[Ian Bell[_2_]]

I have managed to contact Alan Kimmel who kindly passed on the info he
has about the origins of the mu-follower. He says:

"A mu stage and a mu follower are not exactly the same: "Mu follower" is
the name coined by Mr. Christopher Paul to describe a mu-mode stage that
has a triode tube on top.

"Mu stage" is the name for a mu-mode stage having a pentode or a MOSFET
on top. Having a high gain device on top such as a pentode or MOSFET
allows the "bottom" tube to attain 100% of its rated mu (or very close
to rated mu).

A few months after my Mu Stage article appeared in Glass Audio magazine,
Mr. Tim Fiddler of London, England contacted me and informed me that the
Mu Follower circuit idea had appeared as Fig. (b) on page 351 in
Electronic & Radio Engineer, Sept. 1958. On page 554 of Wireless
World, Nov. 1962, is a circuit similar to the Mu Stage. "

So, does anyone have either of these two magazines??

Cheers

Ian

[Patrick Turner]

On Oct 8, 12:39*am, Ian Bell wrote:
I have managed to contact Alan Kimmel who kindly passed on the info he
has about the origins of the mu-follower. He says:

"A mu stage and a mu follower are not exactly the same: "Mu follower" is
the name coined by Mr. Christopher Paul to describe a mu-mode stage that
has a triode tube on top.

"Mu stage" is the name for a mu-mode stage having a pentode or a MOSFET
on top. *Having a high gain device on top such as a pentode or MOSFET
allows the "bottom" tube to attain 100% of its rated mu (or very close
to rated mu).

A few months after my Mu Stage article appeared in Glass Audio magazine,
Mr. Tim Fiddler of London, England contacted me and informed me that the
Mu Follower circuit idea had appeared as Fig. (b) on page 351 in
Electronic & Radio Engineer, Sept. 1958. * On page 554 of Wireless
World, Nov. 1962, is a circuit similar to the Mu Stage. "

So, does anyone have either of these two magazines??

Cheers

Ian

The mu-follower should be called the µ-follower because the gain
approaches the µ of the tube which is the gain without any current
change, ie, when the tube operates as a purely electrostatic device.

But I also would think the mu-foll stage was invented before WW2 and
it was known as a "bootstrapped follower" which of course it is. It
rarely ever was used in common equipments because the bean counters
could never allow 2 tubes to be used where one would do, just so some
1941 nerd wanted THD to be a bit lower. Myabe if we were to search the
old hard cover text books used to teach electronics students the
basics and not so basic in 1941 we might stumble over samples of the
mu-foll connection, with questions about such samples asked at the end
of chapters, for example, how to calculate the gain, and the Rout.

Patrick Turner.

[Ian Bell[_2_]]

Patrick Turner wrote:
On Oct 8, 12:39 am, Ian Bell wrote:
I have managed to contact Alan Kimmel who kindly passed on the info he
has about the origins of the mu-follower. He says:

"A mu stage and a mu follower are not exactly the same: "Mu follower" is
the name coined by Mr. Christopher Paul to describe a mu-mode stage that
has a triode tube on top.

"Mu stage" is the name for a mu-mode stage having a pentode or a MOSFET
on top. Having a high gain device on top such as a pentode or MOSFET
allows the "bottom" tube to attain 100% of its rated mu (or very close
to rated mu).

A few months after my Mu Stage article appeared in Glass Audio magazine,
Mr. Tim Fiddler of London, England contacted me and informed me that the
Mu Follower circuit idea had appeared as Fig. (b) on page 351 in
Electronic & Radio Engineer, Sept. 1958. On page 554 of Wireless
World, Nov. 1962, is a circuit similar to the Mu Stage. "

So, does anyone have either of these two magazines??

Cheers

Ian

The mu-follower should be called the µ-follower because the gain
approaches the µ of the tube which is the gain without any current
change, ie, when the tube operates as a purely electrostatic device.

But I also would think the mu-foll stage was invented before WW2 and
it was known as a "bootstrapped follower" which of course it is.

I am not so sure it was so early. I have a 1948 Wireless World in which
an article staes 'the cascode is 10 years old' and refers to an article
from 1938 where it was apparently first described. The mu follower must
be some time after that. The White follower patent is dated September
1944 and I am pretty sure that precedes the mu follower.

It
rarely ever was used in common equipments because the bean counters
could never allow 2 tubes to be used where one would do, just so some
1941 nerd wanted THD to be a bit lower. Myabe if we were to search the
old hard cover text books used to teach electronics students the
basics and not so basic in 1941 we might stumble over samples of the
mu-foll connection, with questions about such samples asked at the end
of chapters, for example, how to calculate the gain, and the Rout.


Nice thought but I suspect unlikely. The cascode was invented to get
decent gain at very high frequencies principally for the development of
radar and low distortion and low output impedance were not important
criteria - gain was important and the cascode has a lot more gain than
the mu follower. Nonetheless I'll keep my eyes peeled on the end of
chapter questions in those old books.


Cheers

ian
Patrick Turner.

[Patrick Turner]

On Oct 9, 3:59*am, Ian Bell wrote:
Patrick Turner wrote:
On Oct 8, 12:39 am, Ian Bell wrote:
I have managed to contact Alan Kimmel who kindly passed on the info he
has about the origins of the mu-follower. He says:

"A mu stage and a mu follower are not exactly the same: "Mu follower" is
the name coined by Mr. Christopher Paul to describe a mu-mode stage that
has a triode tube on top.

"Mu stage" is the name for a mu-mode stage having a pentode or a MOSFET
on top. *Having a high gain device on top such as a pentode or MOSFET
allows the "bottom" tube to attain 100% of its rated mu (or very close
to rated mu).

A few months after my Mu Stage article appeared in Glass Audio magazine,
Mr. Tim Fiddler of London, England contacted me and informed me that the
Mu Follower circuit idea had appeared as Fig. (b) on page 351 in
Electronic & Radio Engineer, Sept. 1958. * On page 554 of Wireless
World, Nov. 1962, is a circuit similar to the Mu Stage. "

So, does anyone have either of these two magazines??

Cheers

Ian

The mu-follower should be called the µ-follower because the gain
approaches the µ of the tube which is the gain without any current
change, ie, when the tube operates as a purely electrostatic device.

But I also would think the mu-foll stage was invented before WW2 and
it was known as a "bootstrapped follower" which of course it is.

I am not so sure it was so early. I have a 1948 Wireless World in which
an article staes 'the cascode is 10 years old' and refers to an article
from 1938 where it was apparently first described. The mu follower must
be some time after that. The White follower patent is dated September
1944 and I am pretty sure that precedes the mu follower.

* It

rarely ever was used in common equipments because the bean counters
could never allow 2 tubes to be used where one would do, just so some
1941 nerd wanted THD to be a bit lower. Myabe if we were to search the
old hard cover text books used to teach electronics students the
basics and not so basic in 1941 we might stumble over samples of the
mu-foll connection, with questions about such samples asked at the end
of chapters, for example, how to calculate the gain, and the Rout.

Nice thought but I suspect unlikely. The cascode was invented to get
decent gain at very high frequencies principally for the development of
radar and low distortion and low output impedance were not important
criteria - gain was important and the cascode has a lot more gain than
the mu follower. Nonetheless I'll keep my eyes peeled on the end of
chapter questions in those old books.

Cheers

ian

The cascode is an entirely different animal to a mu-follower.
With cascode, you can use two triodes to mimic a pentode. Cascode only
works best if the RL is very high, and in RF circuits if often is
because a tuned LC circuit is the load.
Therefore you get some gain in the bottom triode of the series pair.
But gain in the bottom triode is not really wanted sometimes because
the use of cascode without bottom tube gain is often done to just to
avoid the Miller C which you would get using just one triode in a
common cathode amp.

In cascode the THD of the bottom triode adds to that of the top
triode, so the circuit has to be used carefully if low THD is wanted.
Cascode is also a quiet circuit; presumably less noise than a pentode,
so its a good RF front end stage.

I use cascode for an MC phono input stage using a 2SK369 driving the
cathode of a triode such as 6DJ8, or 12AT7 or trioded 6EJ7.
Another way to avoid Miller is to have a grounded grid triode driven
at its cathode by a CF with the two commoned cathodes taken to a CCS.
At RF the CCS is not used, and instead there is an RF choke.

Patrick Turner.

[vtc]

Ian Bell wrote:
I have managed to contact Alan Kimmel who kindly passed on the info he
has about the origins of the mu-follower. He says:

"A mu stage and a mu follower are not exactly the same: "Mu follower" is
the name coined by Mr. Christopher Paul to describe a mu-mode stage that
has a triode tube on top.

"Mu stage" is the name for a mu-mode stage having a pentode or a MOSFET
on top. Having a high gain device on top such as a pentode or MOSFET
allows the "bottom" tube to attain 100% of its rated mu (or very close
to rated mu).

A few months after my Mu Stage article appeared in Glass Audio magazine,
Mr. Tim Fiddler of London, England contacted me and informed me that the
Mu Follower circuit idea had appeared as Fig. (b) on page 351 in
Electronic & Radio Engineer, Sept. 1958. On page 554 of Wireless
World, Nov. 1962, is a circuit similar to the Mu Stage. "

So, does anyone have either of these two magazines??

Cheers

Ian

Could it be that the original name for this circuit is a Balanced Direct
and Alternating Current Amplifier (Maurice Artzt, Radio Corporation of
America, February 9, 1943, Patent 2310342).

[Patrick Turner]

On Oct 11, 6:39*am, vtc wrote:
Ian Bell wrote:
I have managed to contact Alan Kimmel who kindly passed on the info he
has about the origins of the mu-follower. He says:

"A mu stage and a mu follower are not exactly the same: "Mu follower" is
the name coined by Mr. Christopher Paul to describe a mu-mode stage that
has a triode tube on top.

"Mu stage" is the name for a mu-mode stage having a pentode or a MOSFET
on top. *Having a high gain device on top such as a pentode or MOSFET
allows the "bottom" tube to attain 100% of its rated mu (or very close
to rated mu).

A few months after my Mu Stage article appeared in Glass Audio magazine,
Mr. Tim Fiddler of London, England contacted me and informed me that the
Mu Follower circuit idea had appeared as Fig. (b) on page 351 in
Electronic & Radio Engineer, Sept. 1958. * On page 554 of Wireless
World, Nov. 1962, is a circuit similar to the Mu Stage. "

So, does anyone have either of these two magazines??

Cheers

Ian

Could it be that the original name for this circuit is a Balanced Direct
and Alternating Current Amplifier (Maurice Artzt, Radio Corporation of
America, February 9, 1943, Patent 2310342).- Hide quoted text -

- Show quoted text -

The mu-follower does not appear to be a balanced circuit, either at dc
or ac operation.

But the old McGraw-Hill hard cover text books about high falootin amp
ideas from about 1943 would have a circuit called the "bootstrapped
follower" which is how a mu-follower should be described.

Just about every possible way tubes could be configured has already
been done by someone somewhere and quite a long while ago. If you read
the early copies after 1917 of Wireless World you'll see a
smorgasboard of the circuit types worth remembering.

Oscilloscopes date back a heck of a long time ago, as does the long
tail differential pair, or balanced differential amp.
Hardly anyone except a Government Dept or the Military could ever get
access to any of it.

The imagination of what could be done with electronics preceded the
development of suitable circuits and tubes and other bits. I recall
there were guys sitting around in cafes scribbling circuits on table
napkins to describe digital ways of transfering info in 1933.

Much early circuit developments have been entirely forgotten,
especially the complex stuff for industry, rocket guidance, computers,
machine controls, and early versions of oscillators for synthesizing
music etc. Sometimes people have brought me some damn thing made in
about 1942, and just what it does is a mystery, and tracing the
circuit to produce a schematic would take at least a week I don't
have. So the person just puts it in their garage for 20 more years,
then he dies, and their relatives just send it to the tip.

But the mu-follower is a nice simple linear gain circuit with high Z
in, low Z out, and where the heat dissipation from a pair of triodes
is halved because you have then in series without heat loss in dc load
resistors.

Patrick Turner.

[Ian Bell[_2_]]

vtc wrote:
Ian Bell wrote:
I have managed to contact Alan Kimmel who kindly passed on the info he
has about the origins of the mu-follower. He says:

"A mu stage and a mu follower are not exactly the same: "Mu follower"
is the name coined by Mr. Christopher Paul to describe a mu-mode stage
that has a triode tube on top.

"Mu stage" is the name for a mu-mode stage having a pentode or a
MOSFET on top. Having a high gain device on top such as a pentode or
MOSFET allows the "bottom" tube to attain 100% of its rated mu (or
very close to rated mu).

A few months after my Mu Stage article appeared in Glass Audio
magazine, Mr. Tim Fiddler of London, England contacted me and informed
me that the Mu Follower circuit idea had appeared as Fig. (b) on page
351 in Electronic & Radio Engineer, Sept. 1958. On page 554 of
Wireless World, Nov. 1962, is a circuit similar to the Mu Stage. "

So, does anyone have either of these two magazines??

Cheers

Ian

Could it be that the original name for this circuit is a Balanced Direct
and Alternating Current Amplifier (Maurice Artzt, Radio Corporation of
America, February 9, 1943, Patent 2310342).


Nice try, close but no cigar. That patent is well known to be and is an
SRPP but not a mu follower.

Cheers

Ian

[Ian Bell[_2_]]

Patrick Turner wrote:
On Oct 11, 6:39 am, vtc wrote:
Ian Bell wrote:
I have managed to contact Alan Kimmel who kindly passed on the info he
has about the origins of the mu-follower. He says:
"A mu stage and a mu follower are not exactly the same: "Mu follower" is
the name coined by Mr. Christopher Paul to describe a mu-mode stage that
has a triode tube on top.
"Mu stage" is the name for a mu-mode stage having a pentode or a MOSFET
on top. Having a high gain device on top such as a pentode or MOSFET
allows the "bottom" tube to attain 100% of its rated mu (or very close
to rated mu).
A few months after my Mu Stage article appeared in Glass Audio magazine,
Mr. Tim Fiddler of London, England contacted me and informed me that the
Mu Follower circuit idea had appeared as Fig. (b) on page 351 in
Electronic & Radio Engineer, Sept. 1958. On page 554 of Wireless
World, Nov. 1962, is a circuit similar to the Mu Stage. "
So, does anyone have either of these two magazines??
Cheers
Ian
Could it be that the original name for this circuit is a Balanced Direct
and Alternating Current Amplifier (Maurice Artzt, Radio Corporation of
America, February 9, 1943, Patent 2310342).- Hide quoted text -

- Show quoted text -

The mu-follower does not appear to be a balanced circuit, either at dc
or ac operation.

But the old McGraw-Hill hard cover text books about high falootin amp
ideas from about 1943 would have a circuit called the "bootstrapped
follower" which is how a mu-follower should be described.


You are right about the bootstrapping. I have had a further discussion
with Alan Kimmel and he tells me the article in the Electronics and
Radio Engineer is entitled "Bootstrap Circuit Technique". I have asked
my local library to get me a photocopy of the article.


Just about every possible way tubes could be configured has already
been done by someone somewhere and quite a long while ago. If you read
the early copies after 1917 of Wireless World you'll see a
smorgasboard of the circuit types worth remembering.

Oscilloscopes date back a heck of a long time ago, as does the long
tail differential pair, or balanced differential amp.


The long tailed pair was invented by Blumlein when he was at EMI just
before WW2. he patents are available now but whether they were at the
time is another matter.

Cheers

Ian


Hardly anyone except a Government Dept or the Military could ever get
access to any of it.

The imagination of what could be done with electronics preceded the
development of suitable circuits and tubes and other bits. I recall
there were guys sitting around in cafes scribbling circuits on table
napkins to describe digital ways of transfering info in 1933.

Much early circuit developments have been entirely forgotten,
especially the complex stuff for industry, rocket guidance, computers,
machine controls, and early versions of oscillators for synthesizing
music etc. Sometimes people have brought me some damn thing made in
about 1942, and just what it does is a mystery, and tracing the
circuit to produce a schematic would take at least a week I don't
have. So the person just puts it in their garage for 20 more years,
then he dies, and their relatives just send it to the tip.

But the mu-follower is a nice simple linear gain circuit with high Z
in, low Z out, and where the heat dissipation from a pair of triodes
is halved because you have then in series without heat loss in dc load
resistors.

Patrick Turner.

[John Byrns]

In article
,
Patrick Turner wrote:


The imagination of what could be done with electronics preceded the
development of suitable circuits and tubes and other bits. I recall
there were guys sitting around in cafes scribbling circuits on table
napkins to describe digital ways of transfering info in 1933.

Patrick, I didn't think you were old enough to recall seeing those guys
doodling on table napkins in 1933?

Much early circuit developments have been entirely forgotten,
especially the complex stuff for industry, rocket guidance, computers,
machine controls, and early versions of oscillators for synthesizing
music etc. Sometimes people have brought me some damn thing made in
about 1942, and just what it does is a mystery, and tracing the
circuit to produce a schematic would take at least a week I don't
have. So the person just puts it in their garage for 20 more years,
then he dies, and their relatives just send it to the tip.

But the mu-follower is a nice simple linear gain circuit with high Z
in, low Z out, and where the heat dissipation from a pair of triodes
is halved because you have then in series without heat loss in dc load
resistors.

"Halved"? Doesn't the "mu-follower" still retain one of the two "dc
load resistors" and its attendant "heat loss"? The plate resistor for
the common cathode stage is not eliminated in the "mu-follower" circuit,
it's simply bootstrapped to increase its impedance for the AC signal.

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Patrick Turner]

On Oct 12, 1:49*am, John Byrns wrote:
In article
,
*Patrick Turner wrote:



The imagination of what could be done with electronics preceded the
development of suitable circuits and tubes and other bits. I recall
there were guys sitting around in cafes scribbling circuits on table
napkins to describe digital ways of transfering info in 1933.

Patrick, I didn't think you were old enough to recall seeing those guys
doodling on table napkins in 1933?

Ah, its good to see your're not asleep John.

Of course I didn't see the guys a'doodlin' in some cafe in 1933, but I
read somewhere that the guys who invented early computers were
thinking about it in the early 30s. They lamented the fact that huge
numbers of tubes would be needed, and maybe the resulting computer
wouldn't do much. But just after WW2, thoughts about pooters had
matured a little, then someone invented a transistor, and the rest is
history.


Much early circuit developments have been entirely forgotten,
especially the complex stuff for industry, rocket guidance, computers,
machine controls, and early versions of oscillators for synthesizing
music etc. Sometimes people have brought me some damn thing made in
about 1942, and just what it does is a mystery, and tracing the
circuit to produce a schematic would take at least a week I don't
have. So the person just puts it in their garage for 20 more years,
then he dies, and their relatives just send it to the tip.

But the mu-follower is a nice simple linear gain circuit with high Z
in, low Z out, and where the heat dissipation from a pair of triodes
is halved because you have then in series without heat loss in dc load
resistors.

"Halved"? *Doesn't the "mu-follower" still retain one of the two "dc
load resistors" and its attendant "heat loss"? *The plate resistor for
the common cathode stage is not eliminated in the "mu-follower" circuit,
it's simply bootstrapped to increase its impedance for the AC signal.

Not really, and you split hairs.

A typical 2 stage amp using 2 halves of a 6SN7 will have 47k loads
with about 1/2 the B+ across each; one is the anode load, and one is
the cathode load of the CF. So if Ia = 3mA in each triode and B+ is
300V, then you have 300V x 6mA.

For a mu-foll, you would not have a 47k between the 2 1/2 triodes
which are in series. You would have maybe 8k2.
And Ia through the lot might be 3mA, so you have 300V x 3mA.

If the top CF stage gain is 18, then the 8k2 appears as as about 300k
which is apout 35Ra so the gain of the bottom gain stage is close to
µ. Some might use a j-fet CCS instead of the 8k2, and gain then is
even closer to tube µ but there isn't any advantage because with RL of
the gain tube anything over 250k the load line becomes near horizontal
and the distortion has reached close to a theoretical minimum.

Patrick Turner.



--
Regards,

John Byrns

Surf my web pages at, *http://fmamradios.com/

[Ian Iveson]

flipper wrote:

"Halved"? Doesn't the "mu-follower" still retain one of
the two "dc
load resistors" and its attendant "heat loss"? The plate
resistor for
the common cathode stage is not eliminated in the
"mu-follower" circuit,
it's simply bootstrapped to increase its impedance for the
AC signal.

It's even more fundamental than that. You have B+ and a
current That
power is dissipated regardless of what's in the circuit,
whether it's
a load resistor, triode plate, or anything else. Although,
if you do
it with a 'tube' you have the heater (or filament) to
power in
addition to the circuit itself.

So that's what fundamentalism is.

So if two stages pass, say, 3mA each, then twice as much
power is dissipated than in one stage passing 3mA, no matter
what's in the stages.

Equally, you could say that in the mu-follower, each valve
has half the HT voltage and the same current, hence half the
power dissipation.

Patrick's comment about the resistors is redundant, but his
point is good, although the assumption that the valves would
each be set up with the same current regardless of which
circuit was used may not be valid.

Ian

[Ian Iveson]

flipper wrote:

"Halved"? Doesn't the "mu-follower" still retain one of
the two "dc
load resistors" and its attendant "heat loss"? The
plate
resistor for
the common cathode stage is not eliminated in the
"mu-follower" circuit,
it's simply bootstrapped to increase its impedance for
the
AC signal.

It's even more fundamental than that. You have B+ and a
current That
power is dissipated regardless of what's in the circuit,
whether it's
a load resistor, triode plate, or anything else.
Although,
if you do
it with a 'tube' you have the heater (or filament) to
power in
addition to the circuit itself.

So that's what fundamentalism is.

Actually, yes.

I see, and an expert on actualness, to boot. What a
treasure.

So if two stages pass,

Who said anything about "two stages?"

But not too good at reading. There's more to it than knowing
words. Try to grasp how they fit together to make a meaning.
This is what Patrick wrote:

But the mu-follower is a nice simple linear gain circuit
with high Z
in, low Z out, and where the heat dissipation from a pair
of triodes
is halved because you have then in series without heat
loss in dc load
resistors.

Let me pick out the salient clause for you:

...the heat dissipation from a pair of triodes is halved
because you have them in series...

Now let's see how I worked out what he meant. He says two
valves, and says dissipation is halved when in series. That
suggests there is another way of connecting the two valves,
other than in series, where the dissipation is not halved.
With me so far?

Now can you think of another way of connecting the two
valves? Try completing the following sentence: "There are
two ways of connecting two things, either in series or in
....".

say, 3mA each, then twice as much
power is dissipated than in one stage passing 3mA, no
matter
what's in the stages.

Which is exactly what I said.

Well, I could choose to be childishly literal-minded and say
that it isn't quite, actually, what you said, but well done
anyway.

I'm trying to connect what I'm saying with what you said,
clearly, so you can see how what I'm saying fits in with the
context, which is what you and Patrick have said. I think
that's how conversations work. It's the dialectic. I
remember you said that's another thing you know everything
about, along with dielectrics and diatribe but sadly not
dialogue.

Equally, you could say that in the mu-follower, each valve
has half the HT voltage and the same current, hence half
the
power dissipation.

There are lots of things one could say but I was dealing
with what
people did say.

It's another way of saying the same thing. If you don't
understand, there's no point in me just repeating the same
as "what people did say". I felt that you had read the
words, but couldn't understand what they meant, put
together. So I tried to explain in a different way. Bit of
an uphill struggle though.

Patrick's comment about the resistors is redundant, but
his
point is good, although the assumption that the valves
would
each be set up with the same current regardless of which
circuit was used may not be valid.

I chose to not presume or imagine what Patrick 'meant',
which is why,
to his post, I asked "half power compared to what?"

See above. It is very obvious to me. Even John Burns could
see.

Ian

[Patrick Turner]

On Oct 12, 11:24*pm, "Ian Iveson"
wrote:
flipper wrote:
"Halved"? *Doesn't the "mu-follower" still retain one of
the two "dc
load resistors" and its attendant "heat loss"? *The plate
resistor for
the common cathode stage is not eliminated in the
"mu-follower" circuit,
it's simply bootstrapped to increase its impedance for the
AC signal.

It's even more fundamental than that. You have B+ and a
current That
power is dissipated regardless of what's in the circuit,
whether it's
a load resistor, triode plate, or anything else. Although,
if you do
it with a 'tube' you have the heater (or filament) to
power in
addition to the circuit itself.

So that's what fundamentalism is.

So if two stages pass, say, 3mA each, then twice as much
power is dissipated than in one stage passing 3mA, no matter
what's in the stages.

Equally, you could say that in the mu-follower, each valve
has half the HT voltage and the same current, hence half the
power dissipation.

Patrick's comment about the resistors is redundant, but his
point is good, although the assumption that the valves would
each be set up with the same current regardless of which
circuit was used may not be valid.

Ian- Hide quoted text -

- Show quoted text -

The mu-follower or SRPP as well allows the audio enthusiast to set up
his two series triodes with much more Ia flow than he would have with
a conventional common cathode gain stage with a resistance to deliver
the dc to the anode. This dc R load should be kept above 4Ra for
lowish THD which means about 39k for 1/2 a 6SN7. If you have B+ of
+300V then you can only have Ia = about 4mA or else Ea will be too low
for placement of the op point in the most linear region with a
resistance load.

Using two sections of 6SN7 ( or 6CG7 ) in series for mu-foll could
allow the same Ea = +300V for the bottom gain triode, say +140V, but
you could have Ia = 8 mA easily. The limiting factor would be the R
between bottom tube anode and top tube cathode because it eats voltage
swing headroom, but if you have a CCS instead of an R or even a choke
perhaps, you can ask the triodes to conduct maybe 10mA. With Ia rather
high the gm goes near its max and Ra to its lowest, and µ to the data
quoted values, and linearity is usually very good. Of course you can
dispense with the seriesed tube mu-follower arrangement and simply use
a CCS loaded triode direct coupled to a CF with a CCS cathode load.
Then the RL seen by the gain triode is a huge number of times Ra, so
gain virtually equals µ, or around 20 for 1/2 a 6SN7 and the
distortion will have fallen to its minimum value without reliance on
shunt NFB or current FB from an unbypassed Rk.

Wherever we use triodes with minumum signal Ia change they tend to
sound very well but one needs a follower to buffer such a stage from
the nature of loading effects we cannot always hence the need for a
follower of some sort. The followe can put up with the Ia change we
don't want in the gain stage because the series voltage NFB action of
the follower ensures low distortion.

Patrick Turner.

[Patrick Turner]

On Oct 13, 2:44*am, flipper wrote:
On Mon, 12 Oct 2009 13:24:44 +0100, "Ian Iveson"





wrote:
flipper wrote:

"Halved"? *Doesn't the "mu-follower" still retain one of
the two "dc
load resistors" and its attendant "heat loss"? *The plate
resistor for
the common cathode stage is not eliminated in the
"mu-follower" circuit,
it's simply bootstrapped to increase its impedance for the
AC signal.

It's even more fundamental than that. You have B+ and a
current That
power is dissipated regardless of what's in the circuit,
whether it's
a load resistor, triode plate, or anything else. Although,
if you do
it with a 'tube' you have the heater (or filament) to
power in
addition to the circuit itself.

So that's what fundamentalism is.

Actually, yes.



So if two stages pass,

Who said anything about "two stages?"

say, 3mA each, then twice as much
power is dissipated than in one stage passing 3mA, no matter
what's in the stages.

Which is exactly what I said.

Equally, you could say that in the mu-follower, each valve
has half the HT voltage and the same current, hence half the
power dissipation.

There are lots of things one could say but I was dealing with what
people did say.

Patrick's comment about the resistors is redundant, but his
point is good, although the assumption that the valves would
each be set up with the same current regardless of which
circuit was used may not be valid.

I chose to not presume or imagine what Patrick 'meant', which is why,
to his post, I asked "half power compared to what?"





Ian- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

Well then let me spell out what I did really mean.

Say you have TWO triodes, each 1/2 a 6SN7 or 6CG7.

One is arranged in a common cathode gain stage with R feeding DC to
anode.
It is direct coupled to a CF stage with Rk sinking dc to 0V.

Equal current flows in each triode, 3mA each.

So dc power consumed by the 2 stages is 0.003A x 300V x 2 = 1.8 Watts.

I ***compared** the two stage amp described above to a series arranged
mu-foll stage with the same B+ of +300V and the same Ia flowing in
each triode.
Regardless of what R connect the two triodes, dc power = 0.003A x 300V
x 1 = 0.9 Watts.

In a stereo preamp where all bells and whistles are present such as
dual pairs of outputs, tone control stages, line stages, phono amp
stages, AND where one wants high Z in and low Z out for all stages,
then the mu-follower stages will give better performance and use a
smaller power transformer than if one struggles to only use resistance
fed anodes or cathodes in conventional simple old fashioned circuitry.

For examples of what I mean, see my preamp pages at http://www.turneraudio.com.au

Patrick Turner.

[John Byrns]

In article ,
flipper wrote:

On Tue, 13 Oct 2009 02:53:28 -0700 (PDT), Patrick Turner
wrote:

On Oct 13, 2:44*am, flipper wrote:
On Mon, 12 Oct 2009 13:24:44 +0100, "Ian Iveson"





wrote:
flipper wrote:

"Halved"? *Doesn't the "mu-follower" still retain one of
the two "dc
load resistors" and its attendant "heat loss"? *The plate
resistor for
the common cathode stage is not eliminated in the
"mu-follower" circuit,
it's simply bootstrapped to increase its impedance for the
AC signal.

It's even more fundamental than that. You have B+ and a
current That
power is dissipated regardless of what's in the circuit,
whether it's
a load resistor, triode plate, or anything else. Although,
if you do
it with a 'tube' you have the heater (or filament) to
power in
addition to the circuit itself.

So that's what fundamentalism is.

Actually, yes.



So if two stages pass,

Who said anything about "two stages?"

say, 3mA each, then twice as much
power is dissipated than in one stage passing 3mA, no matter
what's in the stages.

Which is exactly what I said.

Equally, you could say that in the mu-follower, each valve
has half the HT voltage and the same current, hence half the
power dissipation.

There are lots of things one could say but I was dealing with what
people did say.

Patrick's comment about the resistors is redundant, but his
point is good, although the assumption that the valves would
each be set up with the same current regardless of which
circuit was used may not be valid.

I chose to not presume or imagine what Patrick 'meant', which is why,
to his post, I asked "half power compared to what?"





Ian- Hide quoted text -

- Show quoted text -- Hide quoted text -

- Show quoted text -

Well then let me spell out what I did really mean.

Say you have TWO triodes, each 1/2 a 6SN7 or 6CG7.

One is arranged in a common cathode gain stage with R feeding DC to
anode.
It is direct coupled to a CF stage with Rk sinking dc to 0V.

Equal current flows in each triode, 3mA each.

So dc power consumed by the 2 stages is 0.003A x 300V x 2 = 1.8 Watts.

I ***compared** the two stage amp described above to a series arranged
mu-foll stage with the same B+ of +300V and the same Ia flowing in
each triode.
Regardless of what R connect the two triodes, dc power = 0.003A x 300V
x 1 = 0.9 Watts.

In a stereo preamp where all bells and whistles are present such as
dual pairs of outputs, tone control stages, line stages, phono amp
stages, AND where one wants high Z in and low Z out for all stages,
then the mu-follower stages will give better performance and use a
smaller power transformer than if one struggles to only use resistance
fed anodes or cathodes in conventional simple old fashioned circuitry.

For examples of what I mean, see my preamp pages at
http://www.turneraudio.com.au

Patrick Turner.

Ah, I see. Yes, if one is doing a follower output anyway then it's
more power efficient to do a mu.

I would think that the most power efficient scheme would be to use
chokes to provide the power feed for both the gain and follower stages,
or a choke in place of the resistor in the "mu follower".

--
Regards,

John Byrns

Surf my web pages at, http://fmamradios.com/

[Ian Bell[_2_]]

John Byrns wrote:
In article ,
flipper wrote:

On Tue, 13 Oct 2009 02:53:28 -0700 (PDT), Patrick Turner
wrote:

On Oct 13, 2:44 am, flipper wrote:
On Mon, 12 Oct 2009 13:24:44 +0100, "Ian Iveson"





wrote:
flipper wrote:
"Halved"? Doesn't the "mu-follower" still retain one of
the two "dc
load resistors" and its attendant "heat loss"? The plate
resistor for
the common cathode stage is not eliminated in the
"mu-follower" circuit,
it's simply bootstrapped to increase its impedance for the
AC signal.
It's even more fundamental than that. You have B+ and a
current That
power is dissipated regardless of what's in the circuit,
whether it's
a load resistor, triode plate, or anything else. Although,
if you do
it with a 'tube' you have the heater (or filament) to
power in
addition to the circuit itself.
So that's what fundamentalism is.
Actually, yes.



So if two stages pass,
Who said anything about "two stages?"

say, 3mA each, then twice as much
power is dissipated than in one stage passing 3mA, no matter
what's in the stages.
Which is exactly what I said.

Equally, you could say that in the mu-follower, each valve
has half the HT voltage and the same current, hence half the
power dissipation.
There are lots of things one could say but I was dealing with what
people did say.

Patrick's comment about the resistors is redundant, but his
point is good, although the assumption that the valves would
each be set up with the same current regardless of which
circuit was used may not be valid.
I chose to not presume or imagine what Patrick 'meant', which is why,
to his post, I asked "half power compared to what?"





Ian- Hide quoted text -
- Show quoted text -- Hide quoted text -

- Show quoted text -
Well then let me spell out what I did really mean.

Say you have TWO triodes, each 1/2 a 6SN7 or 6CG7.

One is arranged in a common cathode gain stage with R feeding DC to
anode.
It is direct coupled to a CF stage with Rk sinking dc to 0V.

Equal current flows in each triode, 3mA each.

So dc power consumed by the 2 stages is 0.003A x 300V x 2 = 1.8 Watts.

I ***compared** the two stage amp described above to a series arranged
mu-foll stage with the same B+ of +300V and the same Ia flowing in
each triode.
Regardless of what R connect the two triodes, dc power = 0.003A x 300V
x 1 = 0.9 Watts.

In a stereo preamp where all bells and whistles are present such as
dual pairs of outputs, tone control stages, line stages, phono amp
stages, AND where one wants high Z in and low Z out for all stages,
then the mu-follower stages will give better performance and use a
smaller power transformer than if one struggles to only use resistance
fed anodes or cathodes in conventional simple old fashioned circuitry.

For examples of what I mean, see my preamp pages at
http://www.turneraudio.com.au

Patrick Turner.
Ah, I see. Yes, if one is doing a follower output anyway then it's
more power efficient to do a mu.

I would think that the most power efficient scheme would be to use
chokes to provide the power feed for both the gain and follower stages,
or a choke in place of the resistor in the "mu follower".



I think you are right about the inductor. ISTR Alan Kimmel did some
tests on one.

Cheers

IN

[Patrick Turner]

On Oct 14, 11:55*pm, John Byrns wrote:
In article ,





*flipper wrote:
On Tue, 13 Oct 2009 02:53:28 -0700 (PDT), Patrick Turner
wrote:

Snip a bit,,

For examples of what I mean, see my preamp pages at
http://www.turneraudio.com.au

Patrick Turner.

Ah, I see. Yes, if one is doing a follower output anyway then it's
more power efficient to do a mu.

I would think that the most power efficient scheme would be to use
chokes to provide the power feed for both the gain and follower stages,
or a choke in place of the resistor in the "mu follower".

Indeed chokes could be used for loading anodes and cathodes or between
triodes in a mu-foll.

Somewhat heavy and expensive though.

And the trouble with chokes is the iron caused distortion even at low
levels because a choke has a changeing impedance within a given
waveform, with a lower impedance around the zero crossing point of the
waves, and at all F.
And its worst when you have a fairly high source resistance driving
choke, and the 10k Ra of 1/2 a 6SN7 with say 4mA of Ia is not a low
enough source R to shunt the iron impedance. Iron inductance becomes
very low at very low signal levels especially those used in a preamp
and so although you might have L = 50H at say 40Vrms output, at
0.1Vrms the iron permability has dropped to a low level and so has the
inductance. I suggest my explanation is not fully informative and
probably unconvincing to those who like chokes in small signal amps. I
strongly suggest people try experimenting with a choke to see just how
much distortion they cause at low levels - and its more than the
distortion generated in the tubes.

( Having said that we could point a finger at OPTs in power amps. They
too generate HD. But in well designed OPT the iron caused HD is much
less than the tube HD, and its a low amount, and usually reduced by
the NFB loop around the amp, or shunted by low Ra triodes.....read
RDH4 for more details. The HD caused by the iron in tube amps is
rather like the crossover distortion in solid state amps, mainly 3H. )

But of course there are chokes and chokes, and an audio amateur will
just wind wire around whatever crummy second-hand olf iron he can
scrounge and that's probably going to make the most distortion no
matter how he gaps the iron and even if he uses 3 times the normal
number of turns.

Maybe if he were to use a gapped nickel E&I core or core of some other
material he might get a better behaving choke. But I've only used good
GOSS, and even that generates HD, 2H and 3H mostly, in a dc carrying
choke.

Finding suitable sizes of nickel or other material is like finding
rocking horse poo.

So I've never bothered with choke loading in preamps when the far
simpler, cheaper, and better performing solution is to use a
transistor CCS. OK, so maybe I waste a little power in the CCS, but
its a trifling amount.

I would guess the cost of purchgasing and installing chokes for
loadings in my preamps along with making a sturdier box to support the
weight might exceed the cost of the electricity I waste in the CCS
over the amps lifetime.

Efficiency can be measured over the longer term.

The anode efficiency of my tube preamp even with its 10 twin triodes
is of zero concern to me.
I use class A or AB power amps which "waste" far more power.

I am a modern person living in an energy rich democratic economy of
the early third millenium AD, and as such my lifestyle is dependant on
an external energy supply for my house and car which is about 0.5 KWH
for every hour I am alive.

I would be very happy if some government would arrange the energy
supplies to NOT be dependant on buring coal, oil, or gas or petroleum
products, so the sooner we all switch to nuclear, solar, wind power,
the better.

People will hate the costs of the huge changes involved when they find
out, which is why pollytishuns speak such utterly incomprehensible
bull**** with regard to climate change, and I won't hold my breath
waiting for things to change soon.
To find out more, read all the books written by James Lovelock. He
says we are about ****ed, and its too late to change, so survival will
be forced on us.

All with or without our tube amps as we see fit.

Patrick Turner.










--
Regards,

John Byrns

Surf my web pages at, *http://fmamradios.com/- Hide quoted text -

- Show quoted text -

[Christopher Paul]

Originally Posted by Ian Bell[_2_]

I have managed to contact Alan Kimmel who kindly passed on the info he
has about the origins of the mu-follower. He says:

"A mu stage and a mu follower are not exactly the same: "Mu follower" is
the name coined by Mr. Christopher Paul to describe a mu-mode stage that
has a triode tube on top.

"Mu stage" is the name for a mu-mode stage having a pentode or a MOSFET
on top. Having a high gain device on top such as a pentode or MOSFET
allows the "bottom" tube to attain 100% of its rated mu (or very close
to rated mu).

A few months after my Mu Stage article appeared in Glass Audio magazine,
Mr. Tim Fiddler of London, England contacted me and informed me that the
Mu Follower circuit idea had appeared as Fig. (b) on page 351 in
Electronic & Radio Engineer, Sept. 1958. On page 554 of Wireless
World, Nov. 1962, is a circuit similar to the Mu Stage. "

So, does anyone have either of these two magazines??

Cheers

Ian

Originally Posted by Christopher Paul:

A little history here. I presented a Mu Follower circuit in a letter in The Audio Amateur 2/85, p. 51 in which I discussed the circuit's properties of a gain and PSRR of about mu and a Zout near but larger than 1/gm. In a later letter to TAA in 3/91 on p. 43, I coined the phrase "Mu Follower" and provided a number equations describing its performace. Mr. Kimmel's Mu Stage appeared in Glass Audio in 1993, I believe.

Because of the similarities in topology and nickname, I suspect that the 'follower inspired the 'stage, but I'm not aware of Mr. Kimmel ever commenting on this.

The point is moot, however, because both circuits appear on the front cover of U.S. patent 2,631,197, filed in March of 1949 and granted in March 1953. The patent mentions the high gain and linearity and low Zout, but does not discuss PSRR. I'm indebted to John Broskie for finding this patent.

Regards, Chris