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NGS
 
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Default phase splitter

My guitar combo has five preamp tubes. They are all supposed to be
12AX7. For the effects send and return I use a 12AT7. For the first
preamp tube V1 I use a 5751. The last position V5 is the phase
splitter. What happens if I were to use a 5751 or 12AT7 or even 12AU7
in this position? Is it just the last boost stage prior to the power
tubes? Thanks.
  #2   Report Post  
Phil S
 
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"NGS" wrote in message
...
My guitar combo has five preamp tubes. They are all supposed to be
12AX7. For the effects send and return I use a 12AT7. For the first
preamp tube V1 I use a 5751. The last position V5 is the phase
splitter. What happens if I were to use a 5751 or 12AT7 or even 12AU7
in this position? Is it just the last boost stage prior to the power
tubes? Thanks.


In simple terms, the phase splitter of phase inverter (PI) divides the
signal so that half goes to each power tube in a push-pull design. (If
you've got 4 or 6 or 8 power tubes, there is a pair or group on each side
that acts as "one section".) I don't think it makes sense to use something
other than what's specified. For the other pre-amp tubes, use whatever
12A?7 tubes that give a sound you like. 7025 and 5751 are variants of the
12A?7 family. I think using another PI tube will give you signal loss at
the wrong place in the circuit.


  #3   Report Post  
NGS
 
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Phil S wrote:
"NGS" wrote in message
...

My guitar combo has five preamp tubes. They are all supposed to be
12AX7. For the effects send and return I use a 12AT7. For the first
preamp tube V1 I use a 5751. The last position V5 is the phase
splitter. What happens if I were to use a 5751 or 12AT7 or even 12AU7
in this position? Is it just the last boost stage prior to the power
tubes? Thanks.



In simple terms, the phase splitter of phase inverter (PI) divides the
signal so that half goes to each power tube in a push-pull design. (If
you've got 4 or 6 or 8 power tubes, there is a pair or group on each side
that acts as "one section".) I don't think it makes sense to use something
other than what's specified. For the other pre-amp tubes, use whatever
12A?7 tubes that give a sound you like. 7025 and 5751 are variants of the
12A?7 family. I think using another PI tube will give you signal loss at
the wrong place in the circuit.


Makes sense, thanks. Follow up question. Telefunken, Mullard, Amperex,
etc. obviously can be useful in "preamp" locations BUT for the phase
splitter does the TONAL QUALITY of the tube still matter. I'm guessing
it still does since it amplifies the signal going to the two power tubes
in PP but maybe not as much as say V1 or V2. Thanks.
  #4   Report Post  
Stephen Cowell
 
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Default


"NGS" wrote in message
...
My guitar combo has five preamp tubes. They are all supposed to be
12AX7. For the effects send and return I use a 12AT7. For the first
preamp tube V1 I use a 5751. The last position V5 is the phase
splitter. What happens if I were to use a 5751 or 12AT7 or even 12AU7
in this position? Is it just the last boost stage prior to the power
tubes? Thanks.


There's a little gain... it also provides both sides of the push-pull
final section with drive.

Marshalls use 12AX7 here... Fenders use 12AT7. Try both and
see what you like, can't hurt.
__
Steve
..


  #5   Report Post  
Phil S
 
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"NGS" wrote in message
...
Phil S wrote:
"NGS" wrote in message
...

My guitar combo has five preamp tubes. They are all supposed to be
12AX7. For the effects send and return I use a 12AT7. For the first
preamp tube V1 I use a 5751. The last position V5 is the phase
splitter. What happens if I were to use a 5751 or 12AT7 or even 12AU7
in this position? Is it just the last boost stage prior to the power
tubes? Thanks.



In simple terms, the phase splitter of phase inverter (PI) divides the
signal so that half goes to each power tube in a push-pull design. (If
you've got 4 or 6 or 8 power tubes, there is a pair or group on each

side
that acts as "one section".) I don't think it makes sense to use

something
other than what's specified. For the other pre-amp tubes, use whatever
12A?7 tubes that give a sound you like. 7025 and 5751 are variants of

the
12A?7 family. I think using another PI tube will give you signal loss

at
the wrong place in the circuit.


Makes sense, thanks. Follow up question. Telefunken, Mullard, Amperex,
etc. obviously can be useful in "preamp" locations BUT for the phase
splitter does the TONAL QUALITY of the tube still matter. I'm guessing
it still does since it amplifies the signal going to the two power tubes
in PP but maybe not as much as say V1 or V2. Thanks.


I've been told you can put a microphonic tube in this spot and generally it
won't be a problem. I'd put a decent tube in there, but wouldn't waste a
Tele or Mullard. The tone gets made before the PI.




  #6   Report Post  
WDB
 
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NGS wrote:
My guitar combo has five preamp tubes. They are all supposed to be
12AX7. For the effects send and return I use a 12AT7. For the first
preamp tube V1 I use a 5751. The last position V5 is the phase
splitter. What happens if I were to use a 5751 or 12AT7 or even 12AU7
in this position? Is it just the last boost stage prior to the power
tubes? Thanks.

Ok,
Here's the problem with using different tubes in the phase splitter spot.
A phase splitter or inverter has to not only supply the upper half
of the signal wave to one output tube and the lower half to the other
output tube, it also has to deliver sufficient voltage to cause the
output tubes to produce full power. For tubes like the EL34 and 6L6, we
are talking a phase inverter producing between 40 and 70 volts.
To get that kind of voltage swing out of a twin triode, you must use
the correct plate resistors and cathode resistors relative to the
impedance of the output tube's control grid circuit. Since the
specifications for cathode resistors relative to plate resistors and
next stage impedance are dramatically different when comparing a 12AX7
to a 12AT7 and 12AU7, using anything other then what the circuit was
designed for will net you less power from the amp. The 12AX7, 12AU7 and
12AT7 all have the same pin out connections, but that is where the
similarity ends. All three have different gain, different plate
impedance and different Gmu. To give an example. A 12AX7 in a standard
circuit has a plate impedance of around 60,000 ohms while a 12AU7 would
exhibit a plate impedance of around 7000 ohms. This also has an effect
on the frequency response of the amplifier and can net you loss of bass
or treble.
The 5751 is very similar to the 12Ax7. It is a kind of in between
tube between the 12AT7 and 12AX7. This tube will generally work anywhere
a 12AX7 will.
Hope this helps,
Bill B.
  #7   Report Post  
WDB
 
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I've been told you can put a microphonic tube in this spot and generally it
won't be a problem. I'd put a decent tube in there, but wouldn't waste a
Tele or Mullard. The tone gets made before the PI.


Not true unless your amp is strictly a preamp overdrive type with a
class AB2 or class B output stage. Every tube in the signal path has an
effect on sound quality. A poor quality tube used as the phase inverter
will cause the amp to lack life and punch. It is the number one reason I
have seen that Marshall and Fender amps sound weak. I have seen so many
people change out output tubes and preamp tubes thinking the phase
splitter tube is there just for the ride. It is the heart of a push pull
stage. In fact, a funky phase splitter circuit can cause your amp to
loose as much as 50% of it's power. Bad resistors, a bad tube and bad
coupling capacitors all contribute to phase splitter imbalance and the
result is a lousy sounding amp. I rebuild guitar and hifi amps for a
living and I don't know who started the 'urban legend' of putting your
junk tube in the phase splitter socket. If anything, this should be your
best tube. Also you should always use the correct tube in your phase
splitter socket. Do not try different types of tubes. If it calls for a
12AT7 use a 12AT7.
Bill B.
  #8   Report Post  
NGS
 
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Snip
The 5751 is very similar to the 12Ax7. It is a kind of in between
tube between the 12AT7 and 12AX7. This tube will generally work anywhere
a 12AX7 will.
Hope this helps,
Bill B.


It does, thank you and to all the responses.
  #9   Report Post  
Phil S
 
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"WDB" wrote in message
...

I've been told you can put a microphonic tube in this spot and generally

it
won't be a problem. I'd put a decent tube in there, but wouldn't waste

a
Tele or Mullard. The tone gets made before the PI.


Not true unless your amp is strictly a preamp overdrive type with a
class AB2 or class B output stage. Every tube in the signal path has an
effect on sound quality. A poor quality tube used as the phase inverter
will cause the amp to lack life and punch. It is the number one reason I
have seen that Marshall and Fender amps sound weak. I have seen so many
people change out output tubes and preamp tubes thinking the phase
splitter tube is there just for the ride. It is the heart of a push pull
stage. In fact, a funky phase splitter circuit can cause your amp to
loose as much as 50% of it's power. Bad resistors, a bad tube and bad
coupling capacitors all contribute to phase splitter imbalance and the
result is a lousy sounding amp. I rebuild guitar and hifi amps for a
living and I don't know who started the 'urban legend' of putting your
junk tube in the phase splitter socket. If anything, this should be your
best tube. Also you should always use the correct tube in your phase
splitter socket. Do not try different types of tubes. If it calls for a
12AT7 use a 12AT7.
Bill B.


Goes to show ya. Thanks for setting the record straight. Sorry for the
mis-info.


  #10   Report Post  
Dave Curtis
 
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Default

On Sat, 7 May 2005 23:05:10 -0400, "Phil S"
wrote:


"WDB" wrote in message
.. .

I've been told you can put a microphonic tube in this spot and generally

it
won't be a problem. I'd put a decent tube in there, but wouldn't waste

a
Tele or Mullard. The tone gets made before the PI.


Not true unless your amp is strictly a preamp overdrive type with a
class AB2 or class B output stage. Every tube in the signal path has an
effect on sound quality. A poor quality tube used as the phase inverter
will cause the amp to lack life and punch. It is the number one reason I
have seen that Marshall and Fender amps sound weak. I have seen so many
people change out output tubes and preamp tubes thinking the phase
splitter tube is there just for the ride. It is the heart of a push pull
stage. In fact, a funky phase splitter circuit can cause your amp to
loose as much as 50% of it's power. Bad resistors, a bad tube and bad
coupling capacitors all contribute to phase splitter imbalance and the
result is a lousy sounding amp. I rebuild guitar and hifi amps for a
living and I don't know who started the 'urban legend' of putting your
junk tube in the phase splitter socket. If anything, this should be your
best tube. Also you should always use the correct tube in your phase
splitter socket. Do not try different types of tubes. If it calls for a
12AT7 use a 12AT7.
Bill B.


Goes to show ya. Thanks for setting the record straight. Sorry for the
mis-info.


Not mis-info. You didn't say "junk tube", you said
decent. You're right about microphonics, too.
Normally not a problem in the PI hole.

IIRC, one of the regulars who used to post here
(Kent) put a 12AT7 in that spot to lower the drive
on his Marshall 4100, so whatever floats your
boat...

-Dave


  #11   Report Post  
Porky
 
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Along these lines, this Mann/Garnet bass amp I'm messing with at the
moment came with a 12AU7 PI tube. The tube is correct because the
sockets are labelled. This is a cathodyne-type PI where only one triode
is used, feeding one power tube with the plate and the other with the
cathode thru a resistor network. Similar to late 50's Tweed deluxe 5E3,
i think.

Anyways, what happens when I put in a 12AX7? The tone perks up, and the
amp is noticably louder. Obviously, the PI tube is providing more drive
to the output stage, and the amp has more punch. I will look at R
values and see if they need to be changed, butt...I'll be definitley
switching to the 12AX7.

Porky

  #12   Report Post  
Biskits n'Gravy
 
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"WDB" wrote in message
...

I've been told you can put a microphonic tube in this spot and generally

it
won't be a problem. I'd put a decent tube in there, but wouldn't waste

a
Tele or Mullard. The tone gets made before the PI.


Not true unless your amp is strictly a preamp overdrive type with a
class AB2 or class B output stage. Every tube in the signal path has an
effect on sound quality. A poor quality tube used as the phase inverter
will cause the amp to lack life and punch. It is the number one reason I
have seen that Marshall and Fender amps sound weak. I have seen so many
people change out output tubes and preamp tubes thinking the phase
splitter tube is there just for the ride. It is the heart of a push pull
stage. In fact, a funky phase splitter circuit can cause your amp to
loose as much as 50% of it's power. Bad resistors, a bad tube and bad
coupling capacitors all contribute to phase splitter imbalance and the
result is a lousy sounding amp. I rebuild guitar and hifi amps for a
living and I don't know who started the 'urban legend' of putting your
junk tube in the phase splitter socket. If anything, this should be your
best tube. Also you should always use the correct tube in your phase
splitter socket. Do not try different types of tubes. If it calls for a
12AT7 use a 12AT7.
Bill B.


I agree, and I tried replacing a Sovtek 12AX7 PI with an EH 12AT7 and it
didn't work well. Now I use a JJ ECC83 as the PI and it's great.


  #13   Report Post  
Chris Morriss
 
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Default

In message , Biskits
n'Gravy writes

"WDB" wrote in message
.. .

I've been told you can put a microphonic tube in this spot and generally

it
won't be a problem. I'd put a decent tube in there, but wouldn't waste

a
Tele or Mullard. The tone gets made before the PI.


Not true unless your amp is strictly a preamp overdrive type with a
class AB2 or class B output stage. Every tube in the signal path has an
effect on sound quality. A poor quality tube used as the phase inverter
will cause the amp to lack life and punch. It is the number one reason I
have seen that Marshall and Fender amps sound weak. I have seen so many
people change out output tubes and preamp tubes thinking the phase
splitter tube is there just for the ride. It is the heart of a push pull
stage. In fact, a funky phase splitter circuit can cause your amp to
loose as much as 50% of it's power. Bad resistors, a bad tube and bad
coupling capacitors all contribute to phase splitter imbalance and the
result is a lousy sounding amp. I rebuild guitar and hifi amps for a
living and I don't know who started the 'urban legend' of putting your
junk tube in the phase splitter socket. If anything, this should be your
best tube. Also you should always use the correct tube in your phase
splitter socket. Do not try different types of tubes. If it calls for a
12AT7 use a 12AT7.
Bill B.


I agree, and I tried replacing a Sovtek 12AX7 PI with an EH 12AT7 and it
didn't work well. Now I use a JJ ECC83 as the PI and it's great.


I'm amazed by how many people think that you can blindly swap around
12AT7, AU7 and AX7 in the search for a sound they like.

All these valves have totally different load and bias requirements, and
if you do get better sound when you swap in an AT7 instead of the
correct AX7, then there was something horribly wrong with the design in
the first place!
--
Chris Morriss
  #14   Report Post  
Paul D. Spiegel
 
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In rec.audio.tubes Chris Morriss wrote:
All these valves have totally different load and bias requirements, and
if you do get better sound when you swap in an AT7 instead of the
correct AX7, then there was something horribly wrong with the design in
the first place!


Chris, remember that these posters are discussing guitar amps, not
hi-fi. They may like the distortion products created by the wrong tube
performing at a non-linear operating point. It certainly isn't what the
circuit designer intended, but whether they like it or not is totally
subjective.

  #15   Report Post  
Ian Iveson
 
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"Paul D. Spiegel" wrote

Chris, remember that these posters are discussing guitar amps, not
hi-fi. They may like the distortion products created by the wrong
tube
performing at a non-linear operating point. It certainly isn't
what the
circuit designer intended, but whether they like it or not is
totally
subjective.


This is a popular but questionable view.

All musical instruments are easy to modify. You can put tin cans in
your piano, use a broken read for your saxophone, and put a dent in
your trumpet. Your new sound may excite for a while, but the novelty
soon fades and becomes irritating.

Clearly, orchestral instruments are standardised. Where the score
says "piano", it assumes a concert grand, not an upright stuffed
with tin cans. Some may argue that this is simply because the music
itself is externally specified, and so an orchestra is to some
extent like hi-fi: the aim is reproduction.

But there is more to it than that. Orchestral instruments were
developed over centuries. This refinement was opposed to
standardisation which therefore cannot explain it. Each instrument
was developed to have a sound that was *just right*, on its own and
in many combinations with others. This correctness was not just
subjective to the taste of its designer; it was and is a matter of
general, i.e. *social* perception. There is no such thing as private
music. It's a social movement with its own life that transcends the
individual artist, who can only contribute and develop, not invent.

Hence the iconic sounds of Hammond organ, Fender guitars, Marshall
and Fender amps. They produce the right basic palettes of sound,
with reasonable reliability.

A good guitar amp has a standard repertoire. Effects can be added,
but these are also generally standard.

Messing willy-nilly is unlikely to result in a musical sound.
Historic movements don't happen by chance. God doesn't play with
dice.

Designing an amp for mere reproduction is quite trivial. Producing
one that gets the performance *right* is much harder. This is true,
IMO, of both hi-fi and instruments.

So stick with the AU7 and play some proper music.

cheers, Ian




  #16   Report Post  
Patrick Turner
 
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Ian Iveson wrote:

"Paul D. Spiegel" wrote

Chris, remember that these posters are discussing guitar amps, not
hi-fi. They may like the distortion products created by the wrong
tube
performing at a non-linear operating point. It certainly isn't
what the
circuit designer intended, but whether they like it or not is
totally
subjective.


This is a popular but questionable view.

All musical instruments are easy to modify. You can put tin cans in
your piano, use a broken read for your saxophone, and put a dent in
your trumpet. Your new sound may excite for a while, but the novelty
soon fades and becomes irritating.

Clearly, orchestral instruments are standardised. Where the score
says "piano", it assumes a concert grand, not an upright stuffed
with tin cans. Some may argue that this is simply because the music
itself is externally specified, and so an orchestra is to some
extent like hi-fi: the aim is reproduction.

But there is more to it than that. Orchestral instruments were
developed over centuries. This refinement was opposed to
standardisation which therefore cannot explain it. Each instrument
was developed to have a sound that was *just right*, on its own and
in many combinations with others. This correctness was not just
subjective to the taste of its designer; it was and is a matter of
general, i.e. *social* perception. There is no such thing as private
music. It's a social movement with its own life that transcends the
individual artist, who can only contribute and develop, not invent.

Hence the iconic sounds of Hammond organ, Fender guitars, Marshall
and Fender amps. They produce the right basic palettes of sound,
with reasonable reliability.

A good guitar amp has a standard repertoire. Effects can be added,
but these are also generally standard.

Messing willy-nilly is unlikely to result in a musical sound.
Historic movements don't happen by chance. God doesn't play with
dice.

Designing an amp for mere reproduction is quite trivial. Producing
one that gets the performance *right* is much harder. This is true,
IMO, of both hi-fi and instruments.

So stick with the AU7 and play some proper music.

cheers, Ian


I hope your not in the same terse mood you had the other evening,
and I risk bringing up the subject of longtail pair
driver-phase splitters again.

The original poster says he has a guitar amp where
12AX7 is the specified tube for phase splitter.
We could assume its configured as an LTP,
and there is probably some NFB applied to one of the two inputs to the
LTP, since this is a common practice with LTP guitar amp drivers.

If 12AT7 or 12AU7 are just plugged in, they will sort of work,
but the amount of FB applied if any will be reduced, and the
balance of the drive voltages to each output tube will not be as close
as with 12AX7.
If anything, the sound at low level will be slightly warmer, since
there will be more 2H in the output signal, at least at low levels.

I doubt there is any harm in replacing 12AX7 with other tubes such as
12AT7, 12AU7,
12AY7, etc.
But the circuits of guitar amps do use different biasing and loadings so

that fairly optimal operation points are used for the driver LTP PI.
Subbing other tubes to get the same amount of correctness in working of
the subbed tube
means the loads and FB should be altered to suit.

The sound changes are anyone's guess, and I have difficulty co-relating
what musos say about the sound of their amps and the engineering.
But at least I can say a Vox AC30 with 4 x EL84 in pure class A
will sound warmer than a pair of 6L6 biased for near class B.


Fidelity is the enemy of the electric guitarist. All the musos I know
loathe a dry flat lifeless sound of an accurate amp, with SS amps
heading the list of loathability.
The heavy rock and rollers and heavy metals artistes like to
run with 40% IMD since the tubes are in heavy overdrive.
I would think that the choice of PI tube wouldn't make much difference.
I sure can't hear much difference, and it leaves me reaching for the
ear plugs when I ever am trapped into attending a "gig".
I don't like the ear damage effects of modern music venues.
The jazz guitarist, such as George Benson, relies on his amps to give
a kind of warm sound, well, that's ho I hear it from recordings
I have which I bought 20 years ago, and he's not into heavey clipping,
he exploits the musicality of the mildly distorted triodes
well before clipping starts.


Nearly all these dudes like to boost the hell out of the HF content of
the string information.
Without brightness, and presence, there is dullness, since the
jazz guitar and solid body electric guitar has truly dull sound when
played without an amp, since there is not the
more finely made wooden diaphragm to resonate that is a marvel
in a well made acoustic guitar used by say John Williams.

The pop and jazz players all like something that puts some magic into
what they are playing,
so that their musical talent, ( if they have any at all ) comes out
adorned with slightly or grossly tubaceous atifacts.
Reverb is somewhat important ihmo.

About all of what Ian has suggested about music and evolution of
instruments
is about right, and for hundreds of years the formal orchestra
instruments were inched
up to where they are now.
Then came electricity, and pickups, amplifiers, and eq-ing of the sound,

and effects, and musical expression has exploded to include genres
which would have been impossible in 1920.

Much of the "new music" is just noise by noisy boys, but
all ages precipitate the gems and throw out the trash.

Some of the black blues music from the 30s and 40s underpins
much of the modern pop music which is the majority of music
listened to today.
Some of those dudes get their music across best with simple note
playing,
simple picking styles, and there wasn't any real need to
have all the modern "featurisms" of the modern performance
to sing about how ****ed off one was about one's lerve life,
which was and remains is the predominating concern of people
young enough to try to clumsily relate to the opposite sex,
driven unmercifully by their primal urge to ****, attenuated by
vice and virtue ridden life decisions, fickle dispositions and consuming
emotions.

The electric guitar was able to cry their pains of hurt, desire, lust,
whatever, all by itself. Not to mention a saxophone.
If any music sums up western nation cultural expectations,
and the power of being with all our machines, its the electric guitar.


Of course the same personal relations subject matter was sung about in
1750
when guests in fine houses gathered to sing at the parties they held,
gathered around around the harsicord which was something jangly and
tinny,
and which appealed to youth of the day.

Steel strings would have been expensive for the poor in 1750, being the
product
of the industrial revolution.
So for centuries, gut strings dominated string instruments.

Later on the largely socially oppressed black in america could
at least afford 6 steel strings to moan the blues with some rythym,
and jazz got off the ground, all because of modern materials advances
and the invention of fast syncopation and rythym, a legacy out of
africa.

Last month I sat delighted while a woman played an electrified
concert harp. The complexity, and skill required to
play it is far greater than what most pop musicians could ever play.
The music she played was composed for the instrument, and
was used for some film soundtracks.
At times a bow was inserted between strings, to allow some
deep bass to be played along with what was running in the
"effects" box with many switchable effects used during the piece,
and always the music twisted and turned and wove us into its journey,
not boring us with repetition, or by peurile lack of ability.
There was zero reliance on tube amps to entertain us;
What entertained the audience of a thousand souls
was the training of the artiste, her discipline, and her natural
affinity
to make music, music composed to require and her abilty to let
music reach our souls without projection of her own
personal romantic disposition, devoid of the
pop musician's tiresome egotistical presense, which becomes a PITA
after a certain age afasiac.

Obviously, I am over 35, and have a mind, but at 20 I thought the Stones

were ok, and I liked Dylan, and the folk music that was around,
and the jazz, and the classical, except opera, which I thought
was pretentious.
The message often mattered most with the pop music and folk.
Butr when I listen now to the Stones on Beggar's Banquet I am bored,
embarrassed even, and I don't need to be reminded that
""I can't get no satisfaction"", and think now,
what's wrong with this jerk that he can't get no satisfaction?

All the Rap musos are wasting their time talking words of "music" to me,

and the lyrics simply have me thinking some serious growing
up has to be done, if they are ever to become honourable men,
and no amount of biasing of a 12AX7 phase inverter will ever pull these
kids out of the musical quagmire they are in.

Patrick Turner.


















  #17   Report Post  
 
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Patrick Turner wrote:

But at least I can say a Vox AC30 with 4 x EL84 in pure class A


groanWhose turn is it...?

  #18   Report Post  
Guncho
 
Posts: n/a
Default


Ian Iveson wrote:
"Paul D. Spiegel" wrote

Chris, remember that these posters are discussing guitar amps, not
hi-fi. They may like the distortion products created by the wrong
tube
performing at a non-linear operating point. It certainly isn't
what the
circuit designer intended, but whether they like it or not is
totally
subjective.


This is a popular but questionable view.

All musical instruments are easy to modify. You can put tin cans in
your piano, use a broken read for your saxophone, and put a dent in
your trumpet. Your new sound may excite for a while, but the novelty
soon fades and becomes irritating.

Clearly, orchestral instruments are standardised. Where the score
says "piano", it assumes a concert grand, not an upright stuffed
with tin cans. Some may argue that this is simply because the music
itself is externally specified, and so an orchestra is to some
extent like hi-fi: the aim is reproduction.

But there is more to it than that. Orchestral instruments were
developed over centuries. This refinement was opposed to
standardisation which therefore cannot explain it. Each instrument
was developed to have a sound that was *just right*, on its own and
in many combinations with others. This correctness was not just
subjective to the taste of its designer; it was and is a matter of
general, i.e. *social* perception. There is no such thing as private
music. It's a social movement with its own life that transcends the
individual artist, who can only contribute and develop, not invent.

Hence the iconic sounds of Hammond organ, Fender guitars, Marshall
and Fender amps. They produce the right basic palettes of sound,
with reasonable reliability.

A good guitar amp has a standard repertoire. Effects can be added,
but these are also generally standard.

Messing willy-nilly is unlikely to result in a musical sound.
Historic movements don't happen by chance. God doesn't play with
dice.

Designing an amp for mere reproduction is quite trivial. Producing
one that gets the performance *right* is much harder. This is true,
IMO, of both hi-fi and instruments.

So stick with the AU7 and play some proper music.

cheers, Ian


Yeah! And curse the Kinks for sticking pencils in their speakers to get
overdrive! If it it wasn't for them we would still be listening to jug
bands and old timey music like we should be!

Hyuck hyuck

Chris

  #19   Report Post  
Ian Iveson
 
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"Patrick Turner" wrote

...The original poster says he has a guitar amp where
12AX7 is the specified tube for phase splitter.
We could assume its configured as an LTP,
and there is probably some NFB applied to one of the two inputs to
the
LTP, since this is a common practice with LTP guitar amp
drivers...


It was the chap with the cathodyne that I had in mind. Yes most use
a long-tailed pair. It's not just about constant tone, but also
about the envelope, which at the extreme is shaped not just by the
front end, but also by the approach and onset of grid current in the
output stage, saturation of the OPT, sagging of the PS, the time it
takes and the manner in which it recovers from these things.

So you might expect a guitar amp cathodyne to include some building
out of the cathode load resistance, for example, so it deals with
grid current more gracefully and symmetrically. A bare concertina
can sound pretty bad if the cathode supplies current at the expense
of the anode.

Swap the AU7 or AT7 in such a critical circuit for an AX7 and I
would expect it to break up more suddenly, and less musically.

More generally, I suggest that blueprinting is more appropriate than
experimentation with any amplifier. Else you should at least decide
what change in sound you want *before* you modify.

...But at least I can say a Vox AC30 with 4 x EL84 in pure class A
will sound warmer than a pair of 6L6 biased for near class B...


Ah, the myth of the class A Vox. Check the load and the HT voltage.
Hot AB1, approaching AB2 I believe.

We're both pretty raw amateurs when it comes to guitar amps. Could
end up looking foolish on alt.guitar.amps. Eek!

cheers, Ian

PS opera can be ok live as long as it is not in English, which
invariably sounds daft. Recorded opera sounds daft anyway.


  #20   Report Post  
Ian Iveson
 
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"Guncho" wrote

Yeah! And curse the Kinks for sticking pencils in their speakers
to get
overdrive! If it it wasn't for them we would still be listening
to jug
bands and old timey music like we should be!


Of course! Now all guitar speakers come with pencils stuck in them,
we take them for granted.

I began by saying the popular "subjectivist" view was questionable,
not wrong. Actually it is quite true that "whether they like it or
not is totally subjective". What I question is whether it is
musical, which is the difficult and thorny issue.

If you fail to face that issue, then you end up with the untenable
view that *any* sound is music...that sound and music are identical,
and therefore music has no distinctive meaning.

The Kinks were part of a social movement and they were looking for a
particular sound. Messing about to no particular purpose is neither
of those things.

Of course there must be development, as I said. But progress is
social, and individuals can only grab the moment; ride the wave but
not create it. Certainly not by tinkering willy-nilly.

Hyuck hyuck


Sorry, I'm from RAT and I don't understand this bit.

cheers, Ian




  #22   Report Post  
Patrick Turner
 
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Ian Iveson wrote:

"Patrick Turner" wrote

...The original poster says he has a guitar amp where
12AX7 is the specified tube for phase splitter.
We could assume its configured as an LTP,
and there is probably some NFB applied to one of the two inputs to
the
LTP, since this is a common practice with LTP guitar amp
drivers...


It was the chap with the cathodyne that I had in mind. Yes most use
a long-tailed pair. It's not just about constant tone, but also
about the envelope, which at the extreme is shaped not just by the
front end, but also by the approach and onset of grid current in the
output stage, saturation of the OPT, sagging of the PS, the time it
takes and the manner in which it recovers from these things.

So you might expect a guitar amp cathodyne to include some building
out of the cathode load resistance, for example, so it deals with
grid current more gracefully and symmetrically. A bare concertina
can sound pretty bad if the cathode supplies current at the expense
of the anode.

Swap the AU7 or AT7 in such a critical circuit for an AX7 and I
would expect it to break up more suddenly, and less musically.

More generally, I suggest that blueprinting is more appropriate than
experimentation with any amplifier. Else you should at least decide
what change in sound you want *before* you modify.

...But at least I can say a Vox AC30 with 4 x EL84 in pure class A
will sound warmer than a pair of 6L6 biased for near class B...


Ah, the myth of the class A Vox. Check the load and the HT voltage.
Hot AB1, approaching AB2 I believe.


The couple of Vox AC30 I have repaired had over 12 watts dissipation in
each tube, and with the right load would clip gradually, like a
compressor.
EL34 and 6L6 tend not to do this.

The AC30 has cap coupling from whatever drive amp it has, and so cannot
sustain any grid current to give much more po than it already does,
which is about 30 watts, with about 20 being class A, which is a higher
% of class A than in most other guitar amps which are designed for
maximum loudness,
since musicians *really* want to be able to dominate once they are on
stage,
and who is going to hear them if they have a ****ant on an amp?
When most guitar amps are in gross over drive, the wave is a virtual
square wave with about 49% thd all mainly odd order, whether there
is any 2H present is utterly irrelevant.
But what guitar amps sound before they clip is of interest to those who
never over drive,
jazz musos etc.
The main harmonics in most guitar amps at low level is 3H, then 2H then
all the rest.

Its pot luck when what ever tubes are chosen that they sound musical.


We're both pretty raw amateurs when it comes to guitar amps. Could
end up looking foolish on alt.guitar.amps. Eek!


I repair a few guitar amps each year.
I dunno about you, but I am a professional



cheers, Ian

PS opera can be ok live as long as it is not in English, which
invariably sounds daft. Recorded opera sounds daft anyway.


I used to enjoy italian opera the best while painting a house.
Italian is a language begging to be sung, and since I don't understand a
word of it,
the story about ppl falling love, the jealousies, the murders, the
dramas that are all
largely implausible don't clutter my mind.

Even if I could speak italian, I'd not understand a word of opera,
as it is with operas in english, which may as well be german or french,
since opera mauls the diction and without subtitles I am stuffed.

So often when I see an opera performed and screened to the public via
the ABC TV network,
I can say I'd prefer a CD, since watching the pretentious acting and
mis-casting
with old folks in roles meant for the younger set is painful.
And folks pay $200 per ticket to go to the opera house.
There is an enormous pile of dross compared to the small
cup full of performances which are straight out gems that bring tears to
the eyes
when heard, even when you have zero idea of the drama plot.
Joan Sutherland in Acis and Galatea sung about 1962
is such a priceless item
I later saw her when she'd aged, and put a lotta weight on, and sang a
part in a role as a
pretty young thing and the object of desire amoungst the army officers
in their smart prussian uniforms.
I switched it off.

Nobody is going to poke garbage down my eyes, or ears.

Patrick Turner.


  #23   Report Post  
Ian Iveson
 
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PPS The post with the AU7 cathodyne is from Porky, who may no longer
be visible to some.

Porky, the extra drive is presumably because of the voltage
amplifier section of the AX7, not the section used for the
concertina, which has no gain itself no matter what valve you use.

If you need more gain, you may find it better to create it earlier
in the signal path.

cheers, Ian


  #24   Report Post  
Ant Moore
 
Posts: n/a
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Hi there,


"Patrick Turner" wrote in message
...


The AC30 has cap coupling from whatever drive amp it has, and so cannot

sustain any grid current to give much more po than it already does,
which is about 30 watts, with about 20 being class A, which is a higher
% of class A than in most other guitar amps which are designed for
maximum loudness,


So this makes the AC30 a hot class AB1.

Check out any schematic of the AC30. It specs 10-ishV on the
cathode resistor, rising to 12.5V at full output - implying increased
current consumption with increased output power. Sounds like class
AB to me, shifting slightly away from the class A region as the
output power increases.

Randall Aiken (www.aikenamps.com) has a good technical note
describing the AC30 output stage; well worth a look.

Cheers, and regards,


Ant. (Tamworth, UK)

--
"Make me one with everything." The Dalai Lama at a hot dog stand.


  #25   Report Post  
Ian Iveson
 
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"Jon Yaeger" wrote

Could you define "musical"?


No, is the short answer, if you are looking for analytical
precision.

Language, culture, art...similar ideas but all equally baffling. It
can be recognised though, and to some extent characterised.

Lots of social things and qualities defy definition or explanation.

In an interview with Bertrand Russell, G E Moore said, "Were anyone
to ask the meaning of good, I would say good is good, and let that
be the end of the matter." Got him an Oxford fellowship, so I guess
even clever people are flummoxed.

In the order of creation we are one level down from society. The
rest of the universe is spread below and relatively easy to grapple
with. Society is above and beyond the individual, and continues to
develop, but as individuals we don't. It gets more mysterious every
day, more apparently out of our control. As do the threads that bind
us, including music.

Sometimes we fight it only to discover that fighting is part of that
development.

The problem is quite clearly reflected in the core argument we have
on RAT, and on AGA by the look, as I read a few threads while I'm
here. Some say an amp is good if you like it, some say it has to be
right. The radical and the reactionary, iterated in virtually every
sphere of human social activity. The individual and the genre, if
you like.

I hope my children don't end up automatons. I have to side with the
radicals, but OTOH I know that to be effective it is necessary to
respect the equally inevitable truth of the reactionary.

The truth is staring us in the face but it's hard to see. Take the
following pair of equally true propositions:

A good amp is however you like it.
A good amp must be correct.

If you take that as a pair of simultaneous equations, or the first
two lines of a syllogism, a resolution is impossible because they
are mutually exclusive opposites. The challenge is to find a form of
logic that can produce a third resolving statement.

Music can discover resolution between opposites, it is good at that
kind of progression. Perhaps that is what it is for? Perhaps it is
the sound of society working on this very problem? Maybe we should
listen more carefully. Certainly we should all take part and learn
to play and sing...after all, we don't have many ways of grappling
with the Big Machine.

It's not that I am against modification, or individual sound,
whatever. It's just that idle messing, and interminable shallow
argument, don't do justice to the project.

Perhaps I should have stopped at "no".

cheers, Ian




  #26   Report Post  
 
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Ian Iveson wrote:

Ah, the myth of the class A Vox. Check the load and the HT voltage.
Hot AB1, approaching AB2 I believe.


So, you tell another myth in the opposite direction by implying that
such a ckt could possible operate AB2?

We're both pretty raw amateurs when it comes to guitar amps. Could
end up looking foolish on alt.guitar.amps. Eek!


That's innaccurate - by your statements, you indicate you are posers in
the whole area of basic tube technology...

  #27   Report Post  
Chris Hornbeck
 
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On Wed, 18 May 2005 17:27:45 GMT, "Ian Iveson"
wrote:

Perhaps I should have stopped at "no".


On the contrary. And I intend to quote this post into a
similar thread on r.a.p. The r.a.t provenance should
prove interesting, in context.

Much thanks,

Chris Hornbeck
"They're in *everybody's* eggs."
  #28   Report Post  
Ian Iveson
 
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wrote

Ah, the myth of the class A Vox. Check the load and the HT
voltage.
Hot AB1, approaching AB2 I believe.


So, you tell another myth in the opposite direction by implying
that
such a ckt could possible operate AB2?


Is there something you don't understand about "approaching"? What
opposite direction? More of a rotation I would say.

We're both pretty raw amateurs when it comes to guitar amps.
Could
end up looking foolish on alt.guitar.amps. Eek!


That's innaccurate - by your statements, you indicate you are
posers in
the whole area of basic tube technology...


Well I can't speak for Patrick, since he has now claimed to be a
"professional" wrt guitar amps. For myself, what do you think I am
posing as? An amateur? I can't quite grasp your problem here. I
didn't realise I was in AGA until these weirdos turned up.

cheers, Ian



  #29   Report Post  
claudel
 
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In article 8YQie.1821$6d.1@trnddc08, Hit by a Tree wrote:

On 17-May-2005, "Guncho" wrote:

Yeah! And curse the Kinks for sticking pencils in their speakers to get
overdrive!


Close. Dave Davies claims he slashed the cone with a razor blade.


Link Wray did the pencil thing in 1958 for "Rumble"...


Claude
  #31   Report Post  
Patrick Turner
 
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Hit by a Tree wrote:

On 18-May-2005, wrote:

Ah, the myth of the class A Vox. Check the load and the HT voltage.
Hot AB1, approaching AB2 I believe.


So, you tell another myth in the opposite direction by implying that
such a ckt could possible operate AB2?


Excerpt from:
http://www.guitaramplifiermagazine.c...m-classic6.htm

A Question of Class
A frequent topic of discussion amongst amp aficionados in bars, stores and
on bulletin boards the world over is this: Is the AC30 a class A amp? The
answer is, in a word, yes and noJ. “A lot of people call it class A because
it’s a cathode-biased class AB amp,” VOX’s chief designer, Steve Grindrod,
explains.


“If it was actually biased to full class A you’d be lucky to get
12 Watts out of it!


This is BS.
A pair of 6BQ5/EL84 biased at 13 watts like many are can have
pure class A efficiency of 45%, so expect 23 watts class A from a quad of tubes
working in class A and for the right load to get class A.
As soon as anyone uses a low load, say a 4 ohm speaker connected to the 8 ohm tap.
the amp starts working class AB.

Steve Grindford either doesn't know what he has designed,
or has been mis-quoted.

Don't take any notice of bar or cafe talk.
Go read RDH4 and learn the basics.



Plus it would generate an awful lot more heat than it
actually does. The AC30 acts as a Class A amp until the signal level hits a
certain point.


The samples I have seen run hot, ie, have at least 12 watts Pd at idle.

But it is actually a class AB1* amplifier which is the next
classification along from class A, so it has a lot of class A influence in
the way it compresses and delivers the sound. But, once you start to
overdrive the amp, that’s when you really can tell the difference between a
true class A amp and what an AC30 actually is...the AC30 is much more
efficient and also distorts more than a class A circuit.”


BS. with a huge overdrive it is impossible to tell any difference between
class B, AB, or A.
Square waves are being sent to the speaker, thd is 40%, imd = huge.

If an 8 ohms speaker is connected to the 16 ohm outlet,
the amp stays in class A, since the tubes do not cut off
until clipping and severe overdrive when all guitar amps
work in class C because the coupling caps are charged up
to over bias the tubes beyound class B.




A very important point! It should be pointed out that the AC30 Custom
Classic is no less Class A than all prior iterations of the AC30, from JMI
through today, and other so called Class A amplifiers, most of which have
cathode biased EL84 output valves.
*Note: Defining Class A operation as the bias being set so there is
continuous anode (plate) current in each output valve throughout the input
cycle (i.e. 360 degrees); class AB operation as the bias being adjusted so
that anode current flows for more than 50% (180 degrees) but less than 100%
(360 degrees) of the input cycle; and class B for no more than 50% of the
cycle. Where does class AB1 sit in all this? Well, class AB is subdivided
into AB1 and AB2 with class AB1 having a slightly higher bias than class A
with a larger input signal (having amplitudes reaching, but not exceeding,
the cutoff) and being defined as class AB operation where grid current
doesn’t flow for any portion of the input cycle.


In other words, depending on bias and RL, which you have not mentioned,
an AC30 will stay in class A for a large% of the power, and cross over into
class AB if RL is low.



IMPORTANT NOTE: As you will discover later, due to the Output Bias switch on
the rear panel of the Custom Classic it also operates as a class AB2 amp
when the “Warm” setting is chosen – this will be covered (and class AB2
defined) in the ‘Rear Panel Features’ section later on.


AB2?

The AC30 I have seen have cap coupling from the driver stage.

In overdrive ( above clipping ) the grid current in overdrive immediately
begins to alter the charge across the coupling caps
and the amp cannot be driven in into AB2 or A2 to any great
extent, and it isn't regarded as a class AB2 or A2 amp;
its just an over driven class AB1 amp which reverts to class C during big rifts.

For class A2 or AB2 you need to have direct coupled CF tubes to drive the output
grids,
and produce a substantial *linear* increase in power by forcing a big increase in
load V swing
by forcing the grid to go maybe 10v positive.

807 used to be used in AB2 with Ea = 600v, Eg2 = 300, CF grid drive,
and you'd get 80 watts AB2, at clipping.
In a guitar amp with huge overdrive, this would make smoke since
excess grid current would overload the grids, screens and anodes
with too much dissipation for too long.
But for clear speach such 80 watt amps were OK for PA.

So AB2 is rarely ever used in tube guitar amps; tubes would expire all too
frequently.

Patrick Turner.




--
Hit By a Tree!


  #32   Report Post  
Ian Iveson
 
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"Patrick Turner" whinged:

In other words, depending on bias and RL, which you have not
mentioned,
an AC30 will stay in class A for a large% of the power, and cross
over into
class AB if RL is low.
...cut rest of obfuscating BS


The specification of the AC30 includes its load, silly, and its bias
is not adjustable. An AC30 combo comes with its specified load
attached (inside, behind the cloth on the front). You are babbling
stupidly to cover up for your ignorant blurting, Mr Professional.

cheers, Ian


  #33   Report Post  
Porky
 
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I think it's Randy Davies, not Dave, slashed his speakers. Brother Ray
used a fork, and he stuck it in the back of his brother's hand, see
what that does to your sound, bro.

Porky.

  #34   Report Post  
Stephen Cowell
 
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"Ian Iveson" wrote in message
k...
"Patrick Turner" whinged:

In other words, depending on bias and RL, which you have not
mentioned,
an AC30 will stay in class A for a large% of the power, and cross
over into
class AB if RL is low.
...cut rest of obfuscating BS


The specification of the AC30 includes its load, silly, and its bias
is not adjustable. An AC30 combo comes with its specified load
attached (inside, behind the cloth on the front). You are babbling
stupidly to cover up for your ignorant blurting, Mr Professional.


Hey, this is pretty good! (Sound of corn popping in the bkgnd..)
Thanks for bringing it over here... keep slugging!
__
Steve
veteran of class A wars
..


  #35   Report Post  
Patrick Turner
 
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Ian Iveson wrote:

"Patrick Turner" whinged:

In other words, depending on bias and RL, which you have not
mentioned,
an AC30 will stay in class A for a large% of the power, and cross
over into
class AB if RL is low.
...cut rest of obfuscating BS


The specification of the AC30 includes its load, silly, and its bias
is not adjustable. An AC30 combo comes with its specified load
attached (inside, behind the cloth on the front). You are babbling
stupidly to cover up for your ignorant blurting, Mr Professional.


Well Mr Rank Amateur, you have not worked much on these things.
I assure you the AC30 has a lot more class A than nearly all other
guitar amps I have ever seen.
Its sound afaiac, is well liked by musos in the know.
Pentodes such as EL84 with a high bias current
and zero loop NFB overload like a nice gooey compressor.

And one can load the amp the way one wants to, but
the last one i had here for repairs due to blown tubes
etc **did** have very substantial class %.
The nominal speaker load is only that at one F, and either side rises
for bass resonance and for the voice coil inductance.

Patrick Turner.





cheers, Ian




  #36   Report Post  
Patrick Turner
 
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Porky wrote:

I think it's Randy Davies, not Dave, slashed his speakers. Brother Ray
used a fork, and he stuck it in the back of his brother's hand, see
what that does to your sound, bro.

Porky.


Mus be hard bonkin a groupie after a gig with a fork
holding a table to your arm.....

Patrick Turner.


  #37   Report Post  
Patrick Turner
 
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Stephen Cowell wrote:

"Ian Iveson" wrote in message
k...
"Patrick Turner" whinged:

In other words, depending on bias and RL, which you have not
mentioned,
an AC30 will stay in class A for a large% of the power, and cross
over into
class AB if RL is low.
...cut rest of obfuscating BS


The specification of the AC30 includes its load, silly, and its bias
is not adjustable. An AC30 combo comes with its specified load
attached (inside, behind the cloth on the front). You are babbling
stupidly to cover up for your ignorant blurting, Mr Professional.


Hey, this is pretty good! (Sound of corn popping in the bkgnd..)


Nah, that's the input 12AX7 that has just given up after 10 years.

Patrick Turner.


Thanks for bringing it over here... keep slugging!
__
Steve
veteran of class A wars
.


  #38   Report Post  
Ian Iveson
 
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"Patrick Turner" wrote

...snip babble...


And so, in a cloud of grey smoke, the graceless Patrick slithers
away.

Porky took not a blind bit of notice, BTW, and appears to have
fallen into the clutches of the half-baked hack calling himself
lbrty4us, who had the unmitigated audacity to suggest that you are a
poser "in the whole area of basic tube technology". If you nip over
to AGA you will find he writes such drivel that even you should be
able to give him a proper pounding, if you stick to RDH and don't
get carried away with more foolishness. Don't just paste him
willy-nilly though because he is right about some things.

Perhaps you could tell Porky about typical triode loading, and
direct him to datasheets where he can find typical operating
conditions and values for Ra and gm, so he can set up his daft AX7
cathodyne.

Just wondering if it's direct coupled, and if there is nfb to the
cathode of the preceding other half. Doesn't appear to know ohm's
law yet, could be right up your street.

cheers, Ian


  #39   Report Post  
 
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Ian Iveson wrote:

who had the unmitigated audacity to suggest that you are a
poser "in the whole area of basic tube technology".


Unfortunately, he's demonstrated this over a long period of confusing
or ignoring the basics.

If you nip over
to AGA you will find he writes such drivel that even you should be
able to give him a proper pounding, if you stick to RDH and don't
get carried away with more foolishness.


Had I noted - as I as I should have - that this all was x-posted
to/from audiophools, I would not have commited the error of annoying
and contending with the foolish and unteachable. Everytime he has
appeared on AGA he's made a complete ass of himself from any knowledge
& undersanding standpoint. It isn't clear, nor do I particularly care,
whether you may be in the same catagory.

Don't just paste him
willy-nilly though because he is right about some things.


While you are on the subject, I was clearly wrong in my misuse of the
word "topology", which in my disgust I mis-used to include component
values & operating point(s).

Perhaps you could tell Porky about typical triode loading, and
direct him to datasheets where he can find typical operating
conditions and values for Ra and gm, so he can set up his daft AX7
cathodyne.


This is just more typically mislead audiophool thinking; there is no
need to "set up his daft cathodyne" because he is a homebrewer simply
wishing to ape the practical performance of this simple, well-known,
70+yr-old ckt under one of its most common conditions of application &
use. Maybe you *are* as amiss & daft as PT, who knows. This is like
telling one to "set up" their Ford Model A when they are inquiring how
to change & inflate a tire.

Just wondering if it's direct coupled, and if there is nfb to the
cathode of the preceding other half. Doesn't appear to know ohm's
law yet, could be right up your street.


....and you guys should talk of not knowing basic laws, with all your
drivel...? Oy vey...

I will attempt to read headers better in the future.

  #40   Report Post  
NGS
 
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NGS wrote:
My guitar combo has five preamp tubes. They are all supposed to be
12AX7. For the effects send and return I use a 12AT7. For the first
preamp tube V1 I use a 5751. The last position V5 is the phase
splitter. What happens if I were to use a 5751 or 12AT7 or even 12AU7
in this position? Is it just the last boost stage prior to the power
tubes? Thanks.


Very interesting responses, very educational and some very entertaining.

ANYWAY. I'm going ahead with all 5751 in all positions now including
the efx send and return except the last gain stage V3 where I'm going to
use a Mullard 12AT7 to soften up the boogie a bit.
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