Side Project: A lower-power power-amp

I'm somewhat obsessed with saving power - just ask my wife who calls me the "Heat Miser". 

So, the idea building power hungry, Class A, Single Ended tube amps seems a bit contrary to my lifestyle.  Well maybe.  My prototype 6B4G Triode based amp draws just over 40 Watts... not too bad and I'm still satisfied with that design.  But while waiting the postman to deliver a few extra supplies for that one, I prototyped a simple Single Ended amp based on a 6V6 pentode.  I chose that tube because it has a rather low heater draw for the power output it produces (2.8 Watt to heat it for up to 4 Watts of output).  I used a 6SN7 for a driver.  It's renowned for it's low distortion characteristics.  After a couple hours crunching numbers to bias the tubes, another hour to scrounge parts, another hour to build it, and 10 minutes to find one missing ground, I had a working channel.  It sounded pretty good, so I copied it to a second channel.


Now it sounded really good, especially on semi-acoustic music with nice vocals (Neko Case, Fleet Foxes, Yes, CSN, Jim White, Iron & Wine, etc.). The bass end was great.  After first spark up around 8pm, I literally listened to various tracks all evening - quite a break-in.  It was somewhat unforgiving on bad or old recordings and didn't move me so much on rock tracks, but overall it was very listenable.  Even before measuring distortion, I knew it had more 2nd order distortion than my Triode amp.  Sure nuf, it measures 6.8% THD @1kHz (-23dB 2nd order, -46 dB 3rd order).  Not super, but there's still some room for tweakin.

Here's the kicker - It draws only 22 Watts while putting out about 1.5 Watts per channel - plenty for living room levels on efficient speakers (90+ dB/m).  So for the same carbon footprint of my wife's 5 minute daily hair drying (1200 Watts), I could listen to music for 4.5 hours!  I'll let the speaker draft and tube heat dry my (orange spikey) hair.