Looking at my tube inventory, I can't find
my old pair 6V6, but I do have a pair of 6L6.

Pin outs are the same .

I was going to bring up a old HealthKit 20amp mono block from storage this
week ...

? What'ch think ?

Well, looking at the schematic, it takes 6l6.

In article HPNle.6025$PR6.2409
@tornado.texas.rr.com,
says...
Looking at my tube inventory, I can't find
my old pair 6V6, but I do have a pair of 6L6.

Pin outs are the same .

I was going to bring up a old HealthKit 20amp mono block from storage this
week ...

? What'ch think ?

Filament supply amperage...how much difference?

CompUser wrote:
In article HPNle.6025$PR6.2409
@tornado.texas.rr.com,
says...

Looking at my tube inventory, I can't find
my old pair 6V6, but I do have a pair of 6L6.

Pin outs are the same .

I was going to bring up a old HealthKit 20amp mono block from storage this
week ...

? What'ch think ?


Filament supply amperage...how much difference?

Hi,
Double, 0.9 vs 0.45.
Tony

wb wrote:

Looking at my tube inventory, I can't find
my old pair 6V6, but I do have a pair of 6L6.

Pin outs are the same .

I was going to bring up a old HealthKit 20amp mono block from storage this
week ...

? What'ch think ?

6L6 has heaters = 0.9amps, 6V6 = 0.45amps.
Has the heater winding got the capability for the extra 0.9 amps.
Probably it has, but if in doubt, buy a 15 VA tranny with 6.3v output and run
all the heaters off that.

Then make sure the 6L6 don't draw more anode bias current than the 6V6.
That way you won't cook the OPT or PSU.
And then you may find that you will get a mild amount of extra po,
and that you could possibly connect the 6L6 in triode to get about the same po

as the 6V6 in beam tetrode mode.
If the tube rectifier is abolished and SS diodes put in the B+ will be higher
and give a wider voltage swing.
This won't damage the OPT although the LF pole at full power may be a little
higher.
But again, don't let Ia be more than 40 mA, same as for 6V6.
The PT won't be dissipating any extra power with the silicon diodes.
You can even use fixed bias, making B+ effectively even higher.
The higher B+ will improve the 6L6 triode performance.

Patrick Turner.

wb wrote:

Well, looking at the schematic, it takes 6l6.

Well DUHH, use a ferkin pair of 6L6.

Patrick Turner.

Patrick Turner wrote:

wb wrote:


Looking at my tube inventory, I can't find
my old pair 6V6, but I do have a pair of 6L6.

Pin outs are the same .

I was going to bring up a old HealthKit 20amp mono block from storage this
week ...

? What'ch think ?


6L6 has heaters = 0.9amps, 6V6 = 0.45amps.
Has the heater winding got the capability for the extra 0.9 amps.
Probably it has, but if in doubt, buy a 15 VA tranny with 6.3v output and run
all the heaters off that.

Then make sure the 6L6 don't draw more anode bias current than the 6V6.
That way you won't cook the OPT or PSU.
And then you may find that you will get a mild amount of extra po,
and that you could possibly connect the 6L6 in triode to get about the same po

as the 6V6 in beam tetrode mode.
If the tube rectifier is abolished and SS diodes put in the B+ will be higher
and give a wider voltage swing.
This won't damage the OPT although the LF pole at full power may be a little
higher.
But again, don't let Ia be more than 40 mA, same as for 6V6.
The PT won't be dissipating any extra power with the silicon diodes.
You can even use fixed bias, making B+ effectively even higher.
The higher B+ will improve the 6L6 triode performance.

Patrick Turner.


Hi,
What is anode bias current?
Tony

Indeed, filament current is the double. For all the rest, they should be
pretty OK. (BTW the 6V6 is a brilliant tube, I'd just get a pair of JJ or
similar for maybe 30$, it's not such an expense..)

Ciao

Fabio


"wb" ha scritto nel messaggio
...
Looking at my tube inventory, I can't find
my old pair 6V6, but I do have a pair of 6L6.

Pin outs are the same .

I was going to bring up a old HealthKit 20amp mono block from storage this
week ...

? What'ch think ?

Well DUHH, use a ferkin pair of 6L6.


Yeah ,,, I know ... I didn't want someone to flame me saying
"DUHHH ... It takes 6l6! " I haven't looked at the amp in 6 months
and for some reason I just considered a 20W amp as 6v6 .

Thanks and give that girl needs a cheese burger:

http://www.officialunknownhinson.com...y.01_Bband.mov

Hi,
Double, 0.9 vs 0.45.
Man , Almost 2 amp draw just for the heaters .. !

Tony Hwang wrote:

Patrick Turner wrote:

wb wrote:


Looking at my tube inventory, I can't find
my old pair 6V6, but I do have a pair of 6L6.

Pin outs are the same .

I was going to bring up a old HealthKit 20amp mono block from storage this
week ...

? What'ch think ?


6L6 has heaters = 0.9amps, 6V6 = 0.45amps.
Has the heater winding got the capability for the extra 0.9 amps.
Probably it has, but if in doubt, buy a 15 VA tranny with 6.3v output and run
all the heaters off that.

Then make sure the 6L6 don't draw more anode bias current than the 6V6.
That way you won't cook the OPT or PSU.
And then you may find that you will get a mild amount of extra po,
and that you could possibly connect the 6L6 in triode to get about the same po

as the 6V6 in beam tetrode mode.
If the tube rectifier is abolished and SS diodes put in the B+ will be higher
and give a wider voltage swing.
This won't damage the OPT although the LF pole at full power may be a little
higher.
But again, don't let Ia be more than 40 mA, same as for 6V6.
The PT won't be dissipating any extra power with the silicon diodes.
You can even use fixed bias, making B+ effectively even higher.
The higher B+ will improve the 6L6 triode performance.

Patrick Turner.


Hi,
What is anode bias current?
Tony

When the amp is just sitting there, turned on, but with no signal,
there will be a current flow through each and every tube from anode to cathode.
This is called the idle current or bias or quiescent current.
In a 6L6 which has 350v of dc voltage at idle between its anode and cathode
the **bias current** might be typically 40 mA.
The heat liberated in the tube at the anode is measured in watts of heat energy,
like a lightbulb, and will be ( 350V x 0.04A ) = 14 watts in this case.
There is 6.3v at 0.9A of heat liberated in the cathode heater, ie, 5.7 watts.
There is a bias current flow in the screen circuit, and this current is about 5% to
10%
of the anode current, depending on the screen supply voltage.
So perhaps screen heat production is 2 watts.

Total heat from the tube just sitting there doing nothing = 14 + 5.7 + 2 = 21.7
watts.

The bias currents do not change a lot during normal tube operation.
But added to the bias currents are signal currents, and a maximum plate current
may be up to say 400mA, and down to 0.0mA, or to what is called "cut off".

You should read more old books about how tubes work.

Patrick Turner.

wb wrote:


Well DUHH, use a ferkin pair of 6L6.


Yeah ,,, I know ... I didn't want someone to flame me saying
"DUHHH ... It takes 6l6! " I haven't looked at the amp in 6 months
and for some reason I just considered a 20W amp as 6v6 .

Well, Mesa Boogie get 21 watts at clipping from a pair of 6V6.
But they use about 450v applied to plate and screens.

It much more civilised to get that many watts from a pair of 6L6;
in fact 50 watts is possible...but not if the amp was set up for
6V6 in the first place, where 350v may be the B+.
But with 350v between anode and cathode, 20 watts of class A1 with 6L6
is possible in beam tetrode mode, and around 10 watts in triode, class
A1.

Probably a lot more than 21 watts from two 6V6 is possible.
I am not sure what the maximum anode supply voltage can be, but I guess
its the same as 6BQ5, where 700v can be applied on the anodes, 350v to
the screens.
and the RLa-a = 14k, and po = 36 watts.
Musical Reference achieve this, and I have measured it myself.
Its basically all class B1 of course.
The latest 6V6 have quite high voltage ratings for the screens.

Patrick Turner.

wb wrote:


Hi,
Double, 0.9 vs 0.45.
Man , Almost 2 amp draw just for the heaters .. !

Dat nothing man, try 12 x 6550, they draw 6.3 volts x 21.6 amps.

Patrick Turner.

Patrick Turner wrote:

Tony Hwang wrote:


Patrick Turner wrote:

wb wrote:



Looking at my tube inventory, I can't find
my old pair 6V6, but I do have a pair of 6L6.

Pin outs are the same .

I was going to bring up a old HealthKit 20amp mono block from storage this
week ...

? What'ch think ?


6L6 has heaters = 0.9amps, 6V6 = 0.45amps.
Has the heater winding got the capability for the extra 0.9 amps.
Probably it has, but if in doubt, buy a 15 VA tranny with 6.3v output and run
all the heaters off that.

Then make sure the 6L6 don't draw more anode bias current than the 6V6.
That way you won't cook the OPT or PSU.
And then you may find that you will get a mild amount of extra po,
and that you could possibly connect the 6L6 in triode to get about the same po

as the 6V6 in beam tetrode mode.
If the tube rectifier is abolished and SS diodes put in the B+ will be higher
and give a wider voltage swing.
This won't damage the OPT although the LF pole at full power may be a little
higher.
But again, don't let Ia be more than 40 mA, same as for 6V6.
The PT won't be dissipating any extra power with the silicon diodes.
You can even use fixed bias, making B+ effectively even higher.
The higher B+ will improve the 6L6 triode performance.

Patrick Turner.



Hi,
What is anode bias current?
Tony


When the amp is just sitting there, turned on, but with no signal,
there will be a current flow through each and every tube from anode to cathode.
This is called the idle current or bias or quiescent current.
In a 6L6 which has 350v of dc voltage at idle between its anode and cathode
the **bias current** might be typically 40 mA.
The heat liberated in the tube at the anode is measured in watts of heat energy,
like a lightbulb, and will be ( 350V x 0.04A ) = 14 watts in this case.
There is 6.3v at 0.9A of heat liberated in the cathode heater, ie, 5.7 watts.
There is a bias current flow in the screen circuit, and this current is about 5% to
10%
of the anode current, depending on the screen supply voltage.
So perhaps screen heat production is 2 watts.

Total heat from the tube just sitting there doing nothing = 14 + 5.7 + 2 = 21.7
watts.

The bias currents do not change a lot during normal tube operation.
But added to the bias currents are signal currents, and a maximum plate current
may be up to say 400mA, and down to 0.0mA, or to what is called "cut off".

You should read more old books about how tubes work.

Patrick Turner.

Hi,
I see bias current, then we're talking about AB2 class amp operation?
I am ~65 years old. Went to school in the days of tubes, nothing but
tubes. Evolved thru integrated circuits. Retired in '96.
Thanks for run down on the tube basics. It was a refresher for sure.
Tony

I suspect 20 Watts from a pair of 6L6's is correct for a Heathkit. The
plate voltage will tell you. If around 350 v with no tubes in it, go
ahead with the 6L6's. You'd need 450 vdc, well over 400 to get 20 W
from 6V6's Butt... don't just do what I say. It's just that these amps
are not tweaked for max output the way guitar amps tend to be.

Porky

Patrick Turner wrote:

wb wrote:


Well DUHH, use a ferkin pair of 6L6.


Yeah ,,, I know ... I didn't want someone to flame me saying
"DUHHH ... It takes 6l6! " I haven't looked at the amp in 6 months
and for some reason I just considered a 20W amp as 6v6 .

Well, Mesa Boogie get 21 watts at clipping from a pair of 6V6.
But they use about 450v applied to plate and screens.

It much more civilised to get that many watts from a pair of 6L6;
in fact 50 watts is possible...but not if the amp was set up for
6V6 in the first place, where 350v may be the B+.
But with 350v between anode and cathode, 20 watts of class A1 with 6L6
is possible in beam tetrode mode, and around 10 watts in triode, class
A1.

Probably a lot more than 21 watts from two 6V6 is possible.
I am not sure what the maximum anode supply voltage can be, but I guess
its the same as 6BQ5, where 700v can be applied on the anodes, 350v to
the screens.
and the RLa-a = 14k, and po = 36 watts.
Musical Reference achieve this, and I have measured it myself.
Its basically all class B1 of course.
The latest 6V6 have quite high voltage ratings for the screens.

Patrick Turner.

You can get a lot of power from PP 6V6's running AB2 at reasonable
voltages. Even better, the Rla-a load doesn't & shouldn't be high as in
your example. Drive is easy by way of a direct drive PP CF pair. I've done
it.

But don't try to run them CW. That might cause meltdown!

Cheers, John Stewart

The bias currents do not change a lot during normal tube operation.
But added to the bias currents are signal currents, and a maximum plate current
may be up to say 400mA, and down to 0.0mA, or to what is called "cut off".

You should read more old books about how tubes work.

Patrick Turner.

Hi,
I see bias current, then we're talking about AB2 class amp operation?

If you did have Ia max = 400mA, and Ia minimum = 0.0 mA,
then the tube would be working in class AB1, maybe AB2, depending on load.

For class A operation, the increase in Ia in a tube is approximately the same
as the amount of reduction of Ia with a sine wave.
The tube does not reduce its current flowing through it or the load to 0.0mA,
and nor does the tube stall the increase in current due to clipping, so in effect
any tube in class A ia always actively providing voltage and current changes in the load
to which it is connected.

Tubes, like people and anything else are not perfect, and for a given +ve or -ve grid
input voltage they usually conduct more current with +ve input voltage
than the amount of current reduction with a -ve input voltage of the same magnitude,
and this leads to some distortion of the output signal, even though the tube is set
up to work in its most linear working region.

So for a 6L6 in triode, we may arrange the Ea = 350v, and have Ia + Ig2 = 71 mA,
and this gives a triode plate dissipation at idle = 25 watts.
If one uses a load of 2.1k, you will get a load voltage swing
of -140v, and +120v, which is a peak to peak swing of 260v = 92vrms =
4.0 watts.

The above calculations are taken from a rough loadline analysis.

The mainly second harmonic distortion = ( 140 - 120 ) / ( 2 x [ 140 + 120 ] ) = 3.8%

Your old books will show how to draw loadlines to establish how much power
and 2nd harmonic distortion you will get.

With two tubes in PP, each one might be rigged to see 2.1k, and then the
load measured from anode to anode is 4.2k, and you will get 8 watts of pure class A.
Lower load values will make the amp operate in class AB, and higher loads make it operate

only in class A.



I am ~65 years old. Went to school in the days of tubes, nothing but
tubes. Evolved thru integrated circuits. Retired in '96.
Thanks for run down on the tube basics. It was a refresher for sure.
Tony

The books will bring things back faster than I can, or have time for.

Patrick Turner.

John Stewart wrote:

Patrick Turner wrote:

wb wrote:


Well DUHH, use a ferkin pair of 6L6.


Yeah ,,, I know ... I didn't want someone to flame me saying
"DUHHH ... It takes 6l6! " I haven't looked at the amp in 6 months
and for some reason I just considered a 20W amp as 6v6 .

Well, Mesa Boogie get 21 watts at clipping from a pair of 6V6.
But they use about 450v applied to plate and screens.

It much more civilised to get that many watts from a pair of 6L6;
in fact 50 watts is possible...but not if the amp was set up for
6V6 in the first place, where 350v may be the B+.
But with 350v between anode and cathode, 20 watts of class A1 with 6L6
is possible in beam tetrode mode, and around 10 watts in triode, class
A1.

Probably a lot more than 21 watts from two 6V6 is possible.
I am not sure what the maximum anode supply voltage can be, but I guess
its the same as 6BQ5, where 700v can be applied on the anodes, 350v to
the screens.
and the RLa-a = 14k, and po = 36 watts.
Musical Reference achieve this, and I have measured it myself.
Its basically all class B1 of course.
The latest 6V6 have quite high voltage ratings for the screens.

Patrick Turner.

You can get a lot of power from PP 6V6's running AB2 at reasonable
voltages. Even better, the Rla-a load doesn't & shouldn't be high as in
your example. Drive is easy by way of a direct drive PP CF pair. I've done
it.

The 36 watts into 14k from 2 x 6BQ5 is 709 vrms a-a, or 350vrms at each
anode = 500 peak v swing, class AB1, but as far as I know the EL84, ( and EL34
)
don't like being driven into grid current regions.
Hence to get such high power, high Ea, and high RL values are needed.

6V6 would manage the same v swing at least, same load, same Ea class AB1.

But one could indeed get much more max po with a lower RL and Ea
because of the ease and substantial linearity of class AB2 when driving the
grids
up to maybe 15v positive. Methinks the higher RL and Ea will give the best
linearity and lowest Ro.

I have not seen a class AB2 guitar amp yet.
Its because these amos are regularly heavily over driven, and the grid
dissipation limits can be exceeded when driven with cathode followers.
Class AB2 for guitar amps is not a good idea. Use more/bigger tubes for more
power,
do not flog hell out of too few tubes.


But don't try to run them CW. That might cause meltdown!

CW, Cathode Wobbly.

Patrick Turner.



Cheers, John Stewart

Patrick Turner wrote:

The bias currents do not change a lot during normal tube operation.
But added to the bias currents are signal currents, and a maximum plate current
may be up to say 400mA, and down to 0.0mA, or to what is called "cut off".

You should read more old books about how tubes work.

Patrick Turner.


Hi,
I see bias current, then we're talking about AB2 class amp operation?


If you did have Ia max = 400mA, and Ia minimum = 0.0 mA,
then the tube would be working in class AB1, maybe AB2, depending on load.

For class A operation, the increase in Ia in a tube is approximately the same
as the amount of reduction of Ia with a sine wave.
The tube does not reduce its current flowing through it or the load to 0.0mA,
and nor does the tube stall the increase in current due to clipping, so in effect
any tube in class A ia always actively providing voltage and current changes in the load
to which it is connected.

Tubes, like people and anything else are not perfect, and for a given +ve or -ve grid
input voltage they usually conduct more current with +ve input voltage
than the amount of current reduction with a -ve input voltage of the same magnitude,
and this leads to some distortion of the output signal, even though the tube is set
up to work in its most linear working region.

So for a 6L6 in triode, we may arrange the Ea = 350v, and have Ia + Ig2 = 71 mA,
and this gives a triode plate dissipation at idle = 25 watts.
If one uses a load of 2.1k, you will get a load voltage swing
of -140v, and +120v, which is a peak to peak swing of 260v = 92vrms =
4.0 watts.

The above calculations are taken from a rough loadline analysis.

The mainly second harmonic distortion = ( 140 - 120 ) / ( 2 x [ 140 + 120 ] ) = 3.8%

Your old books will show how to draw loadlines to establish how much power
and 2nd harmonic distortion you will get.

With two tubes in PP, each one might be rigged to see 2.1k, and then the
load measured from anode to anode is 4.2k, and you will get 8 watts of pure class A.
Lower load values will make the amp operate in class AB, and higher loads make it operate

only in class A.



I am ~65 years old. Went to school in the days of tubes, nothing but
tubes. Evolved thru integrated circuits. Retired in '96.
Thanks for run down on the tube basics. It was a refresher for sure.
Tony


The books will bring things back faster than I can, or have time for.

Patrick Turner.


Hi,
Thank you so much. You know what? When wheat ripes in the field it bows
it's head. If you think you can run, there is a guy who can fly.
Ever heard of this old sayings?
Tony

Tony Hwang wrote:

Patrick Turner wrote:

The bias currents do not change a lot during normal tube operation.
But added to the bias currents are signal currents, and a maximum plate current
may be up to say 400mA, and down to 0.0mA, or to what is called "cut off".

You should read more old books about how tubes work.

Patrick Turner.


Hi,
I see bias current, then we're talking about AB2 class amp operation?


If you did have Ia max = 400mA, and Ia minimum = 0.0 mA,
then the tube would be working in class AB1, maybe AB2, depending on load.

For class A operation, the increase in Ia in a tube is approximately the same
as the amount of reduction of Ia with a sine wave.
The tube does not reduce its current flowing through it or the load to 0.0mA,
and nor does the tube stall the increase in current due to clipping, so in effect
any tube in class A ia always actively providing voltage and current changes in the load
to which it is connected.

Tubes, like people and anything else are not perfect, and for a given +ve or -ve grid
input voltage they usually conduct more current with +ve input voltage
than the amount of current reduction with a -ve input voltage of the same magnitude,
and this leads to some distortion of the output signal, even though the tube is set
up to work in its most linear working region.

So for a 6L6 in triode, we may arrange the Ea = 350v, and have Ia + Ig2 = 71 mA,
and this gives a triode plate dissipation at idle = 25 watts.
If one uses a load of 2.1k, you will get a load voltage swing
of -140v, and +120v, which is a peak to peak swing of 260v = 92vrms =
4.0 watts.

The above calculations are taken from a rough loadline analysis.

The mainly second harmonic distortion = ( 140 - 120 ) / ( 2 x [ 140 + 120 ] ) = 3.8%

Your old books will show how to draw loadlines to establish how much power
and 2nd harmonic distortion you will get.

With two tubes in PP, each one might be rigged to see 2.1k, and then the
load measured from anode to anode is 4.2k, and you will get 8 watts of pure class A.
Lower load values will make the amp operate in class AB, and higher loads make it operate

only in class A.



I am ~65 years old. Went to school in the days of tubes, nothing but
tubes. Evolved thru integrated circuits. Retired in '96.
Thanks for run down on the tube basics. It was a refresher for sure.
Tony


The books will bring things back faster than I can, or have time for.

Patrick Turner.


Hi,
Thank you so much. You know what? When wheat ripes in the field it bows
it's head. If you think you can run, there is a guy who can fly.
Ever heard of this old sayings?
Tony

A head full of knowledge bows to the god who designed the brain.

And if one can fly, beware of a crash.

Patrick Turner.

Patrick Turner wrote:

Tony Hwang wrote:


Patrick Turner wrote:


The bias currents do not change a lot during normal tube operation.
But added to the bias currents are signal currents, and a maximum plate current
may be up to say 400mA, and down to 0.0mA, or to what is called "cut off".

You should read more old books about how tubes work.

Patrick Turner.


Hi,
I see bias current, then we're talking about AB2 class amp operation?


If you did have Ia max = 400mA, and Ia minimum = 0.0 mA,
then the tube would be working in class AB1, maybe AB2, depending on load.

For class A operation, the increase in Ia in a tube is approximately the same
as the amount of reduction of Ia with a sine wave.
The tube does not reduce its current flowing through it or the load to 0.0mA,
and nor does the tube stall the increase in current due to clipping, so in effect
any tube in class A ia always actively providing voltage and current changes in the load
to which it is connected.

Tubes, like people and anything else are not perfect, and for a given +ve or -ve grid
input voltage they usually conduct more current with +ve input voltage
than the amount of current reduction with a -ve input voltage of the same magnitude,
and this leads to some distortion of the output signal, even though the tube is set
up to work in its most linear working region.

So for a 6L6 in triode, we may arrange the Ea = 350v, and have Ia + Ig2 = 71 mA,
and this gives a triode plate dissipation at idle = 25 watts.
If one uses a load of 2.1k, you will get a load voltage swing
of -140v, and +120v, which is a peak to peak swing of 260v = 92vrms =
4.0 watts.

The above calculations are taken from a rough loadline analysis.

The mainly second harmonic distortion = ( 140 - 120 ) / ( 2 x [ 140 + 120 ] ) = 3.8%

Your old books will show how to draw loadlines to establish how much power
and 2nd harmonic distortion you will get.

With two tubes in PP, each one might be rigged to see 2.1k, and then the
load measured from anode to anode is 4.2k, and you will get 8 watts of pure class A.
Lower load values will make the amp operate in class AB, and higher loads make it operate

only in class A.




I am ~65 years old. Went to school in the days of tubes, nothing but
tubes. Evolved thru integrated circuits. Retired in '96.
Thanks for run down on the tube basics. It was a refresher for sure.
Tony


The books will bring things back faster than I can, or have time for.

Patrick Turner.



Hi,
Thank you so much. You know what? When wheat ripes in the field it bows
it's head. If you think you can run, there is a guy who can fly.
Ever heard of this old sayings?
Tony


A head full of knowledge bows to the god who designed the brain.

And if one can fly, beware of a crash.

Patrick Turner.




Hi,
Good. You're speaking for yourself. That is very good.
Tony

John Stewart wrote:

You can get a lot of power from PP 6V6's running AB2 at reasonable
voltages. Even better, the Rla-a load doesn't & shouldn't be high as in
your example. Drive is easy by way of a direct drive PP CF pair. I've done
it.

I'm confident you'll find if you look more closely as I & others have,
that there's no practical pwr advantage of AB2 over AB1 with small
pentodes & even somewhat of a loss. This is because the same or more
pwr at the same THD is available within the dissipation limit at a
higher AB1 Eo, compared to the performance of AB2 at a necessarily
lower Eo required to maintain the same limit. In a practical sense,
AB2 often isn't justifiable for pwr increase until we get to tubes
which can tolerate a lot more G1 dissipation while staying within the
rest of its dissipation limits.

But don't try to run them CW. That might cause meltdown!

Unsure what you mean by CW - if you mean RF CW, that's often a lower
level of service than a typical AF pwr stage may be due to key-up time.
The 6V6 has also been used very reliably but at modest power as a
small PP Class B modulator. I have an early WW2 aircraft xtmr (also in
use since 1939) that uses 6V6's in both of these ways, for either CW or
AM phone, so all of these are very old ideas proven commercially when
the tube was a brand new product originally designed for low drain
performance in battery powered radio gear.

wrote:

John Stewart wrote:

You can get a lot of power from PP 6V6's running AB2 at reasonable
voltages. Even better, the Rla-a load doesn't & shouldn't be high as in
your example. Drive is easy by way of a direct drive PP CF pair. I've done
it.

I'm confident you'll find if you look more closely as I & others have,
that there's no practical pwr advantage of AB2 over AB1 with small
pentodes & even somewhat of a loss. This is because the same or more
pwr at the same THD is available within the dissipation limit at a
higher AB1 Eo, compared to the performance of AB2 at a necessarily
lower Eo required to maintain the same limit. In a practical sense,
AB2 often isn't justifiable for pwr increase until we get to tubes
which can tolerate a lot more G1 dissipation while staying within the
rest of its dissipation limits.

But don't try to run them CW. That might cause meltdown!

Unsure what you mean by CW - if you mean RF CW, that's often a lower
level of service than a typical AF pwr stage may be due to key-up time.
The 6V6 has also been used very reliably but at modest power as a
small PP Class B modulator. I have an early WW2 aircraft xtmr (also in
use since 1939) that uses 6V6's in both of these ways, for either CW or
AM phone, so all of these are very old ideas proven commercially when
the tube was a brand new product originally designed for low drain
performance in battery powered radio gear.

I finally got some time to do some actual measurements on this subject. The time
was available today since at 34 C it is to damned hot to work outside!

The amplifier I used for these tests was the one I mentioned earlier. The output
is PP 6V6GT's into a Hammond 125E OPT. Drive is thru a PP CF using a 6BQ7,
straight into the control grids of the PP output pair, so I can avoid the
troublesome IT.

The measurement of output power & power dissipated in the G1 of one of the
6V6GT's is by a pair of MetraHit 29S Precision DMM & Wattmeters.

See
http://www.gmc-instruments.com/engli...e/metrahi1.htm

The idle current of each 6V6GT is 40 ma.

The signal trace for grid drive (blue) & grid current (red) is over at ABSE
labelled Class AB2. For that result the plate to plate load was set at 4.2K. You
can see that the grid bias is about -20 volts. The grid current trace is the
voltage drop across a 100R, 1/2 W resistor. It looks like the peak control grid
current is not quite 11 ma. That would be 1.1 volts across the 100R sampling
resistor. That drop was processed thru a Pico Tech M1053 Differential Probe. The
A to D was thru a Pico Tech ADC-216.

See
http://www.picotech.com/audio_spectrum_analyzer.html

In order to avoid errors caused by frequency limitations in the test equipment I
used a signal of 100 Hz. That way the harmonics in the grid current should not
be a problem.

With the 4.2 K load the 6V6GT's go into AB2 at 9 watts output while the plate
supply was 324 volts. Max output in this mode was 22 watts where the plate
supply had dropped to 314 volts. Input to each 6V6GT control grid measured 26
milliwatts on the MetraHit 29S Wattmeter.

For an 8.2 K plate to plate load AB2 operation was not possible since the load
line bumped up into the diode line of each tube. The max output was 15 watts
while the plate supply was 323 volts.

CW is just that, Continuous Wave, something not normally encountered in music or
speech. So one can run quite successfully with large peak power but rather
ordinary average power. That keeps most of the operating conditions within safe
limits, both for the equipment & the operator. CW in the RF sense is not what I
am referring to in this example. My point is simply max power or close to it on
a continuous basis. For many classes of operation min power dissipated is often
while large power is delivered to the load. The 6V6 & other tubes, in particular
the 807 are very useful as Class B modulators where both grids one & two are
driven by the audio signal. One can even get quite a bit of audio power out of
single or pair of 12AX7's connected PP for use as a speech modulator. But the
quality may not be what we like to call 'hifi'!

Cheers, John Stewart

John Stewart wrote:
wrote:

John Stewart wrote:

You can get a lot of power from PP 6V6's running AB2 at reasonable
voltages. Even better, the Rla-a load doesn't & shouldn't be high as in
your example. Drive is easy by way of a direct drive PP CF pair. I've done
it.

I'm confident you'll find if you look more closely as I & others have,
that there's no practical pwr advantage of AB2 over AB1 with small
pentodes & even somewhat of a loss.

(John's long and excellent hands-on research post snipped)

But John, a conclusion to your efforts is omitted.

Do you disagree that the same 22w in AB1 is attainable and easier (and
done every day as well)?

ISTM (so far at least) that you've done an excellent of demonstrating
it by proving the other side of he case.

Yes, we also have many examples of the tube as a PP class B modulator
(WW2 light aircraft gear comes first to mind & I have run such a rig
here myself for fun). I fail to see a direct relevance of this to the
subject, though.

wrote:

John Stewart wrote:
wrote:

John Stewart wrote:

You can get a lot of power from PP 6V6's running AB2 at reasonable
voltages. Even better, the Rla-a load doesn't & shouldn't be high as in
your example. Drive is easy by way of a direct drive PP CF pair. I've done
it.

I'm confident you'll find if you look more closely as I & others have,
that there's no practical pwr advantage of AB2 over AB1 with small
pentodes & even somewhat of a loss.

(John's long and excellent hands-on research post snipped)

But John, a conclusion to your efforts is omitted.

Do you disagree that the same 22w in AB1 is attainable and easier (and
done every day as well)?

Musical Reference amps using a 700v anode supply
350v screen supply, and a pair of 6BQ5 manage 36 watts in AB1.
And this was a low thd hi-fi amp.

RLa-a is 14k.

Patrick Turner.



ISTM (so far at least) that you've done an excellent of demonstrating
it by proving the other side of he case.

Yes, we also have many examples of the tube as a PP class B modulator
(WW2 light aircraft gear comes first to mind & I have run such a rig
here myself for fun). I fail to see a direct relevance of this to the
subject, though.

Unsure what you mean by CW - if you mean RF CW, that's often a lower
level of service than a typical AF pwr stage may be due to key-up time.


In general, most tube RF CW transmitters will be rated for a 50% duty
cycle.
So they are expected to rest half the time, pulling only idle
current...

The 6V6 has also been used very reliably but at modest power as a
small PP Class B modulator. I have an early WW2 aircraft xtmr (also in
use since 1939) that uses 6V6's in both of these ways, for either CW or
AM phone, so all of these are very old ideas proven commercially when
the tube was a brand new product originally designed for low drain
performance in battery powered radio gear.

Hummmm. I never considered the 6v6 that much of a low drain tube...
When I think of those, I think of the usual 1 volters you see in old
zenith transoceanics, etc...
The 6v6 is a handy tube...Loads were in the old audio amps, and tape
recorders, etc.. I built my first ham transmitter using a single 6v6,
built on
a ww2 navy surplus chassis. Had two versions...One, just line voltage
for
plate, and another with about a 350v tranny...When I keyed up, "CW",
you could see the tube glow blue in places...I used that on
40m.."7mhz".
That was in 1971, when I was in 8th grade, and I used the design from a
1949 ARRL handbook...So using 6v6's for rf in the 40's was as popular
as for audio amps... I've still got a few of the old metal 6v6's...I've
got a
1948 RCA console, with a dual 6v6 amp...Pretty high end for it's day..
Would make a great geetar amp I bet...All you gotta do is just unhook
the cable to the turntable, and plug it to a geetar I would think...But
it needs
a new output tranny...It worked for about an hour, after sitting up for
ages,
but crapped out due to the "green" oxidation, which shorts the
windings..
Need to get another, as it's a great sounding old radio...Has a 12 inch

speaker, with the usual MW-SW radio, and "victrola" turntable. It's
got the
old metal RCA's in it...Got another one sitting here on the table....
I was thinking about building some kinda champ clone using it...If it's
bad,
I got some glass ones...I've never tested it...And I got two good tube
checkers...
Lazy I am...I bet it still works though.... :/
MK

On Sat, 25 Jun 2005 07:08:32 GMT, Patrick Turner
wrote:

Musical Reference amps using a 700v anode supply
350v screen supply, and a pair of 6BQ5 manage 36 watts in AB1.
And this was a low thd hi-fi amp.

RLa-a is 14k.

Makes ya wonder how much output ya could get with 1000
volts plate supply to a pair of 6BQ5's.

WTF is "Musical Reference"?

Chris Hornbeck
"I can build you a test that will show either one. Which would you prefer
me to demonstrate?
--scott

Chris Hornbeck wrote:

On Sat, 25 Jun 2005 07:08:32 GMT, Patrick Turner
wrote:

Musical Reference amps using a 700v anode supply
350v screen supply, and a pair of 6BQ5 manage 36 watts in AB1.
And this was a low thd hi-fi amp.

RLa-a is 14k.

Makes ya wonder how much output ya could get with 1000
volts plate supply to a pair of 6BQ5's.

I wouldn't be wondering this at all, since 1,000v plate supply is a bit over
the top
and I wouldn't do it.

But they did make amps using EL34 and KT88 with 800v supplies.
The TT21 which is a KT88 with a top cap was a great tube to use
for a high voltage class AB amp and it'd put out 140 watts class AB2.



WTF is "Musical Reference"?

The brand name of a lesser known american made amp.
I serviced and tested one about 5 years ago, so I know it made 36 watts.

Patrick Turner.




Chris Hornbeck
"I can build you a test that will show either one. Which would you prefer
me to demonstrate?
--scott

wrote:

John Stewart wrote:
wrote:

John Stewart wrote:

You can get a lot of power from PP 6V6's running AB2 at reasonable
voltages. Even better, the Rla-a load doesn't & shouldn't be high as in
your example. Drive is easy by way of a direct drive PP CF pair. I've done
it.

I'm confident you'll find if you look more closely as I & others have,
that there's no practical pwr advantage of AB2 over AB1 with small
pentodes & even somewhat of a loss.

(John's long and excellent hands-on research post snipped)

But John, a conclusion to your efforts is omitted.

But what conclusion is necessary? I simply explained my point. As above, here is
what I had originally said in this thread-

----------------------------------------------------------------------------------

You can get a lot of power from PP 6V6's running AB2 at reasonable
voltages. Even better, the Rla-a load doesn't & shouldn't be high as in
your example. Drive is easy by way of a direct drive PP CF pair. I've done it.

But don't try to run them CW. That might cause meltdown!

------------------------------------------------------------------------------------



Do you disagree that the same 22w in AB1 is attainable and easier (and
done every day as well)?

There are many roads to Rome. I stated another possible hookup that avoids high
voltages. It also has the very important advantage of using an OPT of lower
impedance. That also is an important design consideration since it is easier to get
bandwidth at lower impedance's.

ISTM (so far at least) that you've done an excellent of demonstrating
it by proving the other side of he case.

Which other side? There are many more than just two possibilities here. It can be
demonstrated that each will have some design and/or cost advantage.

Yes, we also have many examples of the tube as a PP class B modulator
(WW2 light aircraft gear comes first to mind & I have run such a rig
here myself for fun). I fail to see a direct relevance of this to the
subject, though.

Better look back at your previous post. My points in respect to your last remark
were in response to those. Here it is-

-----------------------------------------------------------------------------------------------

Unsure what you mean by CW - if you mean RF CW, that's often a lower
level of service than a typical AF pwr stage may be due to key-up time.
The 6V6 has also been used very reliably but at modest power as a
small PP Class B modulator. I have an early WW2 aircraft xtmr (also in
use since 1939) that uses 6V6's in both of these ways, for either CW or
AM phone, so all of these are very old ideas proven commercially when
the tube was a brand new product originally designed for low drain
performance in battery powered radio gear.

--------------------------------------------------------------------------------------------------



Anyway, here is more data for the faithful (and others) to ponder!

6V6GT's PP into 4.2K

Power Watts THD %

5 0.57
9 Enters Class AB2
10 0.75
15 1.90
20 2.50

The same amplifier into 8.2K

5 0.51
10 0.54
15 0.65
20 Not possible

The amplifier has not been optimized at all. The THD measurements were made using an
HP 334A Analyzer. The signal source is an HP 200CD.

If you look carefully at the trace of control grid voltage I posted a few days ago
you can see a break or discontinuity where grid current starts to flow.

Another important point to keep in mind so far as using a CF driver is concerned is
that it provides a much lower impedance source with which to drive the following
grid than the same tube as a plate connected driver. In this example, when driving
10 ma into the 6V6GT grid one each half of the 6BQ7 has a G of about 7 ma/volt. As a
source that translates to of about 150R, much better than you can do with a plate
driven driver. Furthermore, it can run from DC to several hundred khz, not possible
at all with an IT.

Something to think about!!

Cheers, John Stewart

Patrick Turner wrote:

Chris Hornbeck wrote:

On Sat, 25 Jun 2005 07:08:32 GMT, Patrick Turner
wrote:

Musical Reference amps using a 700v anode supply
350v screen supply, and a pair of 6BQ5 manage 36 watts in AB1.
And this was a low thd hi-fi amp.

RLa-a is 14k.

Makes ya wonder how much output ya could get with 1000
volts plate supply to a pair of 6BQ5's.

I wouldn't be wondering this at all, since 1,000v plate supply is a bit over
the top
and I wouldn't do it.

I would be concerned about the 9-pin socket. What about flashover? Any kind of
grunge on the socket would cause fireworks.
The OPT too. The peak voltages at max signal level will be about 1.8X the
supply.

But they did make amps using EL34 and KT88 with 800v supplies.
The TT21 which is a KT88 with a top cap was a great tube to use
for a high voltage class AB amp and it'd put out 140 watts class AB2.

I built an amp using four of 6CD6GA's in PPP with 980 volts on the plates about
45 years ago. It managed an easy 120 watts. But not really safe for your living
room!!

Cheers, John Stewart

John Stewart wrote:

wrote:

John Stewart wrote:
wrote:

John Stewart wrote:

You can get a lot of power from PP 6V6's running AB2 at
reasonable
voltages. Even better, the Rla-a load doesn't & shouldn't be
high as in
your example. Drive is easy by way of a direct drive PP CF
pair. I've done
it.

I'm confident you'll find if you look more closely as I & others
have,
that there's no practical pwr advantage of AB2 over AB1 with
small
pentodes & even somewhat of a loss.

(John's long and excellent hands-on research post snipped)

But John, a conclusion to your efforts is omitted.

But what conclusion is necessary? I simply explained my point. As
above, here is what I had originally said in this thread-

---------------------------------------------------------
------------------------

You can get a lot of power from PP 6V6's running AB2 at reasonable
voltages. Even better, the Rla-a load doesn't & shouldn't be high as
in
your example. Drive is easy by way of a direct drive PP CF pair. I've
done it.

But don't try to run them CW. That might cause meltdown!

--------------------------------------------------------
---------------------------


Do you disagree that the same 22w in AB1 is attainable and easier
(and
done every day as well)?

There are many roads to Rome. I stated another possible hookup that
avoids high voltages. It also has the very important advantage of
using an OPT of lower impedance. That also is an important design
consideration since it is easier to get bandwidth at lower
impedance's.

ISTM (so far at least) that you've done an excellent of
demonstrating
it by proving the other side of he case.

Which other side? There are many more than just two possibilities
here. It can be demonstrated that each will have some design and/or
cost advantage.

Yes, we also have many examples of the tube as a PP class B
modulator
(WW2 light aircraft gear comes first to mind & I have run such a rig

here myself for fun). I fail to see a direct relevance of this to
the
subject, though.

Better look back at your previous post. My points in respect to your
last remark were in response to those. Here it is-

--------------------------------------------------
--------------------------------------------

Unsure what you mean by CW - if you mean RF CW, that's often a lower
level of service than a typical AF pwr stage may be due to key-up
time.
The 6V6 has also been used very reliably but at modest power as a
small PP Class B modulator. I have an early WW2 aircraft xtmr (also
in
use since 1939) that uses 6V6's in both of these ways, for either CW
or
AM phone, so all of these are very old ideas proven commercially
when
the tube was a brand new product originally designed for low drain
performance in battery powered radio gear.

--------------------------------------------
-----------------------------------------------------


Anyway, here is more data for the faithful (and others) to ponder!

6V6GT's PP into 4.2K

Power Watts THD %

5 0.57
9 Enters Class AB2
10 0.75
15 1.90
20 2.50

The same amplifier into 8.2K

5 0.51
10 0.54
15 0.65
20 Not possible

The amplifier has not been optimized at all. The THD measurements were
made using an HP 334A Analyzer. The signal source is an HP 200CD.

If you look carefully at the trace of control grid voltage I posted a
few days ago you can see a break or discontinuity where grid current
starts to flow.

Another important point to keep in mind so far as using a CF driver is
concerned is that it provides a much lower impedance source with which
to drive the following grid than the same tube as a plate connected
driver. In this example, when driving 10 ma into the 6V6GT grid one
each half of the 6BQ7 has a G of about 7 ma/volt. As a source that
translates to of about 150R, much better than you can do with a plate
driven driver. Furthermore, it can run from DC to several hundred khz,
not possible at all with an IT.

Something to think about!!

Cheers, John Stewart

Mesa Boogie make 6v6 guitar amps with 21 watts class AB1, but with
screen and plate supplies at +450v.
I am not sure what the load is but surely it is higher than 4.2k.
The latest 6v6 allow the higher Eg2, hence Eg1 bias is greater,
hence g1 swing can be higher without going into grid current regions.

The same power can easily be had from a pair of 6L6 operating in very
conservative
and easy class A conditions with lower load value, Ea and Eg2 at 350v,
and all class A.

Using the same 450v supplies with 6L6, maybe 40 watts is easy to get,
AB1.

Patrick Turner.

On Mon, 27 Jun 2005 20:20:58 -0400, John Stewart
wrote:

Makes ya wonder how much output ya could get with 1000
volts plate supply to a pair of 6BQ5's.

I wouldn't be wondering this at all, since 1,000v plate supply is a bit over
the top
and I wouldn't do it.

I would be concerned about the 9-pin socket. What about flashover? Any kind of
grunge on the socket would cause fireworks.
The OPT too. The peak voltages at max signal level will be about 1.8X the
supply.

Sorry; it was meant to be humorous. Must be a time-of-day
thingy.

Thanks,

Chris Hornbeck
"I can build you a test that will show either one. Which
would you prefer me to demonstrate?"
--scott

John Stewart wrote:

Patrick Turner wrote:

Chris Hornbeck wrote:

On Sat, 25 Jun 2005 07:08:32 GMT, Patrick Turner
wrote:

Musical Reference amps using a 700v anode supply
350v screen supply, and a pair of 6BQ5 manage 36 watts in AB1.
And this was a low thd hi-fi amp.

RLa-a is 14k.

Makes ya wonder how much output ya could get with 1000
volts plate supply to a pair of 6BQ5's.

I wouldn't be wondering this at all, since 1,000v plate supply is a bit over
the top
and I wouldn't do it.

I would be concerned about the 9-pin socket. What about flashover? Any kind of
grunge on the socket would cause fireworks.
The OPT too. The peak voltages at max signal level will be about 1.8X the
supply.

But they did make amps using EL34 and KT88 with 800v supplies.
The TT21 which is a KT88 with a top cap was a great tube to use
for a high voltage class AB amp and it'd put out 140 watts class AB2.

I built an amp using four of 6CD6GA's in PPP with 980 volts on the plates about
45 years ago. It managed an easy 120 watts. But not really safe for your living
room!!

No more unsafe than any SET amp using 1,200v.

If enclosed, HV is OK.

One dude I know had a 1960s Lennard amp with 8 x EL34,
Ea = 900v, Eg2 = 450v, and it measured at 500 watts.
It had 4 inputs and 4 sets of tone controls to allow a band
to use just one amp as they travelled around.

The amp was in a fragile particleboard case that had support legs that screwed into
it,
and was covererd in the same silvery cloth popular for suits worn by rock stars
of the era.

Most of these amps crumpled to an expensive splintered mess when they fell off a
stage,
and all had troubles with arcing between pin 3 and 2.

Patrick Turner.





Cheers, John Stewart

wrote:

Unsure what you mean by CW - if you mean RF CW, that's often a lower
level of service than a typical AF pwr stage may be due to key-up time.

In general, most tube RF CW transmitters will be rated for a 50% duty
cycle.
So they are expected to rest half the time, pulling only idle
current...

The 6V6 has also been used very reliably but at modest power as a
small PP Class B modulator. I have an early WW2 aircraft xtmr (also in
use since 1939) that uses 6V6's in both of these ways, for either CW or
AM phone, so all of these are very old ideas proven commercially when
the tube was a brand new product originally designed for low drain
performance in battery powered radio gear.

Hummmm. I never considered the 6v6 that much of a low drain tube...
When I think of those, I think of the usual 1 volters you see in old
zenith transoceanics, etc...

I did an amp with some low drain tubes a few years ago. In my case the
tubes were of the 2 volt family. The output is PP 33's which could be
connected UL or Triode.
The driver is a triode connected 33 running thru an IT which Hammond made
up for me. To get some voltage gain at the front end I used a 1B5/25S
triode which I found to be quite microphonic.

The amp manages about 2.5 watts while triode connected & about 4.5 watts in
UL mode. There is no NFB at all.

You can read about it in the Glass Audio Projects book.

See
http://www.audioxpress.com/bksprods/books/bkaa62.htm

Cheers, John Stewart

John Stewart wrote:

But what conclusion is necessary? I simply explained my point. As above, here is
what I had originally said in this thread-

----------------------------------------------------------------------------------

You can get a lot of power from PP 6V6's running AB2 at reasonable
voltages.

The devil is in the details; "a lot of power" and "reasonable voltages"
mean different things to different people. Perhaps it'd be better to
define them, and in the case of the latter, why a particular Eo is
unreasonable.

Do you disagree that the same 22w in AB1 is attainable and easier (and
done every day as well)?

There are many roads to Rome. I stated another possible hookup that avoids high
voltages. It also has the very important advantage of using an OPT of lower
impedance. That also is an important design consideration since it is easier to get
bandwidth at lower impedance's.

I see. One might well even add related advantages of CF drive over
typical AB1 voltage coupled (caps) drive, too. But what about the
6V6's G1 standing up to pwr dissipation (ignoring for the present a
tougher new version such as the JJ)?

ISTM (so far at least) that you've done an excellent of demonstrating
it by proving the other side of he case.

Which other side? There are many more than just two possibilities here. It can be
demonstrated that each will have some design and/or cost advantage.

This sounds better. :-)

Yes, we also have many examples of the tube as a PP class B modulator
(WW2 light aircraft gear comes first to mind & I have run such a rig
here myself for fun). I fail to see a direct relevance of this to the
subject, though.

Better look back at your previous post.snip

Perhaps this side comment was a distraction on my part by being taken
for more significance than it demonstrates; FWIW the modulator
application I referred to modulates a 7w carrier; only 3-4w is required
& the ckt goal was simplicity & robustness, not high(er) power output.

Anyway, here is more data for the faithful (and others) to ponder!

6V6GT's PP into 4.2K

Power Watts THD %

5 0.57
9 Enters Class AB2
10 0.75
15 1.90
20 2.50

The same amplifier into 8.2K

5 0.51
10 0.54
15 0.65
20 Not possible

The amplifier has not been optimized at all. The THD measurements were made using an
HP 334A Analyzer. The signal source is an HP 200CD.

Can you qualify what freqs (or rolloffs) - or generally is this
throughout the typical audio range? FWIW one can get over 30w that
looks quite clean on a trace @1khz with 8k iron in AB1.

If you look carefully at the trace of control grid voltage I posted a few days ago
you can see a break or discontinuity where grid current starts to flow.

Another important point to keep in mind so far as using a CF driver is concerned is
that it provides a much lower impedance source with which to drive the following
grid than the same tube as a plate connected driver. In this example, when driving
10 ma into the 6V6GT grid one each half of the 6BQ7 has a G of about 7 ma/volt. As a
source that translates to of about 150R, much better than you can do with a plate
driven driver. Furthermore, it can run from DC to several hundred khz, not possible
at all with an IT.

Something to think about!!

Suggest see how it may look to you at a load of 6.6k. Not only is this
a near-even compromise btw the other 2 which you've iterated in terms
of bandwidth-friendliness, but it's the most common load used for
high-output AB1, albeit in non-audiophile applications. This may or
may not reveal a little more.

Patrick Turner wrote:

Mesa Boogie make 6v6 guitar amps with 21 watts class AB1, but with
screen and plate supplies at +450v.
I am not sure what the load is but surely it is higher than 4.2k.

6.6k is typical of guitar amps running PP 6V6 @20+w, of which there
have been many, sheesh.

The latest 6v6 allow the higher Eg2, hence Eg1 bias is greater,
hence g1 swing can be higher without going into grid current regions.

6V6 has been run at that same "higher Eg2" for almost 50 yrs with
various degrees of reliability, it is nothing new. It is the higher
practical g2 dissipation (discovered, not rated) some newer tubes are
happy with that is significant (JJ's).

The same power can easily be had from a pair of 6L6 operating in very
conservative
and easy class A conditions with lower load value, Ea and Eg2 at 350v,
and all class A.

Which keeps bringing it back to, what is the point of pushing PP 6V6's
to higher pwr in audiophile service - or for that matter, to the same
or similar max pwr available from AB1 by driving them AB2 at lower TDH
& subjecting them to G1 dissipation, when other tubes of comparable
price do the job more suitably with simpler topology (no need for a
current-capable bias supply, for openers) & longer life?

I could see some potential value in all this if were were discussing
guitar amps - where a tube is used as part of a creative instrument
rather than an accurate reproducer and one type may respond markedly
differently from another. Last time I looked this wasn't AGA, and
perhpas it is better we stop bringing up guitar amps and speech
modulators entirely if a worthwhile mission is to be the focus of
running 6V6's in AB2 on its merit (if any) for music reproduction.

wrote:

Patrick Turner wrote:

Mesa Boogie make 6v6 guitar amps with 21 watts class AB1, but with
screen and plate supplies at +450v.
I am not sure what the load is but surely it is higher than 4.2k.

6.6k is typical of guitar amps running PP 6V6 @20+w, of which there
have been many, sheesh.

The latest 6v6 allow the higher Eg2, hence Eg1 bias is greater,
hence g1 swing can be higher without going into grid current regions.

6V6 has been run at that same "higher Eg2" for almost 50 yrs with
various degrees of reliability, it is nothing new. It is the higher
practical g2 dissipation (discovered, not rated) some newer tubes are
happy with that is significant (JJ's).

The same power can easily be had from a pair of 6L6 operating in very
conservative
and easy class A conditions with lower load value, Ea and Eg2 at 350v,
and all class A.

Which keeps bringing it back to, what is the point of pushing PP 6V6's
to higher pwr in audiophile service - or for that matter, to the same
or similar max pwr available from AB1 by driving them AB2 at lower TDH
& subjecting them to G1 dissipation, when other tubes of comparable
price do the job more suitably with simpler topology (no need for a
current-capable bias supply, for openers) & longer life?

6L6 for hifi make more sense than 6V6, definately.



I could see some potential value in all this if were were discussing
guitar amps - where a tube is used as part of a creative instrument
rather than an accurate reproducer and one type may respond markedly
differently from another. Last time I looked this wasn't AGA, and
perhpas it is better we stop bringing up guitar amps and speech
modulators entirely if a worthwhile mission is to be the focus of
running 6V6's in AB2 on its merit (if any) for music reproduction.

Musos can't really be told what to prefer, and just why they prefer
6V6 in guitar amps is a mystery to those of us who don't play
much music.


rec.audio.tubes covers all tube use, and discussions commonly
take in guitar amp practice and hi-fi.
Most diy ppl building an amp for hi-fi would
go for 6L6 in lieu of 6V6, since the cost difference is negligible, except
to the miserly types who'd whinge all day and night about the extra
$5 for a 6L6 instead of a 6V6.
Let the *******s whinge.
I prefer 6550 or KT90.

Patrick Turner.

wrote:

John Stewart wrote:

But what conclusion is necessary? I simply explained my point. As above, here is
what I had originally said in this thread-

----------------------------------------------------------------------------------

You can get a lot of power from PP 6V6's running AB2 at reasonable
voltages.

The devil is in the details; "a lot of power" and "reasonable voltages"
mean different things to different people. Perhaps it'd be better to
define them, and in the case of the latter, why a particular Eo is
unreasonable.

Do you disagree that the same 22w in AB1 is attainable and easier (and
done every day as well)?

There are many roads to Rome. I stated another possible hookup that avoids high
voltages. It also has the very important advantage of using an OPT of lower
impedance. That also is an important design consideration since it is easier to get
bandwidth at lower impedance's.

I see. One might well even add related advantages of CF drive over
typical AB1 voltage coupled (caps) drive, too. But what about the
6V6's G1 standing up to pwr dissipation (ignoring for the present a
tougher new version such as the JJ)?

Did you not carefully read the results on my tests of just that? In the example I gave, at
full output in AB2 each G1 of the 6V6GT dissipate only 26 milliwatts.
Do you consider that to be too much? If so, state your reasons. Be objective & specific in
your response. Did you ever see a spec for G1 dissipation for the 6V6 family?

You might want to look up specs for the 6F6 family. They give operating conditions for PP
Class A & AB2, for both triode & pentode operation.

ISTM (so far at least) that you've done an excellent of demonstrating
it by proving the other side of he case.

Which other side? There are many more than just two possibilities here. It can be
demonstrated that each will have some design and/or cost advantage.

This sounds better. :-)

Yes, we also have many examples of the tube as a PP class B modulator
(WW2 light aircraft gear comes first to mind & I have run such a rig
here myself for fun). I fail to see a direct relevance of this to the
subject, though.

Better look back at your previous post.snip

Perhaps this side comment was a distraction on my part by being taken
for more significance than it demonstrates; FWIW the modulator
application I referred to modulates a 7w carrier; only 3-4w is required
& the ckt goal was simplicity & robustness, not high(er) power output.

Anyway, here is more data for the faithful (and others) to ponder!

6V6GT's PP into 4.2K

Power Watts THD %

5 0.57
9 Enters Class AB2
10 0.75
15 1.90
20 2.50

The same amplifier into 8.2K

5 0.51
10 0.54
15 0.65
20 Not possible

The amplifier has not been optimized at all. The THD measurements were made using an
HP 334A Analyzer. The signal source is an HP 200CD.

Can you qualify what freqs (or rolloffs) - or generally is this
throughout the typical audio range? FWIW one can get over 30w that
looks quite clean on a trace @1khz with 8k iron in AB1.

If you look carefully at the trace of control grid voltage I posted a few days ago
you can see a break or discontinuity where grid current starts to flow.

Another important point to keep in mind so far as using a CF driver is concerned is
that it provides a much lower impedance source with which to drive the following
grid than the same tube as a plate connected driver. In this example, when driving
10 ma into the 6V6GT grid one each half of the 6BQ7 has a G of about 7 ma/volt. As a
source that translates to of about 150R, much better than you can do with a plate
driven driver. Furthermore, it can run from DC to several hundred khz, not possible
at all with an IT.

Something to think about!!

Suggest see how it may look to you at a load of 6.6k. Not only is this
a near-even compromise btw the other 2 which you've iterated in terms
of bandwidth-friendliness, but it's the most common load used for
high-output AB1, albeit in non-audiophile applications. This may or
may not reveal a little more.

I have to say that I'm not sure what you are driving at. Some of us have simply stated
certain circuit properties. Those are not about to change, no matter how much discussion.

As usual I am very busy as are others here. I will leave it to you to pick up a soldering
iron to do the further investigation. That way you can join us in contributing some sweat
to the subject.

Cheers, John Stewart