Single-ended 2A3 Stereo Tube Amp


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When I first heard a 2A3 pass signal I was floored. There seemed to be so much missing. So much information that didn’t seem to belong was now gone. I felt as if a noisy refrigerator compressor that was running in the same room with my sound system just switched off and left me alone with the music.


It was at this point that I began to reconsider the use of nine pin tubes. They just seem so tiny and tend to go microphonic. Many worthy circuits utilize them, and they are still far better than their problematic and disposable solid state counterparts. But as far as current design efforts go, I am leaning squarely backwards to fewer pins and/or larger sockets, octals at least. Infrastructure is everything.

This circuit is a classic 6SL7 tube wired in series-regulated push-pull, driving a 2A3 directly heated triode for about 3 1/2 watts of output power per channel. The components are discreet. The topology is over the top. Turrets, no foils! That is a battle cry. I’ll shout it again: Turrets, no foils!

The same steel bar embedded in Martin’s guitar necks and what made them famous is also used in Specimen amps to support the transformers and protect against inertial impact distortion. That means that when you drop the amp, the chassis panel doesn’t bend and the transformers don’t wind up in a trapezoidal shape with stretched windings, causing hum and failure. For thirty four years people have been bringing me amps to fix, complaining of hum and failure.

Color Finishes:
The Specimen Single-ended 2A3 Stereo Tube Amplifier is made using the same Baltic Birch plywood as my horn speakers and can be finished to match perfectly. Presently I offer the following colors:

– Natural
– Dark Walnut
– Dark Green
– Dark Red
– Dark Orange
– Yellow
– Blue

*Opaque finishes are an additional $400 (e.g., black, white, or other custom opaque color)


  • Circuit

    Single-ended directly heated triode, Class A

  • Tubes

    Two 6SL7 pre-amp tubes, Two 2A3 power tubes, GZ34 Rectifier
    **Tubes Sold Separately**

  • Power

    3-1/2 watts per channel

  • Inputs

    Two RCA line-level

  • Dimensions

    16" deep x 11" wide x 8" high

  • Weight

    22 lbs.

Specimen Single-ended 2A3 Stereo Hi Fi Tube Amplifier
Specimen Single-ended 2A3 Stereo Hi Fi Tube Amplifier
Specimen Single-ended 2A3 Stereo Hi Fi Tube Amplifier
Specimen Single-ended 2A3 Stereo Hi Fi Tube Amplifier

“Having spent some time with the 2A3 the last couple weeks I have to say that I’m quite impressed.  The noise floor is non-existent, perfectly black, and it really pairs well with the horns and sub.  Nice work.”

Dean N. Fugate