[PenttiL[_2_]]

Just ask. If there's an amp output push-pull stage planned to work four
EL 84 or two EL 34 and the class is the same, what are the differences
I can clearly hear depend the different character between the tubes?

I think the differences between the guitar amps Vox AC 30 ( EL 84 ) and
some Marshall combos ( build EL 34 ) depend from that the Vox has build
to class A ( more clear sound ) and Marshall class AB or B ( more
powerful sound at solos, but chords sounds always a little "muddy".
Also theres some differences on the character of distortion you can hear
when you play more loud volumes depend the different tubes...?

-Pentti

[PenttiL[_2_]]

PenttiL wrote:
Just ask. If there's an amp output push-pull stage planned to work four
EL 84 or two EL 34 and the class is the same, what are the differences
I can clearly hear depend the different character between the tubes?

I think the differences between the guitar amps Vox AC 30 ( EL 84 ) and
some Marshall combos ( build EL 34 ) depend from that the Vox has build
to class A ( more clear sound ) and Marshall class AB or B ( more
powerful sound at solos, but chords sounds always a little "muddy".
Also theres some differences on the character of distortion you can hear
when you play more loud volumes depend the different tubes...?

-Pentti

Funny how, maybe no one will have some experiences with these valve
types I asked. At least, EL 84 will expanse some presence frequencies
and EL 34 will make some more power on low end. Is this true?

-Pentti

[mick]

On Fri, 17 Oct 2008 15:40:50 +0300, PenttiL wrote:

PenttiL wrote:
Just ask. If there's an amp output push-pull stage planned to work four
EL 84 or two EL 34 and the class is the same, what are the differences
I can clearly hear depend the different character between the tubes?

I think the differences between the guitar amps Vox AC 30 ( EL 84 ) and
some Marshall combos ( build EL 34 ) depend from that the Vox has build
to class A ( more clear sound ) and Marshall class AB or B ( more
powerful sound at solos, but chords sounds always a little "muddy".
Also theres some differences on the character of distortion you can
hear when you play more loud volumes depend the different tubes...?

-Pentti

Funny how, maybe no one will have some experiences with these valve
types I asked. At least, EL 84 will expanse some presence frequencies
and EL 34 will make some more power on low end. Is this true?



Don't concentrate too much on the valve types. Both of those are similar
in many ways (the EL34 is the "big brother" of the EL84). Changes in the
circuit, including the OPT characteristics, the output stage biasing and
the capabilities of the driver stage will make such huge differences that
it's rather silly to make comparisons - at least of correctly designed
amps.

Guitar amps in particular are such a personal choice that all comparisons
become meaningless.

Some people claim that the EL84 sounds better in hi-fi applications, even
if it is under-powered. OTOH the EL34 is a workhorse valve, designed for
high output, and is probably better where power is considered to be more
important than sound quality. I'm not going to give an opinion either way!

It's no surprise really that you aren't getting many replies. ;-)

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info http://mixpix.batcave.net
Filtering everything posted from googlegroups to kill spam.

[Dominique Michel[_2_]]

Le Fri, 17 Oct 2008 18:16:27 GMT,
mick a écrit :

On Fri, 17 Oct 2008 15:40:50 +0300, PenttiL wrote:

PenttiL wrote:
Just ask. If there's an amp output push-pull stage planned to work four
EL 84 or two EL 34 and the class is the same, what are the differences
I can clearly hear depend the different character between the tubes?

I think the differences between the guitar amps Vox AC 30 ( EL 84 ) and
some Marshall combos ( build EL 34 ) depend from that the Vox has build
to class A ( more clear sound ) and Marshall class AB or B ( more
powerful sound at solos, but chords sounds always a little "muddy".
Also theres some differences on the character of distortion you can
hear when you play more loud volumes depend the different tubes...?

-Pentti

Funny how, maybe no one will have some experiences with these valve
types I asked. At least, EL 84 will expanse some presence frequencies
and EL 34 will make some more power on low end. Is this true?



Don't concentrate too much on the valve types. Both of those are similar
in many ways (the EL34 is the "big brother" of the EL84). Changes in the
circuit, including the OPT characteristics, the output stage biasing and
the capabilities of the driver stage will make such huge differences that
it's rather silly to make comparisons - at least of correctly designed
amps.

Guitar amps in particular are such a personal choice that all comparisons
become meaningless.

Some people claim that the EL84 sounds better in hi-fi applications, even
if it is under-powered. OTOH the EL34 is a workhorse valve, designed for
high output, and is probably better where power is considered to be more
important than sound quality. I'm not going to give an opinion either way!


The bad sound quality of most high power all valves guitar amps doesn't come
from the valve types but from the driver stage that cannot drive the needed
power for the command grid of a class B output stage at full volume driven by a
guitar.

The signal from a guitar is not a sinus at all but have a very big pulse of
harmonics at the beginning of each period (especially with single humbugging
microphones). That implies that the command grid of a class B push pull will
become positive at high output during those pulses. I don't know any commercial
high power all valves guitar amp where the driver is able to deliver the 2 or 3
watts (for a 6L6 or EL34 push-pull) needed by the command grids of the output
stage during those pulses.

To deliver that power will implies that the main supply will be able to
drive the output stage and that the output stage must be carefully
designed in order to handle this (the g2 can get very hot). This is possible to
archive, but not at the cost of a commercial guitar amp. And even if you made
your own such designed amp, the cost will be high.

You can even stabilize the G2 of the output stage of a class B guitar amp. You
will get an outstanding dynamic, and that even at full power, but this have a
cost and it will be very easy to blow the tubes and the transformer if the
circuit of all the parts is not very carefully designed.

As example, the most expansive marshall don't cost more as 100$ to manufacture.
If it was not the case, they would made something else.

Ciao,
Dominique

It's no surprise really that you aren't getting many replies. ;-)



--
Dominique Michel

Mes 3 projets préférés auxquels je contribue:
* FVWM-Crystal, le bureau basé sur FVWM:
http://fvwm-crystal.org
* AlsaPlayer, le lecteur audio avec contrôle de vitesse en continu:
www.alsaplayer.org
* L'overlay pour la MAO sous gentoo:
http://proaudio.tuxfamily.org/wiki/i...itle=Main_Page

[jh]

Dominique Michel schrieb:
Le Fri, 17 Oct 2008 18:16:27 GMT,
mick a écrit :

On Fri, 17 Oct 2008 15:40:50 +0300, PenttiL wrote:

PenttiL wrote:
Just ask. If there's an amp output push-pull stage planned to work four
EL 84 or two EL 34 and the class is the same, what are the differences
I can clearly hear depend the different character between the tubes?

I think the differences between the guitar amps Vox AC 30 ( EL 84 ) and
some Marshall combos ( build EL 34 ) depend from that the Vox has build
to class A ( more clear sound ) and Marshall class AB or B ( more
powerful sound at solos, but chords sounds always a little "muddy".
Also theres some differences on the character of distortion you can
hear when you play more loud volumes depend the different tubes...?

-Pentti
Funny how, maybe no one will have some experiences with these valve
types I asked. At least, EL 84 will expanse some presence frequencies
and EL 34 will make some more power on low end. Is this true?


Don't concentrate too much on the valve types. Both of those are similar
in many ways (the EL34 is the "big brother" of the EL84). Changes in the
circuit, including the OPT characteristics, the output stage biasing and
the capabilities of the driver stage will make such huge differences that
it's rather silly to make comparisons - at least of correctly designed
amps.

Guitar amps in particular are such a personal choice that all comparisons
become meaningless.

Some people claim that the EL84 sounds better in hi-fi applications, even
if it is under-powered. OTOH the EL34 is a workhorse valve, designed for
high output, and is probably better where power is considered to be more
important than sound quality. I'm not going to give an opinion either way!


The bad sound quality of most high power all valves guitar amps doesn't come
from the valve types but from the driver stage that cannot drive the needed
power for the command grid of a class B output stage at full volume driven by a
guitar.

The signal from a guitar is not a sinus at all but have a very big pulse of
harmonics at the beginning of each period (especially with single humbugging
microphones). That implies that the command grid of a class B push pull will
become positive at high output during those pulses. I don't know any commercial
high power all valves guitar amp where the driver is able to deliver the 2 or 3
watts (for a 6L6 or EL34 push-pull) needed by the command grids of the output
stage during those pulses.

To deliver that power will implies that the main supply will be able to
drive the output stage and that the output stage must be carefully
designed in order to handle this (the g2 can get very hot). This is possible to
archive, but not at the cost of a commercial guitar amp. And even if you made
your own such designed amp, the cost will be high.

You can even stabilize the G2 of the output stage of a class B guitar amp. You
will get an outstanding dynamic, and that even at full power, but this have a
cost and it will be very easy to blow the tubes and the transformer if the
circuit of all the parts is not very carefully designed.

As example, the most expansive marshall don't cost more as 100$ to manufacture.
If it was not the case, they would made something else.

Ciao,
Dominique

It's no surprise really that you aren't getting many replies. ;-)




... dear dominique

might it be that the imperfections you cite *are* the reason, why so
many guitar players and musos swear on exactly those amps?

realistic sound reproduction and "perfect" ampifiers ain't what guitar
players like. Do yourself a favour an listen to one of those imperfect
amp (e.g. Fender 5E3 tweed deluxe or a 1987 50W Marshall) in the hands
of a really good musician. Give him a "real good" amp - hifi wise _ and
listen again......


just my 2cts

regards

Jochen

[Dominique Michel[_2_]]

Le Mon, 20 Oct 2008 23:49:12 +0200,
jh a écrit :

Dominique Michel schrieb:
Le Fri, 17 Oct 2008 18:16:27 GMT,
mick a écrit :

On Fri, 17 Oct 2008 15:40:50 +0300, PenttiL wrote:

PenttiL wrote:
Just ask. If there's an amp output push-pull stage planned to work four
EL 84 or two EL 34 and the class is the same, what are the differences
I can clearly hear depend the different character between the tubes?

I think the differences between the guitar amps Vox AC 30 ( EL 84 ) and
some Marshall combos ( build EL 34 ) depend from that the Vox has build
to class A ( more clear sound ) and Marshall class AB or B ( more
powerful sound at solos, but chords sounds always a little "muddy".
Also theres some differences on the character of distortion you can
hear when you play more loud volumes depend the different tubes...?

-Pentti
Funny how, maybe no one will have some experiences with these valve
types I asked. At least, EL 84 will expanse some presence frequencies
and EL 34 will make some more power on low end. Is this true?


Don't concentrate too much on the valve types. Both of those are similar
in many ways (the EL34 is the "big brother" of the EL84). Changes in the
circuit, including the OPT characteristics, the output stage biasing and
the capabilities of the driver stage will make such huge differences that
it's rather silly to make comparisons - at least of correctly designed
amps.

Guitar amps in particular are such a personal choice that all comparisons
become meaningless.

Some people claim that the EL84 sounds better in hi-fi applications, even
if it is under-powered. OTOH the EL34 is a workhorse valve, designed for
high output, and is probably better where power is considered to be more
important than sound quality. I'm not going to give an opinion either way!


The bad sound quality of most high power all valves guitar amps doesn't come
from the valve types but from the driver stage that cannot drive the needed
power for the command grid of a class B output stage at full volume driven
by a guitar.

The signal from a guitar is not a sinus at all but have a very big pulse of
harmonics at the beginning of each period (especially with single humbugging
microphones). That implies that the command grid of a class B push pull will
become positive at high output during those pulses. I don't know any
commercial high power all valves guitar amp where the driver is able to
deliver the 2 or 3 watts (for a 6L6 or EL34 push-pull) needed by the
command grids of the output stage during those pulses.

To deliver that power will implies that the main supply will be able to
drive the output stage and that the output stage must be carefully
designed in order to handle this (the g2 can get very hot). This is
possible to archive, but not at the cost of a commercial guitar amp. And
even if you made your own such designed amp, the cost will be high.

You can even stabilize the G2 of the output stage of a class B guitar amp.
You will get an outstanding dynamic, and that even at full power, but this
have a cost and it will be very easy to blow the tubes and the transformer
if the circuit of all the parts is not very carefully designed.

As example, the most expansive marshall don't cost more as 100$ to
manufacture. If it was not the case, they would made something else.

Ciao,
Dominique

It's no surprise really that you aren't getting many replies. ;-)




.. dear dominique

might it be that the imperfections you cite *are* the reason, why so
many guitar players and musos swear on exactly those amps?

realistic sound reproduction and "perfect" ampifiers ain't what guitar
players like. Do yourself a favour an listen to one of those imperfect
amp (e.g. Fender 5E3 tweed deluxe or a 1987 50W Marshall) in the hands
of a really good musician. Give him a "real good" amp - hifi wise _ and
listen again......


Already done. Both are great commercial amps, but nothing more for me.Take a
look at the 5E2 schema. The driver have a high impedance output. That imply
that it cannot drive the grids of the output stage when they are in saturation.
Power tubes need power onto the grid in order to get a good dynamic when this
grid is into saturation.


just my 2cts

regards

Jochen

You cannot compare a guitar amp with an hifi amp. A guitar amp is some kind of
power operational amplifier in open loop. (Even if the internal design is
completely different, they share many things like the gain, the ability to
fully saturate, and the limited bandwitch.) A few milivolts at the entry can
give you full output, it is a very huge gain, it have no feedback and you can
get saturation in all the stages. So, you just cannot compare it with an hifi
device.

I am just talking here about a class B guitar amp with an outstanding dynamic
at full output, something that will drive the speaker into one controlled jet
reactor when playing at high volume. That will give you the best of both
sounds : a powerful saturation but with all the flavors of a great clear
sound at the same time.

I was not even talking about the bandwitch of such amplifiers. Why do you think
that most guitar players in the world do have the treble knob almost at the
maximum gain, the middle know at a very low setting and the bass at a
relatively high setting? Only because their amps and their loudspeakers are just
good medium devices.

But it is normal. An operational amp in open loop like a guitar amp cannot have
a regular bandwitch between 20Hz to 20kHz. You will have to introduce some kind
of feedback for that, and feedback is definitely not what I like into a guitar
amp.

For the bandwitch, it is not many things you can do into the preamp. Triode in
class A without feedback do have limited bandwitch. The type of tube will give
you some latitude : higher mu implies more facility to saturate but less
bandwitch.

But for the driver, you can use something like a class A EL84 in triode with
transformer coupling to the output. A very good quality transformer can give you
an outstanding bandwitch, but it will cost a lot of money and you will not find
such a circuit into a commercial guitar amp. Such a transformer will be a little
bigger that the output transformer of a fender champ, but it will be able to
drive the grids of 2 power tubes like EL34 when they are into saturation.

Cheers,
Dominique
--
Dominique Michel

Mes 3 projets préférés auxquels je contribue:
* FVWM-Crystal, le bureau basé sur FVWM:
http://fvwm-crystal.org
* AlsaPlayer, le lecteur audio avec contrôle de vitesse en continu:
www.alsaplayer.org
* L'overlay pour la MAO sous gentoo:
http://proaudio.tuxfamily.org/wiki/i...itle=Main_Page

[jh]

Dominique Michel schrieb:
Le Mon, 20 Oct 2008 23:49:12 +0200,
jh a écrit :

Dominique Michel schrieb:
Le Fri, 17 Oct 2008 18:16:27 GMT,
mick a écrit :

On Fri, 17 Oct 2008 15:40:50 +0300, PenttiL wrote:

PenttiL wrote:
Just ask. If there's an amp output push-pull stage planned to work four
EL 84 or two EL 34 and the class is the same, what are the differences
I can clearly hear depend the different character between the tubes?

I think the differences between the guitar amps Vox AC 30 ( EL 84 ) and
some Marshall combos ( build EL 34 ) depend from that the Vox has build
to class A ( more clear sound ) and Marshall class AB or B ( more
powerful sound at solos, but chords sounds always a little "muddy".
Also theres some differences on the character of distortion you can
hear when you play more loud volumes depend the different tubes...?

-Pentti
Funny how, maybe no one will have some experiences with these valve
types I asked. At least, EL 84 will expanse some presence frequencies
and EL 34 will make some more power on low end. Is this true?

Don't concentrate too much on the valve types. Both of those are similar
in many ways (the EL34 is the "big brother" of the EL84). Changes in the
circuit, including the OPT characteristics, the output stage biasing and
the capabilities of the driver stage will make such huge differences that
it's rather silly to make comparisons - at least of correctly designed
amps.

Guitar amps in particular are such a personal choice that all comparisons
become meaningless.

Some people claim that the EL84 sounds better in hi-fi applications, even
if it is under-powered. OTOH the EL34 is a workhorse valve, designed for
high output, and is probably better where power is considered to be more
important than sound quality. I'm not going to give an opinion either way!

The bad sound quality of most high power all valves guitar amps doesn't come
from the valve types but from the driver stage that cannot drive the needed
power for the command grid of a class B output stage at full volume driven
by a guitar.

The signal from a guitar is not a sinus at all but have a very big pulse of
harmonics at the beginning of each period (especially with single humbugging
microphones). That implies that the command grid of a class B push pull will
become positive at high output during those pulses. I don't know any
commercial high power all valves guitar amp where the driver is able to
deliver the 2 or 3 watts (for a 6L6 or EL34 push-pull) needed by the
command grids of the output stage during those pulses.

To deliver that power will implies that the main supply will be able to
drive the output stage and that the output stage must be carefully
designed in order to handle this (the g2 can get very hot). This is
possible to archive, but not at the cost of a commercial guitar amp. And
even if you made your own such designed amp, the cost will be high.

You can even stabilize the G2 of the output stage of a class B guitar amp.
You will get an outstanding dynamic, and that even at full power, but this
have a cost and it will be very easy to blow the tubes and the transformer
if the circuit of all the parts is not very carefully designed.

As example, the most expansive marshall don't cost more as 100$ to
manufacture. If it was not the case, they would made something else.

Ciao,
Dominique

It's no surprise really that you aren't getting many replies. ;-)


.. dear dominique

might it be that the imperfections you cite *are* the reason, why so
many guitar players and musos swear on exactly those amps?

realistic sound reproduction and "perfect" ampifiers ain't what guitar
players like. Do yourself a favour an listen to one of those imperfect
amp (e.g. Fender 5E3 tweed deluxe or a 1987 50W Marshall) in the hands
of a really good musician. Give him a "real good" amp - hifi wise _ and
listen again......


Already done. Both are great commercial amps, but nothing more for me.Take a
look at the 5E2 schema. The driver have a high impedance output. That imply
that it cannot drive the grids of the output stage when they are in saturation.
Power tubes need power onto the grid in order to get a good dynamic when this
grid is into saturation.


the sound is pristine, but obviously not your piece of cake. I love my
5E3 and the guys at the local jam who also play it regularly do that
too... Of course this amp does not have 20k, it's more 12k or 15k, but
the speaker limits it to about 5k-6k anyway....

just my 2cts

regards

Jochen

You cannot compare a guitar amp with an hifi amp. A guitar amp is some kind of
power operational amplifier in open loop. (Even if the internal design is
completely different, they share many things like the gain, the ability to
fully saturate, and the limited bandwitch.) A few milivolts at the entry can
give you full output, it is a very huge gain, it have no feedback and you can
get saturation in all the stages. So, you just cannot compare it with an hifi
device.


Why? Compare the power amps of a tube hifi and a guit amp. Not that
different at all.


I am just talking here about a class B guitar amp with an outstanding dynamic
at full output, something that will drive the speaker into one controlled jet
reactor when playing at high volume. That will give you the best of both
sounds : a powerful saturation but with all the flavors of a great clear
sound at the same time.

? the natural compression is e.g. exactly what *I* like. Obviously
there's a lot of cakes on this planet and different tastes. The
assymetrical clip of a 5E3 PI gives you a lot of possibilities too.
Imperfection in perfection.


I was not even talking about the bandwitch of such amplifiers. Why do you think
that most guitar players in the world do have the treble knob almost at the
maximum gain, the middle know at a very low setting and the bass at a
relatively high setting? Only because their amps and their loudspeakers are just
good medium devices.


different styles. Not all of them do that. You won't play completly
scooped mids with a 70s 50W Marshall.... The classic and beloved first
early 60s Voxes did not even have a real treble knob.

the scoopers want the edge and aggression in the 4-8k region and a real
thump in the lower registers. Imho 10k-15k with overdrive sounds like
a wasp in the card box. But the speakers limit the higher freqs anyway...
The local feedback at the presence does it part too, by increasing the
distortion patterns ath higher freqs.


But it is normal. An operational amp in open loop like a guitar amp cannot have
a regular bandwitch between 20Hz to 20kHz. You will have to introduce some kind
of feedback for that, and feedback is definitely not what I like into a guitar
amp.


You have obviously not measured the real bandwidth of a guitar amp yet.


For the bandwitch, it is not many things you can do into the preamp. Triode in
class A without feedback do have limited bandwitch.

Not necessarily. A triode without feedback can easily go up to 60K

The type of tube will give
you some latitude : higher mu implies more facility to saturate but less
bandwitch.


Why saturate the preamp when you've got a power amp?

But for the driver, you can use something like a class A EL84 in triode with
transformer coupling to the output. A very good quality transformer can give you
an outstanding bandwitch, but it will cost a lot of money and you will not find
such a circuit into a commercial guitar amp.


I have one on the bench at the moment...In this one the interstage
transformer is bigger than the OT of a champ. More like that of a super
reverb. Although it's one of the best amps I've ever heard and played
(clean) the buzz is not that grat, if driven.

Such a transformer will be a little
bigger that the output transformer of a fender champ, but it will be able to
drive the grids of 2 power tubes like EL34 when they are into saturation.


If you really insist do do that, put a 12AU7 CF in front of the grids
and you are there too.....

Dominique,

Saying that "that is the reason, why Marshalls sound so bad" is
nonsense...There's simply different tastes.

regards
Jochen


Cheers,
Dominique

[Eeyore]

PenttiL wrote:

PenttiL wrote:
Just ask. If there's an amp output push-pull stage planned to work four
EL 84 or two EL 34 and the class is the same, what are the differences
I can clearly hear depend the different character between the tubes?

I think the differences between the guitar amps Vox AC 30 ( EL 84 ) and
some Marshall combos ( build EL 34 ) depend from that the Vox has build
to class A ( more clear sound ) and Marshall class AB or B ( more
powerful sound at solos, but chords sounds always a little "muddy".
Also theres some differences on the character of distortion you can hear
when you play more loud volumes depend the different tubes...?

-Pentti

Funny how, maybe no one will have some experiences with these valve
types I asked. At least, EL 84 will expanse some presence frequencies
and EL 34 will make some more power on low end. Is this true?

It's a load of ********. Tubes don't have tone controls inside them.

You are right I think that the AC30 does run those EL84s with quite a high
quiescent current.

Graham

[mick]

On Tue, 21 Oct 2008 10:11:36 +0100, Eeyore wrote:

snip

You are right I think that the AC30 does run those EL84s with quite a
high quiescent current.



It's been many years since I last had dealings with an AC30, but IIRC it
ran the outputs pretty hot - you're probably right there.

--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info
Filtering everything posted from googlegroups to kill spam.

[Dominique Michel[_2_]]

Le Tue, 21 Oct 2008 08:32:42 +0200,
jh a écrit :

Dominique Michel schrieb:
Le Mon, 20 Oct 2008 23:49:12 +0200,
jh a écrit :

Dominique Michel schrieb:
Le Fri, 17 Oct 2008 18:16:27 GMT,
mick a écrit :

On Fri, 17 Oct 2008 15:40:50 +0300, PenttiL wrote:

PenttiL wrote:
Just ask. If there's an amp output push-pull stage planned to work four
EL 84 or two EL 34 and the class is the same, what are the differences
I can clearly hear depend the different character between the tubes?

I think the differences between the guitar amps Vox AC 30 ( EL 84 ) and
some Marshall combos ( build EL 34 ) depend from that the Vox has build
to class A ( more clear sound ) and Marshall class AB or B ( more
powerful sound at solos, but chords sounds always a little "muddy".
Also theres some differences on the character of distortion you can
hear when you play more loud volumes depend the different tubes...?

-Pentti
Funny how, maybe no one will have some experiences with these valve
types I asked. At least, EL 84 will expanse some presence frequencies
and EL 34 will make some more power on low end. Is this true?

Don't concentrate too much on the valve types. Both of those are similar
in many ways (the EL34 is the "big brother" of the EL84). Changes in the
circuit, including the OPT characteristics, the output stage biasing and
the capabilities of the driver stage will make such huge differences
that it's rather silly to make comparisons - at least of correctly
designed amps.

Guitar amps in particular are such a personal choice that all
comparisons become meaningless.

Some people claim that the EL84 sounds better in hi-fi applications,
even if it is under-powered. OTOH the EL34 is a workhorse valve,
designed for high output, and is probably better where power is
considered to be more important than sound quality. I'm not going to
give an opinion either way!

The bad sound quality of most high power all valves guitar amps doesn't
come from the valve types but from the driver stage that cannot drive the
needed power for the command grid of a class B output stage at full
volume driven by a guitar.

The signal from a guitar is not a sinus at all but have a very big pulse
of harmonics at the beginning of each period (especially with single
humbugging microphones). That implies that the command grid of a class B
push pull will become positive at high output during those pulses. I
don't know any commercial high power all valves guitar amp where the
driver is able to deliver the 2 or 3 watts (for a 6L6 or EL34 push-pull)
needed by the command grids of the output stage during those pulses.

To deliver that power will implies that the main supply will be able to
drive the output stage and that the output stage must be carefully
designed in order to handle this (the g2 can get very hot). This is
possible to archive, but not at the cost of a commercial guitar amp. And
even if you made your own such designed amp, the cost will be high.

You can even stabilize the G2 of the output stage of a class B guitar amp.
You will get an outstanding dynamic, and that even at full power, but this
have a cost and it will be very easy to blow the tubes and the transformer
if the circuit of all the parts is not very carefully designed.

As example, the most expansive marshall don't cost more as 100$ to
manufacture. If it was not the case, they would made something else.

Ciao,
Dominique

It's no surprise really that you aren't getting many replies. ;-)


.. dear dominique

might it be that the imperfections you cite *are* the reason, why so
many guitar players and musos swear on exactly those amps?

realistic sound reproduction and "perfect" ampifiers ain't what guitar
players like. Do yourself a favour an listen to one of those imperfect
amp (e.g. Fender 5E3 tweed deluxe or a 1987 50W Marshall) in the hands
of a really good musician. Give him a "real good" amp - hifi wise _ and
listen again......


Already done. Both are great commercial amps, but nothing more for me.Take a
look at the 5E2 schema. The driver have a high impedance output. That imply
that it cannot drive the grids of the output stage when they are in
saturation. Power tubes need power onto the grid in order to get a good
dynamic when this grid is into saturation.


the sound is pristine, but obviously not your piece of cake. I love my
5E3 and the guys at the local jam who also play it regularly do that
too... Of course this amp does not have 20k, it's more 12k or 15k, but
the speaker limits it to about 5k-6k anyway....

just my 2cts

regards

Jochen

You cannot compare a guitar amp with an hifi amp. A guitar amp is some kind
of power operational amplifier in open loop. (Even if the internal design is
completely different, they share many things like the gain, the ability to
fully saturate, and the limited bandwitch.) A few milivolts at the entry can
give you full output, it is a very huge gain, it have no feedback and you
can get saturation in all the stages. So, you just cannot compare it with
an hifi device.


Why? Compare the power amps of a tube hifi and a guit amp. Not that
different at all.


Oh yes, it is one big difference. You have feedback in a hifi amp, not in a
guitar amp.

The bias of the output stage is also different because a guitar amp can be
fully saturated during its normal use.



I am just talking here about a class B guitar amp with an outstanding
dynamic at full output, something that will drive the speaker into one
controlled jet reactor when playing at high volume. That will give you the
best of both sounds : a powerful saturation but with all the flavors of a
great clear sound at the same time.

? the natural compression is e.g. exactly what *I* like. Obviously
there's a lot of cakes on this planet and different tastes. The
assymetrical clip of a 5E3 PI gives you a lot of possibilities too.
Imperfection in perfection.


I was not even talking about the bandwitch of such amplifiers. Why do you
think that most guitar players in the world do have the treble knob almost
at the maximum gain, the middle know at a very low setting and the bass at a
relatively high setting? Only because their amps and their loudspeakers are
just good medium devices.


different styles. Not all of them do that. You won't play completly
scooped mids with a 70s 50W Marshall.... The classic and beloved first
early 60s Voxes did not even have a real treble knob.

the scoopers want the edge and aggression in the 4-8k region and a real
thump in the lower registers. Imho 10k-15k with overdrive sounds like
a wasp in the card box. But the speakers limit the higher freqs anyway...
The local feedback at the presence does it part too, by increasing the
distortion patterns ath higher freqs.


But it is normal. An operational amp in open loop like a guitar amp cannot
have a regular bandwitch between 20Hz to 20kHz. You will have to introduce
some kind of feedback for that, and feedback is definitely not what I like
into a guitar amp.


You have obviously not measured the real bandwidth of a guitar amp yet.

Yes, I done this measurement. As well that the measurement of an op amp in
open loop.


For the bandwitch, it is not many things you can do into the preamp. Triode
in class A without feedback do have limited bandwitch.

Not necessarily. A triode without feedback can easily go up to 60K

Do you measured the bandwitch of a triode in grounded cathode montage without
feedback? A high mu triode like the ECC83 will not be linear over 16k due to
Miller effect.


The type of tube will give
you some latitude : higher mu implies more facility to saturate but less
bandwitch.


Why saturate the preamp when you've got a power amp?

Why not ? The preamp doesn't have the same kind of saturation (asymmetrical
saturation) that the power stage (symmetrical class B) and I like it too. And I
am also not only playing at high volume.

What do you think? You put an guitar at the entry, one with a real passive
microphone, not one with an active microphone. Such good mic can give you pulses
over 2 volts. I measured that too. That imply that you will get
asymmetrical saturation on the input grid of the first valve when the guitar
volume is at the maximum. This is normal behaviour for a good guitar amp with a
good guitar mic at its entry.


But for the driver, you can use something like a class A EL84 in triode with
transformer coupling to the output. A very good quality transformer can
give you an outstanding bandwitch, but it will cost a lot of money and you
will not find such a circuit into a commercial guitar amp.


I have one on the bench at the moment...In this one the interstage
transformer is bigger than the OT of a champ. More like that of a super
reverb. Although it's one of the best amps I've ever heard and played
(clean) the buzz is not that grat, if driven.

Such a transformer will be a little
bigger that the output transformer of a fender champ, but it will be able to
drive the grids of 2 power tubes like EL34 when they are into saturation.