Max power output for various amps?

[Regis]

Hi Guys,

Looking for maximum power output, I mean dimed and pushed hard with an overdrive, for a Bassman head, Traynor YBA1 head, and an AC30CC? Opinions?

The Bassman purportedly is 50 watts RMS, the Traynor 40 watts RMS, and the Vox about 30.

When push hard and clipped they all will put out more, wondering for attenuator purposes how much.

Thanks,

Regis

[jrfrond]

Bassman or other Fender 2- 6L6 amps are generally good for between 35-40WRMS. They call it 50, but it's not. Not if you measure it at the onset of clipping. The YBA-1 is somewhat conservatively rated at 40WRMS. It's a realistic figure, but I've seen them higher, and AC30's usually clock in between 25-30WRMS.

Using a scope and a True-RMS meter is close enough, but to be really accurate, you need a distortion analyzer or even better, an Audio Precision to get the REAL figure, before the onset of distortion.

Any amp will only put out as much power as is determined by the B+ voltage and power tubes. After that, there is no more wattage available, but power compression can give the illusion of increased loudness.

[Regis]

Yes, John, but isn't the RMS rating before clipping? And doesn't the amp exceed that RMS power when driven into distortion? That's the figure I'm looking for. It doesn't have to be precise, just in the ball park. I'm trying to figure out how much actual power is being fed to my diy attenuators.

Thanks
Regis

[pdf64]

Welcome back!
The rule of thumb, ruling out power supply sag, unmatched tubes etc, is that the max overdriven power (ie squarewave) is 1.414 x the max clean power.
I'd expect the attenuator to be rated 'for a 50 watt amp' or whatever, in the knowledge that the amp would be overdriven.
If it's your DIY unit, best practice is not to drive resistors continuously at higher than 1/2 their rated power.
So adding the above, a 50 watt amp would put out nearly 75 watts so the attenuator should be rated for 150 watts. Pete.

[Jazz P Bass]

I just repaired a Traynor YBA1 head,
The original output transformer was toast.
I measured the output at 50 watts max.
Yeah a Fender Bassman will do 40 -45 watts easy.

[Enzo]

John, his premise was not pure ratings, he indeed wants to know what happens AFTEr th onset of clipping.

My thought is that if your load needs to soak up 50 watts, more or less, then wondering if your amp puts out 45 or 55 is irrelevant. You should be designing the attenuator to handle at least 100 watts safely to start with. And yeah, 150 watts even better.

[Tom Phillips]

I agree that good practice is to design for 2X the True RMS clean power output.

I offer the following information from my notes of actual Bassman power output measuremetns.
All measurements were taken using a resistive load to match the designed output impedance and a true RMS voltmeter. Clean is my call evaluating the output waveform scope trace as a subjectively undistorted waveform. "Full clipped" is pretty much a square wave output with whatever drive it took until the output power measured would go no higher.

Results vary quite a bit from model to model and from amp to amp within the same model type.
Model 5F6A Bassmans varied from 31W clean / 45 W Clipped to 45W clean / 72 W Clipped
Model 6G6 Bassmans were usually right around 50 W clean (I have notes of one at 49W & one at 52W but for some reason didn't record clipped.
Blackface Bassmans varied from 32 to 48W clean and then all topped out at 50 to 51W full clipped
The Bassman 135 ranged from 84W clean to 145W clipped.

Anyway, there is some data that doesn't change the previous discussion much but that I thought would be interesting. My experience is that the beefier amps exhibit a larger difference between the clean and full clipped power output. JCM 800 series and earlier Marshalls come particularly to mind.

Regards,
Tom

[Regis]

Thanks for the information fella's, that helps!!