radio.amateur.antenna:26191

CM From "Electronic Fundamentals and Applications" by
CM John D. Ryder, regarding Class-A amplifiers:
CM "As the a-c output increases, the plate loss
CM decreases and the tube runs cooler."

harmonic generation...

A*s*i*m*o*v

.... Be nice to your kids. They'll choose your nursing home.

Asimov wrote:
harmonic generation...

Why do the instructions on my stereo amp warn against
running the amp with no speakers attached?
--
73, Cecil http://www.qsl.net/w5dxp


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"Cecil Moore" bravely wrote to "All" (02 Mar 05 07:55:04)
--- on the heady topic of " Say what you mean."

CM From: Cecil Moore
CM Xref: aeinews rec.radio.amateur.antenna:26244

CM Asimov wrote:
harmonic generation...

CM Why do the instructions on my stereo amp warn against
CM running the amp with no speakers attached?

Because then the screen tries to carry the plate signal, the reactance
in the output transformer is not damped, and because a tube is
sensitive to voltage, this quickly leads to a molten hole in the side?
Watts to plasma.

A*s*i*m*o*v

Asimov wrote:

"Cecil Moore" bravely wrote:
CM Why do the instructions on my stereo amp warn against
CM running the amp with no speakers attached?

Because then the screen tries to carry the plate signal, the reactance
in the output transformer is not damped, and because a tube is
sensitive to voltage, this quickly leads to a molten hole in the side?
Watts to plasma.

Sorry, it's solid state - no screen. Let's face it - unloaded
amplifiers tend to burn up no matter what class they are running.
--
73, Cecil http://www.qsl.net/w5dxp

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"Cecil Moore" bravely wrote to "All" (02 Mar 05 20:05:49)
--- on the heady topic of " Say what you mean."

CM From: Cecil Moore
CM Xref: aeinews rec.radio.amateur.antenna:26289

CM Asimov wrote:
Watts to plasma.

CM Sorry, it's solid state - no screen. Let's face it - unloaded
CM amplifiers tend to burn up no matter what class they are running.

Why don't you repeat that to the folk who think their amp cools when
it outputs watts?

A*s*i*m*o*v

.... New computer? But I like my vacuum tubes... They keep me warm.

"Richard Harrison" bravely wrote to "All" (01 Mar 05 08:29:27)
--- on the heady topic of " Say what you mean."

RH From: (Richard Harrison)
RH Xref: aeinews rec.radio.amateur.antenna:26189

RH The Class A amplifier gets all its power from the d-c supply and it is
RH constant, signal or no signal. With signal power output, some of the
RH power in exits to the load.

Let's look at it from the dynamic point of view. When there is no
signal the circumstances are as you describe. When the signal swing
turns the device nearly OFF there is a maximum voltage across the
device but the current is a minimum or close to zero.

Conversely when the signal swings in the opposite polarity the device
turns ON hard but the voltage is at a minimum or near zero too. In
either case the "ideal" device dissipates no extra power because the
two products are always zero. In fact the power difference is
always zero, so there is no reason for the device to cool.

However, no device is ideal, it has losses, and generates harmonics.
If the rectification is such that the average current decreases then
the device will cool. There is a gotcha however, because the harmonics
rob power from the desired output.


RH I`ll use Cecil, W5DXP`s argument. Energy must be conserved. Energy in
RH equals energy out. If some goes to a load it does not stay within the
RH amplifier to make feat.

As you said, if the amplifier dissipates 100W when idle and it can
drive 100W into a load then the power source will still supply 100W
when so doing, of course being an ideal device and neglecting all
other losses. It is easy to test by paralleling a substantial
capacitance and measuring the supply current before the cap. The
current should remain the same or rise only very slightly.


RH Asimov also wrote:
RH "---linear source not operating Class A?"

RH I`ll give an example. The Class B amplifier is biased near current
RH cut-off. Current is near zero when the signal is. Yet, output can
RH favorably vie with that from a Class A amplifier for purity. I learned
RH that nearly 60 years ago when I built my first 6N7 phonograph
RH amplifier.

Class B is hardly linear if it only amplifies 1/2 of the sinewave.
Time for our periodic 10 year review. g

A*s*i*m*o*v

.... That's a cute trick.

Asimov wrote:
In fact the power difference is
always zero, so there is no reason for the device to cool.

Here's the reason the device cools under load.

Plate loss = Eb*Ib - Ip^2*RL

With no signal, the plate loss is Eb*Ib. When
the signal is increased from zero, any power
delivered to the load is subtracted from Eb*Ib,
thus causing the device to cool.
--
73, Cecil http://www.qsl.net/w5dxp


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