Valve amps and power ratings

[cafe67]

Hopefully not starting a fatwa , but what is it with valve amps and power ratings? 

 

I recently read a review of a integrated el34 amp officially rated at 35w per channel , but measured at 1% distortion Max power was 7w, allowing for 3% distortion got 28w close but still off. 

 

I've seen this on a few other valve amps cheap and not so cheap where the official power rating isn't really anything like measured power. 

 

Poetic licence or false advertising? 

Edited September 28, 2022 by cafe67

[sir sanders zingmore]

My guess is that it comes down to what people call “valve watts”. I interpret that to mean something like if your valve amp is clipping at 3% distortion it probably still sounds pretty good (warm/lush pick your adjective). On the other hand a solid state amp at 3% distortion is probably stripping paint off the walls. 
 

(It’s still misleading though IMHO)

[Ukrop]

On 28/09/2022 at 11:54 AM, cafe67 said:

Hopefully not starting a fatwa , but what is it with valve amps and power ratings? 

 

I recently read a review of a integrated el34 amp officially rated at 35w per channel , but measured at 1% distortion Max power was 7w, allowing for 3% distortion got 28w close but still off. 

 

I've seen this on a few other valve amps cheap and not so cheap where the official power rating isn't really anything like measured power. 

 

Poetic licence or false advertising? 

You should check the modes in which the parameters are measured. For example, in capital letters it is written about the maximum output power, THD or frequency range, and in small letters it is written that THD and frequency range are measured at an output power of 1 W.

[Ihearmusic]

Always interesting to read about wattage and distortion.

In my system (300B) I listen at roughly 80dB. That is my speakers have a sensitivity of 99dB and my amp will output around 3/4 of a Watt as measured with an oscilloscope. Distortion is around 0.3% measured with a Tektronix analyser.

So I wont get anywhere near does figures you quoted for the el34 tube amp.

These measurements are probably done into a resistive load and god knows what the objective was. Was the max Wattage at the onset of clipping? Who knows!

That is why I don't give to much attention to measurements.

Enjoy the music.........

 

[stereo coffee]

On 28/09/2022 at 9:54 PM, cafe67 said:

Hopefully not starting a fatwa , but what is it with valve amps and power ratings? 

 

I recently read a review of a integrated el34 amp officially rated at 35w per channel , but measured at 1% distortion Max power was 7w, allowing for 3% distortion got 28w close but still off. 

 

I've seen this on a few other valve amps cheap and not so cheap where the official power rating isn't really anything like measured power. 

 

Poetic licence or false advertising? 

Valve amps are simply more efficient with higher impedance loudspeakers, its explained below

http://education.lenardaudio.com/en/14_valve_amps_7.html

 

Accordingly its best to use loudspeakers rated at 8 ohms or higher. The famous LS3/5a speaker some variations of it as  I recall were 15 ohms making them an ideal companion with a valve amp.  Monacor also make a twin coil bass driver that is close to 15 ohms

 

Valve amp       power is directly proportional to speaker Impedance
      therefore   power increases as the speaker Impedance rises.
 

Solid-state     power is inversely proportional to speaker Impedance
      therefore  power decreases as the speaker Impedance rises.

 

 

 

 

Edited October 3, 2022 by stereo coffee

[RoHo]

The problem, to a certain extent, is that manufacturers are slave to the general publics obsession with certain specifications and who regard the spec as a marker of how "good" a product is.  So an amp that is rated at 100W is obviously twice as good as a 50W amp and a 20W amp is just bottom of the barrel.   The manufacturer can explain all they like about how the speaker-amp combo is what is important but the public just see "20 watts".  So they quote a power output that can only be produced "downhill with a tailwind".

It's the same with speaker efficiency.  No-one dares quote the efficiency of their small 2-way as 83-85 dB so they fudge it and quote 87-88 dB.