Wattage how does design in power section decide this?

[James Rock]

How does amp design change wattage. I see single ended amps with the same wattage as amps with 2 or more power tubes and then amps with a quad at 30 watts or 50 watts or 100 watts. What determines this? I know class has to do with it as well as power tube type but still i see VOX AC30 (essentially class a up to a/b) and something like the bivalve which is class a and one uses four power tubes the other uses 2 yet they are the same wattage??

 

[Wattage]

Re: Wattage how does design in power section decide this?

I don't know.

 

[BigAlTheBird]

Re: Wattage how does design in power section decide this?

:haha:

 

[jeremy]

Re: Wattage how does design in power section decide this?

I don't know.

i just knew something like that was gonna be in here!!

different tubes have different potentials and running the power tubes at higher voltage will give you more power.

el84's will give you about 8w
6v6's about 12w
6l6 25-30w
el34 25-30w
6550 and kt88's can push 50w+ depending on the tube and circut. i had a 50w marshall that was running 6550's with almost 600v on the plates which was probably pushing 90w+

you can push the tubes harder than that but they tend not to sound musical and will not last long. im guessing at the wattage for the tube types but they are close

a 6l6 tube running at 350v will sound browner and have less power than the same tube running at 450v which will be louder, tighter, brighter, and more focused on the bottom end

 

[Lake Placid Blues]

Re: Wattage how does design in power section decide this?

Since you know that there's Class A and Class B, and Class A /B, you know there's quite a different range of output depending on class and other paremeters in the circut. In a Class A circut, the tube handles the entire wave form. In Class B it only handles 1/2 of the wave, and another tube handles the other 1/2. Class A/B is like class B, but with a little overlap. The range of output can be radically different, for the same exact tube, such as a 6L6, for example:

Class A triode connection (300 plate voltage)-1.8 watts
Class A two tubes pentode connection (360 plate vltage) 18 watts
Class AB1, two tubes, pentode connection ( 360 plate voltage) 25 watts
Class AB1, two tubes, triode connection (360 plate voltage) 12 watts
Class AB1, two tubes, Pentode connection (450 plate voltage) 48 watts

Another factor is the headroom provided by the power supply. A tube amp is rated at clipping, or when the amp first barely beginns to distort, not it's max output. With low head room, this might occur at 30 watts, but on a higher head room design this might occur at 50 watts, for two amps with the same tubes and actually the same potential max output of say 90 watts.

The output at clipping in the same circut may be different for different tubes. For example, the JMP era Marshall 100's, with four EL34's, typically reached clipping at about 105 watts, but reached max output with distortion at 180 watts. The same amp with 6550's would reach clipping at a much higher output, but the overall max output of the amp with distortion would still be about 180 watts.