measuring output power

[amptweeker]

I have decided to go back the idea that this amp puts out about 25 watts in this example
and I have lost the drive for "accurate measurement of power.
Thanks to all for replies

[g1]

Sometimes I find that oddball amps run an impedance mismatch, perhaps for less distortion. The trade off is less power output than you would expect.

[nevetslab]

And, in spite of having all the gear needed to be clinical about it, I rarely bother measuring power output, let alone distortion. Normally, it it sounds 'nominal' lke all the others of the same model, and, if a tube amp, the plate current readings all make sense & the amp sounds good, I'm happy.

[soundmasterg]

And, in spite of having all the gear needed to be clinical about it, I rarely bother measuring power output, let alone distortion. Normally, it it sounds 'nominal' lke all the others of the same model, and, if a tube amp, the plate current readings all make sense & the amp sounds good, I'm happy.

I built a Vox AC100 clone several years ago that I added a second higher gain channel to. I haven't finished it and have to gut it and start over with a new layout to fix an issue, but when it was functioning the power output was less than the 100 watts RMS or the 80 watts RMS that Vox claimed for the fixed bias or cathode bias versions respectively. I was only getting about 65 watts RMS with fixed bias or a bit less on cathode bias with about 480V B+ and a correct impedance Heyboer OT and running into a correct resistive load. I haven't been able to get back to the amp to troubleshoot further but it would be nice for it to make the expected power. After reading this thread I realize that some of it could be because I was measuring the power with a completely clean sine wave on the scope instead of the 5% distortion as others have mentioned....but that still doesn't explain the excessively low power output. If I had a distortion analyzer that would help to get the 5% that I am supposed to have when measuring power output. After I finish some other things I hope to get back to that project and after I rebuild it with the new layout, get back to finding out why the power output is lower than expected.

Greg

[Jazz P Bass]

When faced with an output power issue I usually attempt to narrow it down by observing the input voltage to the output tubes,

As a general rule a 50 watt amp you will see a 50Vac RMS signal at the grids.
A 100 watter will need 100 Vac RMS.

[Dave H]

When faced with an output power issue I usually attempt to narrow it down by observing the input voltage to the output tubes,

As a general rule a 50 watt amp you will see a 50Vac RMS signal at the grids.
A 100 watter will need 100 Vac RMS.

Are you sure?

[nickb]

If you want to live happy donīt read your girlīs stored messages and donīt measure Tube power amps

Both so very true