"Richard Harrison" bravely wrote to "All" (28 Feb 05 12:09:32)
--- on the heady topic of " Say what you mean."

RH From: (Richard Harrison)
RH Xref: aeinews rec.radio.amateur.antenna:26155

RH When there`s no signal input to a Class A amplifier, its power input
RH is volts x amps and its efficiency is zero. Maximunm undistorted output
RH requires 1/2 the d-c input to the stage. As this power exits the
RH stage, it cools as the remaining dissipation is only 1/2 the no-signal
RH dissipation.

I'm sorry but it is an erroneous conclusion to think it cools. Don't
you recall mentioning that the "average" voltage and current remains
the same? On the contrary, the stage would generate a little more heat
due to the a.c. losses incurred from a small, but non-negligible,
amount of internal resistance. That is because this internal loss
behaves just like a small resistance in series with the source of emf.


RH An amplifier can be a linear source without operating under Class A
RH conditions.

I would really find it instructive if you finished up replying to this
message with an example of a "linear" source not operating in Class A?

A*s*i*m*o*v

.... As I suspected, you're a rank sentimentalist! --Cpt. Louis Renault

Asimov wrote:
RH An amplifier can be a linear source without operating under Class A
RH conditions.

I would really find it instructive if you finished up replying to this
message with an example of a "linear" source not operating in Class A?

Richard may be referring to Class AB push-pull where
the source is more than one device.
--
73, Cecil http://www.qsl.net/w5dxp


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Cecil, W5DXP wrote:
"Richard may be referring to Class AB push-pull where the source is more
than one device,"

Push-pull works to eliminate harmonics without filters. In my Kenwood
TS-130S, the push-pull devices are 2SC2290*J`s, if my squint is right.
Pc=175 (W), VCBo=45 (V), IC=20 (A), etc.

Best regards, Richard Harrison, KB5WZI

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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