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

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.

Gents,
+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.