Why does my 35 watt tube amp draw 300 watts of power


I have a Prima Luna Prologue 1 (tube amp). Love it.

Always been curious though. It draws 300 watts of power, yet is rated at 35 watts / channel. Is it really so inefficient that it is losing 230 watts to heat?

79ee45c9 73de 479a 9f6b ab4f75b05b18jimspov
In a word: Yes.

Hi Jimspov,
I have an 8 watt SET amplifier  (class A ) that draws 180 watts. The sound quality is sublime and it is the best sounding amplifier I've owned. In my opinion the inefficiency is a small concession for consistently wonderful listening sessions. The bottom line is that you love the sound of your amplifier and that's a good thing. 
That's basically it.

At the other end of the power consumption spectrum I have 500 w/ch Class D Bel CAnto ref1000m amps that draw 5 watts/ch idle.

Class D technology is a game changer.    If not for having discovered success trying Class D,   I might well be down a totally different path than I am these days.

Tube amps are only 5% efficient. If you want efficiency, the class D amps are the most efficient. 
If efficiency is the objective then without question class D wins vs tubes, no argument. If class D suits your sonic and musical needs then you have achieved the best of both worlds ànd sincere congratulations. Thus far in my experience class A simple low power tube amplifiers push my buttons.  Good luck to all in their search for genuine satisfaction wherever it may lead you. 
I have a Prima Luna Prologue 1 (tube amp). Love it.

Always been curious though. It draws 300 watts of power, yet is rated at 35 watts / channel. Is it really so inefficient that it is losing 230 watts to heat?



Heater current. Volts X amps = watts.

The way I look at it these days, Class A (many tube or some SS amps, very inefficient) or Class D are the two pure approaches to consider at each end of the power consumption spectrum.   Then there is Class A/B which most SS amps are, that prior to Class D was teh technology used to improve power consumption and retain "quality sound"   Some will argue Class A/B is a compromise approach  ( I might tend to agree) that might still yield very good results but not as easily or as often as Class A.

IMHO, in general, these days, I would rather go with either Class A or Class D amps for pure sound quality.  Either done well and matched to the right gear can deliver top notch performance, subject still to personal tastes as always. 

Class D is fairly mature these days and offers a nice bundle of value and performance in a small package that will appeal to many. 

Class A amps, will tend to be larger and cost more to operate but some may still see the value if its "that sound" they like and cannot find elsewhere.

Well said and summarized. Choice is indeed a beautiful thing. 
The short answer to your question is "yes."
Tube amps are only 5% efficient.
We can easily see from the opening post of this thread that the above statement is false. If you can get two channels of 35 watts from 300 watts of wall power, clearly the amp must be more like 20% efficient, in this case 23.33% efficient, which falls within the norm for many tube amps.
+1 to the cats that chimed in above, they have it exactly right. I have heard several Class D amps in my system and found them all dry and lifeless, although the newer variants appear to be better sounding. I heard a pair of Channel Island Class D mono-blocks amps paired with VSA speakers and they were splendid, vastly better than the Class D amps I have tried in my system.  I am currently using a 10wpc Dennis Had SET amp with my Spatial Audio Holograms and the sound is warm and luscious, but I admit I prefer the sound of tubes.  Power consumption and my electricity bill is neither here nor there in my decision to use tube amplification as it turns out to be a pittance either way.   Tube amplification sounds the best to my ears.       

More than likely it only draws 300 watts at full power output. Probably a lot less at idle and playing at moderate levels.
Power efficiency (and excess heat) was a concern of mine when I ran just solid state gear, but since I became hooked on tube gear  ...well, if inefficiency is the price for this kind of a wonderful listening experience I'M ALL IN!

But, this comes at a price —not just heat but time to warm up and "disposable" tubes if you listen for hours on end and do so day-after-day. For serious listening: Tube gear. For convenience: something solid state. 
I have a Dialogue premium HP, 85-90W/channel and 540 Watts consumption (max.)  Like you said, love it, not going back to Solid State.

Cost wise, running the amp at full consumption for 2 hours each day costs $.09/day or about $3/month.  In reality probably only using 200W max, so we are talking about another $1-2 per month in expense, $5 if it runs for 4-5 hrs each day.