SE Amp - How Many Watts?

[Jag]

Using the voltages and cathode resistor values from this schematic as an example, http://www.schematicheaven.com/fende...a764_schem.pdf, how many watts do we rate the amp at.

At idle, the amp is dissipating 14.34 Watts, correct?
(342-21)*(21/470)=14.34

After reading the information at http://www.aikenamps.com/Why70percent.html, I assume that since he says dissipation in an SE amplifier is at maximum during idle and drops to about half at full output, we would rate the amp in our example at about 7 Watts. Is this correct. I've been working on tube amps for about three years now and have learned quite a bit, but I've never been sure about this issue.

Thanks,
Jag

[Chris / CMW amps]

The calculating is almost correct, you're also measuring the G2-current...

Champ with one 6V6: about 3.5 to 6 Watts depending on the B+ and used OT.

In theory (!) a single ended amp does put out 50% of the plate-power at idle but amps/circuits/OTs aren't perfect so expect about 40%.

[Jag]

Thanks Chris, that was quick.

Is there a way to calculate G2 current? (It's probably obvious and I'll kick myself for not figuring it out.)

[Chris / CMW amps]

Thanks Chris, that was quick.

Is there a way to calculate G2 current? (It's probably obvious and I'll kick myself for not figuring it out.)

After a day amp-work some surfing on the www

Measure the voltage across the 1k resistor between the OT and screengrid without the preamp-tubes installed in this case. Devide that voltage by the 1k resistance to calculate the current.

[hasserl]

Don't confuse plate dissipation with power production. Plate dissipation is of the DC current consumed; power production is of the AC produced rated at the point of clipping, not at full output.

Inject a clean signal into the front of the amp and measure the AC at the output at the point of clipping. Square the result and divide by the resistance.

[Bruce / Mission Amps]

For Jag:
Most Champ amps with stock transformers cannot pass a clean "class A" signal from the OT at more then 1.7 to 2.5 watts.
They are grossly over rated at 5-7 watts.
Even with a big aftermarket OT it is rare to see more then 5 watts in a single 6V6 amp.

[Jag]

Thanks for all the great replies. This has been very helpful and informative.

Jag