By the time I was halfway and counted 31 gross errors, I knew you
hadn't written this, Cal. Not even you are that bolshie.

It is such a fabulous satire, I'm just green with envy that I didn't
thnk of it first!

Andre Jute

wrote:
D.T.N. WILLIAMSON AMPLIFIER

In the late 1940's, component Hi Fi was a hobby, much like amateur
radio. Amateur radio buffs built their own transmitters from parts
they bought in electronic distributor stores. A lot of these amateurs
had component sound systems as part of their overall short wave radio
systems. As industry changed over from wartime products to civilian
products, the electronic industry began making various parts for these
electronic distributors. Among these parts were audio amplifiers, raw
speakers and the like. Because there was a scarcity of parts in the
beginning, many small manufacturers found a ready market for their
electronic components. For many years, these small manufacturers
produced most of the audio electronic parts.

Magazines to serve the nascent component audio hobbyists appeared.
These magazines had similar format to the amateur radio magazines and
sometimes contained both amateur radio and audio gear. They published
numerous articles on various designs relating to electronic components.
Almost anyone could get published, as the magazines needed articles to
fill up their issues. This is why there are so many different audio
tube designs floating around. No one in the media world separated the
wheat from the chaff. As few people around today are familiar with the
technology of audio tube design, the chaff has puffed along with
reputable designs as "antique audio". There are a lot of bad ideas out
there along with the good ones. Let the buyer beware.
The Original Williamson Amplifier

Into this free wheeling media milieu, Williamson published an article
on audio amplifier design, which impressed everyone with the insight
into audio amplifier theory. Williamson gave certain criteria for
audio amplifier circuitry that broke new ground. Williamson's concepts
were valid, his articulation of his ideas into an amplifier were
seriously flawed. A basic component of his amplifier was the Partridge
transformer, a creation of Dr. Partridge. The Partridge output
transformer had a frequency response from 2 to 200,000 Hz. Its output
was 10 watts over most of the range. This quality level for an output
transformer was a milestone in the development of Hi Fi. Ten watts of
audio in 1949 was about the best that most were doing at the time. It
is not known that a Williamson produced amplifier was ever offered as a
unit to the American market. Williamson himself, an engineer employed
by a tube company never produced the amplifier at all. The Partridge
transformer was sold in America as a component and was available
through electronic distributors.

As originally configured, the amplifier was constructed on two chassis,
the power supply on one chassis, and the audio circuit on the other.
The recommended capacitors were huge oil filled, expensive units with
low capacitance. No chassis for the amplifier was available, and had
to be cobbled together by the constructor. It was all amateur stuff.
At the time, the entire industry was amateur stuff. Even so, the
quality of the new component audio was so superior to "set"
manufacturers like RCA, Philco and Zenith that the Hi Fi buffs lived in
the clouds, so to speak. Their gear was a quantum leap ahead of set
manufacturers.
The Williamson Theory

In 1950, Hi Fi bugs didn't know what "feedback" was. Any old theory of
feedback was an improvement over nothing. Williamson had phase
diagrams and curves to show that in order to place a stable feedback
loop around an amplifier, the problem was phase margins. In order to
assure stability, the output transformer should have a response from 2
to 200,000 Hz. This assured that the amplifier was stable in the audio
range of 20 to 20,000 Hz. This criteria had merit. Unfortunately,
Williamson did not carry his analysis far enough. Seemingly, he never
actually built a model of his amplifier. If he had, he would have
realized that there was more to it than an output transformer and
feedback loop. The only component in his design that met the 2-200,000
Hz. criteria was the output transformer. As presented, the Williamson
amplifier had a number of serious flaws. It was a good start, but it
was not thought out properly. When the author built a Williamson with
the Partridge transformer, he soon discovered these flaws. The
Williamson circuit and a critique will now be discussed.
The Williamson Circuit
We will discuss the circuit, block by block.

The Power Supply:

The Williamson power supply was built on a separate chassis. It had a
high voltage cord that connected it to the audio amplifier. Such
configurations aren't built any more. They are dangerous. Running a
400-volt DC power line for domestic use is against UL standards. The
seeming purpose of this set up was to isolate the power transformer
from the audio circuit (and output transformer). It has been shown
that there is no purpose in such a setup.

The circuit contained a 5U4 directly heated cathode as a rectifier.
The circuit was of the capacitor-input type and contained two chokes, a
5 Henry power choke and a 30 Henry smoothing choke. The filter
capacitors were oil filled 4 mf.400 volt units.

This supply had serious deficiencies. The audio circuit had a
direct-coupled first stage. On warm-up, the B+ supply initiated high
voltage to the bus before the output tubes warmed up. This caused a
very positive voltage to appear on the grid of the second stage during
warm-up. This caused current to flow from the second stage cathode to
the second stage grid. The likelihood of grid damage was high during
warm-up as grid wires are very small and won't carry much current.

When the Williamson was turned off, it fed a large very low frequency
power pulse to the speaker. Many Hi Fi speakers couldn't take this
very low frequency pulse and blew out. This turn off power pulse showed
that the power supply was unstable, poorly decoupled, poorly regulated
and prone to motor boating, a very nasty instability problem. The
capacitor-input system rendered marginal the use of the first choke as
a filter element. Capacitor input systems defeat the advantage of using
chokes in a power supply.

When the Williamson circuit was published, inexpensive electrolytic
capacitors were already available in the post war market. Oil
capacitors are very expensive per mf. and as obsolete as copper oxide
rectifiers. It was a poor choice for home use. Oil capacitors make
very poor power supply filters, for they lack enough capacity to do the
job. Electrolytic capacitors are much preferred in good designs, being
available in sizes to 500 mf. or more.

Continuing our critique of the Williamson amplifier, we turn now to the
amplifier circuit. The amplifier is composed of two sections; the
"front end" or voltage amplification and phase inversion section and
the power output section.
The voltage amplifier and phase inverter:

This section or block is composed of a voltage amplifier, phase
inverter and driver. The amplifier is a double triode, a 6SN7, one
section direct coupled to the phase inverter. Most of the front ends
at the time used pentode tubes like the 6SJ7as amplifiers. These tubes
had good amplification, but high distortion. Williamson's all triode
amplifier set a new standard for the industry (unfortunately not
followed by the Dyna). There are really no problems with Williamson's
triode input. It was a clean amplifier.

The phase inverter is another matter. Because good design demands a
"push-pull" power stage, the output tubes must be fed by phase
inversion of the driver. Good design mandates that the driver has
certain characteristics. The drive should be balanced amplitude wise
and phase wise. The careful phase inversion is the most difficult to
achieve. The Williamson phase inverter was a split load phase
inverter. The plate and cathode resisters of the second section of the
6SN7 were matched at 47 Kohm resisters. This balances the amplitude of
the inverted signal (as long as the load resisters don't drift with
time), but there is a hidden serious flaw, not dealt with by producers
of the Williamson amplifier.

The plate impedance and the cathode impedance are not of the same value
even though the load resisters are the same. This means that at high
frequency, the output of the phase inverter is no longer balanced. A
scope sampling the signal between the two driver signals shows the
discrepancy. This unbalance causes distortion. This distortion is
amplified by a negative feedback loop around the amplifier. If the
driver signals are tested with the feedback loop in place, the
unbalance is seen to be objectionably high, particularly at high
frequency. The poor phase inverter was the Achilles heel of the
Williamson circuit. Transient response, due to this defective phase
inverter is also poor. This type of distortion was not tested for at
the time the Williamson appeared. It is one of the reasons some claim
that negative feedback is "bad". Negative feedback is not bad if it is
around a clean amplifier. Negative feedback around a Williamson is a
mixed bag because of the flawed phase inverter.

There is another flaw in the front end. Examination shows that there
are two sets of coupling capacitors in the front end. This means that
when negative feedback is applied, the amplifier becomes unstable at
very low frequency because of the time constants of the capacitors. At
very low frequency a phase shift occurs of over 180 degrees around the
loop and oscillation can occur. This is aggravated because of the
poorly regulated power supply. At the time Williamson wrote his
article, capacitors had inductance. This limited the high frequency
response of the front end. 6SN7's have poor high frequency response
further limiting the high frequency response of the front end. The
front end began to roll above 30 Hz. The point is that Williamson's
Partridge transformer was not of much use in this kind of amplifier.
200,000 Hz is well beyond the response of the rest of the system.
The output stage:

In the American version of the Williamson, two 807's, triode connected
were connected in push pull and fed into the primary of the Partridge
output transformer. The pair of tubes were cathode biased (together)
with an unbypassed common cathode resister. This arrangement cost
output power and high frequency response. It is somewhat strange that
an engineer working for a tube manufacturer would recommend such an
output circuit. His company made KT66's, a beam power tube, ill suited
to be used as a triode. The 2A3, a power triode available at the time
was not used in the Williamson. Brook began making an amplifier with
the 2A3 shortly after the advent of the Williamson. The Miller effect
(grid to cathode capacitance) reduced the high frequency response of
the Williamson amplifier as the 6SN7's had fairly high plate impedance
for a triode.

The 807's were fed with 400 volts on the plates, which allowed them to
put out 10 watts RMS. This was in line with what some others were
doing in Hi Fi amplifiers, but less than the 20 watts output generally
available with 6L6's pentode connected. The distortion in the 6L6's
was higher, but with feedback, the distortion was acceptable. The real
advance made by Williamson was the design of an all triode amplifier.
It inspired others to meet its distortion performance, (with a
resistive load) poor though the Williamson was.

The input to the output stage had 1000-ohm suppressor resister in the
grid circuit. It also had a resister in the screen circuit, but the
screens were not regulated, and tied to t he plates.

This brings us to the operating characteristics of the 807's, triode
connected. Power triodes are voltage amplification devices. They try
to amplify voltage. With an output resistive load, this presents no
problem to the load line. By contract, power pentodes or beam power
tubes try to present a constant current to an output load. With a
resistive load, this also presents no problem to the load line.

The problem is that loudspeakers (the intended load of the output
transformer) are not a resistive load at most of the used frequencies
of a loudspeaker. When a loudspeaker is attached to an output
transformer instead of a resistive load, the load line of the output
tubes goes crazy, whether the tubes are triode or pentode connected.
Neither triode or pentode mode operate well with loudspeakers. This is
why all performance tests are carried out with resistive loads.

Keroes and Hafler invented the tapped screen mode of operation of
output tubes. By connecting the output tube screens to a tap at an
appropriate winding location, the output tubes put out constant power
into a load, rather than either constant voltage or constant current.

Distributed inductances and capacitances in the speaker circuit cause
the varying impedance of a loudspeaker over the used range (see:
Acoustical Engineering--Harry Olson, Chief Engineer, Audio, RCA. Harry
also taught acoustics at Columbia University when his book was
written.) Olson's book is the bible of the audio industry to this
day). As is easily shown, inductances and capacitances are reactive in
nature. They generate what is known as reactive power. You cannot
hear reactive power. What you hear with reactive power is phase shift,
which in stereo blurs the stereo effect.

By operating in a constant power mode, the output REAL power from a
loudspeaker is more constant. The frequency response is more linear.
It is obvious that "ultra-linear" (constant power out) is a better mode
of tube operation than either constant voltage or constant current.
When a passive crossover network is used in conjunction with a
loudspeaker system, the quality of sound degrades more with constant
voltage or current than with constant power ("ultra-linear") mode.

There are those presently practicing the art of audio tube design who
do not understand the nature of output tubes or circuits. This results
in a lot of false statements made around this subject. Given
everything else held constant, no triode or pentode tube operation
equals "ultra linear", (constant power) operation. The physics is
against it.
Some Observations

As mentioned elsewhere, Williamson was a tube engineer who worked for a
tube company. Williamson never made the amplifier bearing his name. If
he had, he would have made some modifications. Using chokes for
instance, and then negating their advantages by using a capacitance
input was rather silly. Williamson used a 5U4 power rectifier, which
was a directly heated cathode rectifier tube. This meant that the
amplifier tubes saw B+ before they were warmed up; bad for cathodes and
capacitors. The B+ (without load) was higher by far than normal
operation. Williamson's capacitors weren't rated for the voltage
surge.

Others subsequently used a mechanical switch to keep the high voltage
from the amplifier until the tubes warmed up. A far better circuit
uses a 5V4, an indirectly heated cathode rectifier, which does not draw
current before the rest of the circuit is ready as it takes it cathode
time to warm up too.

The Williamson feedback loop did not respond properly with crossover
networks in the output. Then too, the only component in the amplifier
that went to 200,000 Hz. was the output transformer. The Williamson
circuit did not meet Williamson's own criteria for open circuit
bandwidth. (Operation without feedback)

In 1947, speakers were mainly high efficiency types. This meant that
the bass resonance was high by modern standards, and the high
efficiency created a more ragged audio response curve. The electrical
impedance curve was more ragged also. However, a ten-watt amplifier
drove the speakers to acceptable levels. In today's world, ten watts
doesn't make it, as the speaker systems are no longer high efficiency.

Williamson used a two chassis system for his amplifier, believing that
magnetic coupling between transformers caused hum. Poor power supply
filtering caused Williamson's hum problems. No one produces two
chassis audio amplifiers today. There is no purpose.

It is curious that Williamson did not have his company design a good
triode equivalent to his triode connected tubes (KT66 or 807--U.S.)
The 2A3 was a better triode than triode connected KT66's. The Brook
amplifier that used 2A3's was a better amplifier than the Williamson.

There are those who will be talked into building this "antique". I
would suggest that if they build one, put it on the shelf and just look
at it. Williamsons and buggy whips don't have a use in the 21st.
Century. Also, as far as is known, no one is making the Partridge. In
today's world, it would cost too much for 10 watts out.

" wrote:

I assume that the windery which makes Partridge is either too small to
be able to bother with hobbyists or so large that they know it isn't
profitable. They do however make high-fidelity transformers and supply
them to small manufactories, or at least they did within recent memory.
For instance, a copy of the catalogue of La Maison de L'Audiophile in
Paris, no 24, undated but about 10-12 years old, list Partridge TK4519
output transformers suitable for 300B at 1900 francs and TK6241 power
trx for 2200 francs, also as the standard transformers in their
well-regarded Hiraga-inspired Legend 300B amp. The prices quoted are
similar to what La Maison charged for mid to high-level Tango iron.

HTH.

Andre Jute

Partridge is a name synonymous with hi-fi.

Seems like they have an almost invisible public profile, and maybe
they don't mind that, since with the name they have they'd probably have
enough old clients to keep them going without ever advertising.

If they tried going as big as Hammond, the quality might vanish.

Patrick Turner.

" wrote:

By the time I was halfway and counted 31 gross errors, I knew you
hadn't written this, Cal. Not even you are that bolshie.

It is such a fabulous satire, I'm just green with envy that I didn't
thnk of it first!

Andre Jute

Yes, and I fell in hook and line with me and thought he'd written all that
crap.

So I tried to say a few words in defense of old Willy, but anyway,
I guess there are always going to be ppl who poke sticks at good ideas,
and one can't ship to stay clean right through a voyage.
If the ship seems to be sailing slow, then someone else can jump over the
side to
clean off the barnacles; I'm headin off to the aft deck and a hammock.

Patrick Turner.



wrote:
D.T.N. WILLIAMSON AMPLIFIER

In the late 1940's, component Hi Fi was a hobby, much like amateur
radio. Amateur radio buffs built their own transmitters from parts
they bought in electronic distributor stores. A lot of these amateurs
had component sound systems as part of their overall short wave radio
systems. As industry changed over from wartime products to civilian
products, the electronic industry began making various parts for these
electronic distributors. Among these parts were audio amplifiers, raw
speakers and the like. Because there was a scarcity of parts in the
beginning, many small manufacturers found a ready market for their
electronic components. For many years, these small manufacturers
produced most of the audio electronic parts.

Magazines to serve the nascent component audio hobbyists appeared.
These magazines had similar format to the amateur radio magazines and
sometimes contained both amateur radio and audio gear. They published
numerous articles on various designs relating to electronic components.
Almost anyone could get published, as the magazines needed articles to
fill up their issues. This is why there are so many different audio
tube designs floating around. No one in the media world separated the
wheat from the chaff. As few people around today are familiar with the
technology of audio tube design, the chaff has puffed along with
reputable designs as "antique audio". There are a lot of bad ideas out
there along with the good ones. Let the buyer beware.
The Original Williamson Amplifier

Into this free wheeling media milieu, Williamson published an article
on audio amplifier design, which impressed everyone with the insight
into audio amplifier theory. Williamson gave certain criteria for
audio amplifier circuitry that broke new ground. Williamson's concepts
were valid, his articulation of his ideas into an amplifier were
seriously flawed. A basic component of his amplifier was the Partridge
transformer, a creation of Dr. Partridge. The Partridge output
transformer had a frequency response from 2 to 200,000 Hz. Its output
was 10 watts over most of the range. This quality level for an output
transformer was a milestone in the development of Hi Fi. Ten watts of
audio in 1949 was about the best that most were doing at the time. It
is not known that a Williamson produced amplifier was ever offered as a
unit to the American market. Williamson himself, an engineer employed
by a tube company never produced the amplifier at all. The Partridge
transformer was sold in America as a component and was available
through electronic distributors.

As originally configured, the amplifier was constructed on two chassis,
the power supply on one chassis, and the audio circuit on the other.
The recommended capacitors were huge oil filled, expensive units with
low capacitance. No chassis for the amplifier was available, and had
to be cobbled together by the constructor. It was all amateur stuff.
At the time, the entire industry was amateur stuff. Even so, the
quality of the new component audio was so superior to "set"
manufacturers like RCA, Philco and Zenith that the Hi Fi buffs lived in
the clouds, so to speak. Their gear was a quantum leap ahead of set
manufacturers.
The Williamson Theory

In 1950, Hi Fi bugs didn't know what "feedback" was. Any old theory of
feedback was an improvement over nothing. Williamson had phase
diagrams and curves to show that in order to place a stable feedback
loop around an amplifier, the problem was phase margins. In order to
assure stability, the output transformer should have a response from 2
to 200,000 Hz. This assured that the amplifier was stable in the audio
range of 20 to 20,000 Hz. This criteria had merit. Unfortunately,
Williamson did not carry his analysis far enough. Seemingly, he never
actually built a model of his amplifier. If he had, he would have
realized that there was more to it than an output transformer and
feedback loop. The only component in his design that met the 2-200,000
Hz. criteria was the output transformer. As presented, the Williamson
amplifier had a number of serious flaws. It was a good start, but it
was not thought out properly. When the author built a Williamson with
the Partridge transformer, he soon discovered these flaws. The
Williamson circuit and a critique will now be discussed.
The Williamson Circuit
We will discuss the circuit, block by block.

The Power Supply:

The Williamson power supply was built on a separate chassis. It had a
high voltage cord that connected it to the audio amplifier. Such
configurations aren't built any more. They are dangerous. Running a
400-volt DC power line for domestic use is against UL standards. The
seeming purpose of this set up was to isolate the power transformer
from the audio circuit (and output transformer). It has been shown
that there is no purpose in such a setup.

The circuit contained a 5U4 directly heated cathode as a rectifier.
The circuit was of the capacitor-input type and contained two chokes, a
5 Henry power choke and a 30 Henry smoothing choke. The filter
capacitors were oil filled 4 mf.400 volt units.

This supply had serious deficiencies. The audio circuit had a
direct-coupled first stage. On warm-up, the B+ supply initiated high
voltage to the bus before the output tubes warmed up. This caused a
very positive voltage to appear on the grid of the second stage during
warm-up. This caused current to flow from the second stage cathode to
the second stage grid. The likelihood of grid damage was high during
warm-up as grid wires are very small and won't carry much current.

When the Williamson was turned off, it fed a large very low frequency
power pulse to the speaker. Many Hi Fi speakers couldn't take this
very low frequency pulse and blew out. This turn off power pulse showed
that the power supply was unstable, poorly decoupled, poorly regulated
and prone to motor boating, a very nasty instability problem. The
capacitor-input system rendered marginal the use of the first choke as
a filter element. Capacitor input systems defeat the advantage of using
chokes in a power supply.

When the Williamson circuit was published, inexpensive electrolytic
capacitors were already available in the post war market. Oil
capacitors are very expensive per mf. and as obsolete as copper oxide
rectifiers. It was a poor choice for home use. Oil capacitors make
very poor power supply filters, for they lack enough capacity to do the
job. Electrolytic capacitors are much preferred in good designs, being
available in sizes to 500 mf. or more.

Continuing our critique of the Williamson amplifier, we turn now to the
amplifier circuit. The amplifier is composed of two sections; the
"front end" or voltage amplification and phase inversion section and
the power output section.
The voltage amplifier and phase inverter:

This section or block is composed of a voltage amplifier, phase
inverter and driver. The amplifier is a double triode, a 6SN7, one
section direct coupled to the phase inverter. Most of the front ends
at the time used pentode tubes like the 6SJ7as amplifiers. These tubes
had good amplification, but high distortion. Williamson's all triode
amplifier set a new standard for the industry (unfortunately not
followed by the Dyna). There are really no problems with Williamson's
triode input. It was a clean amplifier.

The phase inverter is another matter. Because good design demands a
"push-pull" power stage, the output tubes must be fed by phase
inversion of the driver. Good design mandates that the driver has
certain characteristics. The drive should be balanced amplitude wise
and phase wise. The careful phase inversion is the most difficult to
achieve. The Williamson phase inverter was a split load phase
inverter. The plate and cathode resisters of the second section of the
6SN7 were matched at 47 Kohm resisters. This balances the amplitude of
the inverted signal (as long as the load resisters don't drift with
time), but there is a hidden serious flaw, not dealt with by producers
of the Williamson amplifier.

The plate impedance and the cathode impedance are not of the same value
even though the load resisters are the same. This means that at high
frequency, the output of the phase inverter is no longer balanced. A
scope sampling the signal between the two driver signals shows the
discrepancy. This unbalance causes distortion. This distortion is
amplified by a negative feedback loop around the amplifier. If the
driver signals are tested with the feedback loop in place, the
unbalance is seen to be objectionably high, particularly at high
frequency. The poor phase inverter was the Achilles heel of the
Williamson circuit. Transient response, due to this defective phase
inverter is also poor. This type of distortion was not tested for at
the time the Williamson appeared. It is one of the reasons some claim
that negative feedback is "bad". Negative feedback is not bad if it is
around a clean amplifier. Negative feedback around a Williamson is a
mixed bag because of the flawed phase inverter.

There is another flaw in the front end. Examination shows that there
are two sets of coupling capacitors in the front end. This means that
when negative feedback is applied, the amplifier becomes unstable at
very low frequency because of the time constants of the capacitors. At
very low frequency a phase shift occurs of over 180 degrees around the
loop and oscillation can occur. This is aggravated because of the
poorly regulated power supply. At the time Williamson wrote his
article, capacitors had inductance. This limited the high frequency
response of the front end. 6SN7's have poor high frequency response
further limiting the high frequency response of the front end. The
front end began to roll above 30 Hz. The point is that Williamson's
Partridge transformer was not of much use in this kind of amplifier.
200,000 Hz is well beyond the response of the rest of the system.
The output stage:

In the American version of the Williamson, two 807's, triode connected
were connected in push pull and fed into the primary of the Partridge
output transformer. The pair of tubes were cathode biased (together)
with an unbypassed common cathode resister. This arrangement cost
output power and high frequency response. It is somewhat strange that
an engineer working for a tube manufacturer would recommend such an
output circuit. His company made KT66's, a beam power tube, ill suited
to be used as a triode. The 2A3, a power triode available at the time
was not used in the Williamson. Brook began making an amplifier with
the 2A3 shortly after the advent of the Williamson. The Miller effect
(grid to cathode capacitance) reduced the high frequency response of
the Williamson amplifier as the 6SN7's had fairly high plate impedance
for a triode.

The 807's were fed with 400 volts on the plates, which allowed them to
put out 10 watts RMS. This was in line with what some others were
doing in Hi Fi amplifiers, but less than the 20 watts output generally
available with 6L6's pentode connected. The distortion in the 6L6's
was higher, but with feedback, the distortion was acceptable. The real
advance made by Williamson was the design of an all triode amplifier.
It inspired others to meet its distortion performance, (with a
resistive load) poor though the Williamson was.

The input to the output stage had 1000-ohm suppressor resister in the
grid circuit. It also had a resister in the screen circuit, but the
screens were not regulated, and tied to t he plates.

This brings us to the operating characteristics of the 807's, triode
connected. Power triodes are voltage amplification devices. They try
to amplify voltage. With an output resistive load, this presents no
problem to the load line. By contract, power pentodes or beam power
tubes try to present a constant current to an output load. With a
resistive load, this also presents no problem to the load line.

The problem is that loudspeakers (the intended load of the output
transformer) are not a resistive load at most of the used frequencies
of a loudspeaker. When a loudspeaker is attached to an output
transformer instead of a resistive load, the load line of the output
tubes goes crazy, whether the tubes are triode or pentode connected.
Neither triode or pentode mode operate well with loudspeakers. This is
why all performance tests are carried out with resistive loads.

Keroes and Hafler invented the tapped screen mode of operation of
output tubes. By connecting the output tube screens to a tap at an
appropriate winding location, the output tubes put out constant power
into a load, rather than either constant voltage or constant current.

Distributed inductances and capacitances in the speaker circuit cause
the varying impedance of a loudspeaker over the used range (see:
Acoustical Engineering--Harry Olson, Chief Engineer, Audio, RCA. Harry
also taught acoustics at Columbia University when his book was
written.) Olson's book is the bible of the audio industry to this
day). As is easily shown, inductances and capacitances are reactive in
nature. They generate what is known as reactive power. You cannot
hear reactive power. What you hear with reactive power is phase shift,
which in stereo blurs the stereo effect.

By operating in a constant power mode, the output REAL power from a
loudspeaker is more constant. The frequency response is more linear.
It is obvious that "ultra-linear" (constant power out) is a better mode
of tube operation than either constant voltage or constant current.
When a passive crossover network is used in conjunction with a
loudspeaker system, the quality of sound degrades more with constant
voltage or current than with constant power ("ultra-linear") mode.

There are those presently practicing the art of audio tube design who
do not understand the nature of output tubes or circuits. This results
in a lot of false statements made around this subject. Given
everything else held constant, no triode or pentode tube operation
equals "ultra linear", (constant power) operation. The physics is
against it.
Some Observations

As mentioned elsewhere, Williamson was a tube engineer who worked for a
tube company. Williamson never made the amplifier bearing his name. If
he had, he would have made some modifications. Using chokes for
instance, and then negating their advantages by using a capacitance
input was rather silly. Williamson used a 5U4 power rectifier, which
was a directly heated cathode rectifier tube. This meant that the
amplifier tubes saw B+ before they were warmed up; bad for cathodes and
capacitors. The B+ (without load) was higher by far than normal
operation. Williamson's capacitors weren't rated for the voltage
surge.

Others subsequently used a mechanical switch to keep the high voltage
from the amplifier until the tubes warmed up. A far better circuit
uses a 5V4, an indirectly heated cathode rectifier, which does not draw
current before the rest of the circuit is ready as it takes it cathode
time to warm up too.

The Williamson feedback loop did not respond properly with crossover
networks in the output. Then too, the only component in the amplifier
that went to 200,000 Hz. was the output transformer. The Williamson
circuit did not meet Williamson's own criteria for open circuit
bandwidth. (Operation without feedback)

In 1947, speakers were mainly high efficiency types. This meant that
the bass resonance was high by modern standards, and the high
efficiency created a more ragged audio response curve. The electrical
impedance curve was more ragged also. However, a ten-watt amplifier
drove the speakers to acceptable levels. In today's world, ten watts
doesn't make it, as the speaker systems are no longer high efficiency.

Williamson used a two chassis system for his amplifier, believing that
magnetic coupling between transformers caused hum. Poor power supply
filtering caused Williamson's hum problems. No one produces two
chassis audio amplifiers today. There is no purpose.

It is curious that Williamson did not have his company design a good
triode equivalent to his triode connected tubes (KT66 or 807--U.S.)
The 2A3 was a better triode than triode connected KT66's. The Brook
amplifier that used 2A3's was a better amplifier than the Williamson.

There are those who will be talked into building this "antique". I
would suggest that if they build one, put it on the shelf and just look
at it. Williamsons and buggy whips don't have a use in the 21st.
Century. Also, as far as is known, no one is making the Partridge. In
today's world, it would cost too much for 10 watts out.

http://www.ivesonaudio.pwp.blueyonde...k/partrpwr.htm
http://www.ivesonaudio.pwp.blueyonde...k/partrchk.htm
http://www.ivesonaudio.pwp.blueyonde...k/partropt.htm

longer ago than I thought

Ian

Ian Iveson wrote:

http://www.ivesonaudio.pwp.blueyonde...k/partrpwr.htm
http://www.ivesonaudio.pwp.blueyonde...k/partrchk.htm
http://www.ivesonaudio.pwp.blueyonde...k/partropt.htm

longer ago than I thought

I wonder what's the situation 5 years later?

But the specs look fairly healthy.

Patrick Turner.



Ian

Patrick Turner wrote:

Ian Iveson wrote:

http://www.ivesonaudio.pwp.blueyonde...k/partrpwr.htm
http://www.ivesonaudio.pwp.blueyonde...k/partrchk.htm
http://www.ivesonaudio.pwp.blueyonde...k/partropt.htm

longer ago than I thought

I wonder what's the situation 5 years later?

But the specs look fairly healthy.

Patrick Turner.



Ian

I Googled Partridge for the hell of it. One hit was something called
'Shinrock' who seems to be in Der Vaterland.

Try
www.shinrock.com

The specs are quite impressive! Anybody know these guys?

Cheers, John Stewart