tube amp power vs power tube composition?

[TTA]

Help me understand, realizing i am just a bass player and have not much thought of this before.

yba100 - 6l6 x4 = 100w
yba300 - 6l6 x12 = 300w

makes sense to me.
now…

yba200 - kt88 x4 = 200w
svt classic - 6550x6 =300w
reeves custom 225 - kt88 x4 = 225w
reeves custom 400 - kt88 x6 = 400w

so i am guessing power is not just about the power tubes. what am i missing?

 

[agedhorse]

Help me understand, realizing i am just a bass player and have not much thought of this before.

yba100 - 6l6 x4 = 100w
yba300 - 6l6 x12 = 300w

makes sense to me.
now…

yba200 - kt88 x4 = 200w
svt classic - 6550x6 =300w
reeves custom 225 - kt88 x4 = 225w
reeves custom 400 - kt88 x6 = 400w

so i am guessing power is not just about the power tubes. what am i missing?

Different amp designs, different designer intent or preferences.

 

[ajkula66]

so i am guessing power is not just about the power tubes. what am i missing?

It comes down to the circuit design. Consider this:

A '65 blackface Twin Reverb was rated at 85W.

The final late '70s silverface units were rated at 135W.

All of them used a quartet of 6L6GC tubes. The changes in the circuit design that have taken place over the years resulted in larger power as well as in different sound.

 

[agedhorse]

It's not just power, it's clipping character, dynamics, damping, feel, etc.

 

[Fender_Bender]

Tubes can be stressed harder or softer depending on how much distortion and clipping is held to be acceptable. You can get away with much higher audible sound issues from driving them hard in a bass amp than you can in a high end audiophile tube amp.

 

[gtirard]

I understand we have important variations of power for the same tube configuration, depending on many factors, but I have the feeling that some types of tubes deliver more power than others, all other things being equal?
6550 and kt88 seem to deliver more power per tube than 6l6?

 

[Wasnex]

How much horsepower does a 4 liter motor make. The answer is it depends on the design. Some make more horsepower and some make less.

The same goes for tubes. The type and number of tubes does not tell you how much power the amp can make. It depends on lots of different design choices.

 

[Wasnex]

I understand we have important variations of power for the same tube configuration, depending on many factors, but I have the feeling that some types of tubes deliver more power than others, all other things being equal?
6550 and kt88 seem to deliver more power per tube thab 6l6?

Can 6550 or KT88 make more power than 6L6? I believe the answer is yes.

Does replacing 6L6 with 6550 or KT88 guarantee an amp will be able to make more power? Pretty sure the answer is no.

In some instance swapping in a higher capacity tube does bump power a bit, but AFAIK the most you will gain is probably something like 20%. Maybe an amp would make about 180W with a sextet of 6L6GC and 230W with a sextet 6550. That's a ~1dB bump in power, which is not very much.

These were claimed power figures I found for the old Mesa 400. AFAIK the 400 output section was actually designed around 6550, and a decision was made to use 6L6 because quality 6550s were not available. So in this instance, the 20% difference is probably because the circuit is optimized for 6550 rather the 6L6. If the amp had been designed/optimized for 6L6GC, the power gain from swapping in 6550 might be less, or it might even be a negative number.

Keep in mind 6550 costs about twice as much as 6L6GC.

 

[BoogieZK]

Depending on Voltages, transformers design, circuit design you can get more or less with same tubes.
Also by accepting more or less clipping you can get different power ratings.
For example the Mesa Bass 400+ is 12 x 6L6 tubes so 6 x 50W (2x6L6 tubes makes 50Wrms on datasheet normal ratings).
But i'm sure AgedHorse can explain more on this one why it's called 400+ (Standing for 400W?)

I made a 50W guitar amp with EL34 and it was monstrous because the Plate voltage was 700Vdc.
Kinda like a Hiwatt i think, they used very high voltages for more clean signal.
Correct me if i'm wrong.

Same as people are thinking tubes amps are more powerful than transistors, it's actually more a psycho-acoustic effect with clipping/distortion.

 

[sunburst79]

All things tube must pass through an output transformer. That's part of the power handling or output equation. The iron has a limit.

How much power a particular tube type can make is influenced by its available power supply. Voltage and current and filtering and rectification all play into this.

The amps designer decides if he's going to push a particular tube type to the very edge of its performance envelope or run it conservatively.

So power output is more than plate dissipation times the number tubes.

 

[TTA]

How much horsepower does a 4 liter motor make. The answer is it depends on the design. Some make more horsepower and some make less.

The same goes for tubes. The type and number of tubes does not tell you how much power the amp can make. It depends on lots of different design choices.

i understand that 100%.

so if you have say a reeves kt88x6 that makes 400w vs a 300w svt, what kind of changes/consequences might we expect to see?

edit: from other replies i gather we might see higher voltages, bigger transformers, more clipping characteristics, and i presume more stressed power tubes?

i will do some research on tge hiwatt design also

thanks to all

 

[agedhorse]

I understand we have important variations of power for the same tube configuration, depending on many factors, but I have the feeling that some types of tubes deliver more power than others, all other things being equal?
6550 and kt88 seem to deliver more power per tube than 6l6?

The 6550 and KT88 are much bigger tubes… they can operate at higher voltages, currents and plate dissipation than a 6L6.

i understand that 100%.

so if you have say a reeves kt88x6 that makes 400w vs a 300w svt, what kind of changes/consequences might we expect to see?

edit: from other replies i gather we might see higher voltages, bigger transformers, more clipping characteristics, and i presume more stressed power tubes?

i will do some research on tge hiwatt design also

thanks to all

Its everything.

More voltage, more current, higher plate dissipation limits, more screen capacity, lower transformer ratios, better matching to the load, etc.

I see repeatedly comments about the size of the transformer… "big iron". In reality, it has nothing to do with the size but with the efficiency. A more efficient transformer can be built smaller if the laminations are from higher grades of magnetic steel. While more expensive, being smaller requires less copper because the winding length is shorter, this reduces losses too.

 

[Wasnex]

from other replies i gather we might see higher voltages, bigger transformers, more clipping characteristics, and i presume more stressed power tubes?

Yep

 

[Wasnex]

so if you have say a reeves kt88x6 that makes 400w vs a 300w svt, what kind of changes/consequences might we expect to see?

The operating voltages are fairly similar for both amps during idle. Both run the plates around 700V. Modern SVTs run the screens around 350V. The Reeve may run the screens around 400V. I believe the Reeves has higher capacity transformers. AFAIK this means the operating voltages will sag less as the amp is asked to make more power. .

I own a Reeves 400 as well as 69 and 87 Ampeg SVTs.

The Reeves is louder than the 87. I am not certain it's louder than the 69.

My Reeves 400 has eaten quite a few KT88s.

The original SVTs ran 6146 tubes. I have seen claims that SVTs running 6146 can make about 450W relatively clean...even though they were rated for 300W. However, I believe 6146 is less resilient than 6550 when pushed into drive territory. The early amps had reliability problems when pushed hard, and the design was changed a bit. I believe SVT production changed to 6550 in mid 70.

 

[bassbrad]

Also there is no agreed upon criteria for measuring and specifying power output, it will depend on the designer and marketing departments so it is nearly impossible to do an apples to apples comparison.

 

[darwin-bass]

And yet, going back to my ham radio days, transmit power was pretty much determined by the type and quantity of output tubes. I'm pretty sure the power amp sections of shortwave transmitters were all pretty much the same class / topology though, and the output purity was governed by FCC regs. So totally different world.

 

[agedhorse]

And yet, going back to my ham radio days, transmit power was pretty much determined by the type and quantity of output tubes. I'm pretty sure the power amp sections of shortwave transmitters were all pretty much the same class / topology though, and the output purity was governed by FCC regs. So totally different world.

Depending on the transmitter, the tubes were operated non-linearly too. Still depended on the external circuitry and design choices though.

 

[TheArchitect]

Help me understand, realizing i am just a bass player and have not much thought of this before.

yba100 - 6l6 x4 = 100w
yba300 - 6l6 x12 = 300w

makes sense to me.
now…

yba200 - kt88 x4 = 200w
svt classic - 6550x6 =300w
reeves custom 225 - kt88 x4 = 225w
reeves custom 400 - kt88 x6 = 400w

so i am guessing power is not just about the power tubes. what am i missing?

Different tube types produce different levels of power. 6550 and KT88 produce a lot more per tube than a 6L6 or EL34

 

[agedhorse]

Different tube types produce different levels of power. 6550 and KT88 produce a lot more per tube than a 6L6 or EL34

IF that's how the circuit is designs. In the wrong circuits, it's possible for those tubes to produce less power too.

 

[skier 913]

IF that's how the circuit is designs. In the wrong circuits, it's possible for those tubes to produce less power too.

If an amp with 6l6's says it can take EL34's, does that mean that it can also take 6550's ?