Amp power and tube number?

[Homebelly]

Not sure if i'm in the right forum for this question..

How does the number of tubes in an amp relate to the amps out put rating?
And what role does the out put transformer play in the equation?

Reason i'm asking is, i am about to dive into my first JTM45 kit.
I'm no stranger to tube amps, been playing through them for years, and so this is a question that has been lingering for a while now. I've played through and owned many great amps including soldano's Marshalls fenders and vox's. I currently own a Matamp 1224 MKVI. To use the Matamp 1224 as an example, this is rated at 40 watts, and has 4 EL34's in it. An AC30 also has 4 EL34's and produces 40 watts, yet a marshall 50 watt plexi is only running 3 out put tubes, as is the 30 watt JTM45.

Can any one give me the skinny on this?

Cheers...

[mathd]

The plexis is 2 output tubes as the jtm45
They are rated at 30-50 watt BUT when dimmed/overdriven they reach higher wattage then this...(about 80 watt for a 50 watt head and 180 watt for a 100 watt head)

Now to the wattage difference.
First there is EL34 and EL84 tubes.
The EL34 is almost just like a kt66(technically speaking) and other tube of its categorie, it is a 25 watt tube. The EL84 is a much lower wattage output tube.
There is also class A and Class AB(Push Pull) power amp. This will make a hudge difference in output wattage and also in tone.

So far that is what i know.

[neikeel]

An amplifiers output is related to the type of output valves, the way that the valve output stage is configured, the efficiency of the output transformer and the voltages that are supplied to the output transformer by the power transformer

The Matamp 1224 is powered by four 6V6 valves (like some low powered 4 pot Fenders) for 28 watts it can run EL34s or 6L6 for more output if needed, it is also a clever design as it can also be switched from pentode (full power) to triode mode for lower output.

An AC30 runs four EL84s and will typically put out 30 watts.

A 50 watt plexi uses two output valves (usually EL34s) a good one puts out 50w clean (RMS) but much higher peak power. Similarly a four EL34 powered plexi will put out up to 150 watts of distorted power. The KT66 in a JTM has less output and the amps correspondingly less output.

Suggest you get a decent basic valve amp text book to help distinguish between the way that the current flows in the diiferent stages of amplifiacation in Class A, Class B and Class AB amps as that will also vary the output significantly.

[arledgsc]

And what role does the out put transformer play in the equation?

Impedance matching. The OT transforms the high tube impedance to lower speaker impedance. Power on the both sides of the OT are the same (minus efficiencies and loss) when these impedances are matched. Different tube types due to their construction, amplification class (A, AB, B, etc), or the number of tubes in parallel effect this output impedance and may require adjustment of the OT impedance to achieve maximum power transfer to the speakers.