So just how powerful is my Trainwreck homage?

[nee]

(Can't really call her a clone!)

Greetings!

I have 2 x KT77s, plate voltage is 386V and the KT77s are drawing 42mA each, giving a static dissipation of 16.2W per tube.

How does this relate to the real-life, turn-it-up power output of the amp? Is she a 32.4W amp, or will she be putting out more power once I'm thrashing the Les Paul? And if so, how do I do a ballpark calculation of this?

Many thanks!

[Structo]

Well the max plate dissipation is 25 watts.
I'm not sure if that is at the onset of distortion or how they rate them but most likely that is the most to expect out of it before it self destructs.

But with a max plate voltage of 800v, you aren't near to design limits with that tube.
According to my calculations a 70% dissipation for that tube is around 45ma. Not counting the screen current.

Have you figured what the screens are pulling?

I think the simple way to test the amp is into a dummy load then measure the voltage across the resistor.
E2/R=P

[Alexo]

Plate dissipation, which happens to be measured in watts, doesn't really come into play for measuring output power (also measured in watts). Consider a single-ended 6V6, biased to 12 watts, only giving you 5 watts of power.

The best way to measure output power is to hook your amp up to a scope and a signal generator and measure RMS voltage just before the onset of clipping, then square the RMS voltage and divide by your load.

If you don't have the equipment above, you can just plug in your guitar and measure the voltage across your speaker terminals with your multimeter, most already measure in RMS, so just take the AC volts reading, multiply it by itself and divide by your impedance. You may see 50% or so more power under distortion than clean. If you imagine a sine wave and a square wave with the same peak level, and average the power contained in each, you can see why this is so.

[nee]

Thanks for these replies. So when a company advertises an amp as having a certain amount of power, how do they ascertain that? For example, the AC30 is said to be a "30 watt" amp; or the classic Marshal "18 watter".

Thanks!

[Cliff Schecht]

TBH, those ratings are best used to just tell you the tube type and relative volume (which is also dependent on distortion, volume, etc..). 15-18W means 6V6 or EL84 push-pull, 30W is a quartet of 84's or 6V6's, 35-50W is higher power push pull pair (6L6, EL34, etc..) and 100W is a quad output section. 3-5W is EL84 or 6V6 SE. For production amps, this all usually holds true. For homemade amps or the more experimental amps available, you just have to look at the relative plate dissipation of the power tubes and make judgments there.

Of course different speaker sizes and combos will also change how much volume your amp spits out.

[jaysg]

The marketing department employs flexible reality analysis techniques.

[Alexo]

'tis true... you can do the math on your load line and see what wattage you would get in a theory, but in reality, you have losses in the OT, power supply sag, etc., that reduce your actual output power.

IME, measuring actual power output is the best way to see what you're actually getting, and even then, all you can really do with that number is spec the minimum wattage for your speaker.

[Bob-I]

The marketing department employs flexible reality analysis techniques.

Read the specs sheet on the Peavey classic 50. They adjusted the bias to get the 50 watts out of it, then put a "kids don't do this at home" note on the page. :LOL:

I tested one awhile ago and get 36Watt from it, fuckin loud 36 watts.