One of a kind Single Ended 71a

At .75 watts (or 750 milliwatts!) of power, the archaic 71a is about as low power as it goes in hifi, and represents the outer fringes of single ended amplification. The only power tubes with similar low output that I know of would be the 1626, made famous in the "Darling" circuit.

This is the ugliest amplifier that I have owned, but one of the best sounding within its limitations, and overall is one of my top 3 favorite amplifiers so far and one of the few I have really regretted letting go. When I owned it, this is the one that was running more than half the time in my rig. The bass is not going to rock the neighbors here, even on super efficient speakers, but the tone and warmth is superb and much like its bigger brother the 45, but with a slight bit of something added that makes it more smooth, maybe a bit more rounded. It takes quite a while to warm up and arrive at its sweet spot, sounding best after being on for an hour or more. The details and nuances presented here are difficult to appreciate during the daytime when there is so much ambient noise, but later in the evening this is the amplifier that I choose over all of the others.

This amplifier has a headphone section (maybe the only 71a headphone amp on the planet?) and also incorporates a tube regulated power supply, featuring a 6BH3 rectifier, an OD3 regulator, and a 6KD6 that is being used as a constant current draw. The output transformers are from a Zenith single ended console amplifier, likely late 50's or early 60's, and the 71a tubes are driven by a pair of ancient mesh pate 37. The 71a pictured here are early Tungsol and sound fantastic. Farther down the amp is pictured with a fine set of Arcturus tubes with the classic blue glass; a nice marketing touch from the early 1930s.

One of the best things about the 71a tubes are their prices. The fact is there is just not much demand for these tubes, unlike say its bigger brothers the 45 or 2a3. A nice testing pair of 1920's globe 71a can be had for well under $100, less than the price of a single low-end Chinese 300b. And sounding as good as it does, that makes it such a great place to be. Be warned though that these require the highest efficiency speaker to fully appreciate.

If anyone viewing this page knows who made this amplifier, please send me an email. I'd love to know more about the amp and the person who created it.

There's something about mesh tubes that are really appealing. I think it's safe to say that we'll never see modern production mesh plate 37 tubes again. These beauties date to the 1930s.

The regulated power supply is an unusual feature of this amplifier.

Several transformers or chokes are in the power supply as well.

The beautiful blue Arcturus tubes really make this amplifier look cool! One of the great pleasures of owning gear like this is the opportunity to use tubes made so long ago. My grandmother was a girl when these rolled off the line! How many electronic components being made today will still be treasured in 2090?