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A review from Steve Guttenberg http://www.cnet.com/news/straight-outta-texas-the-apex-teton-headphone-amplifier/
The Apex Teton is a single-ended output-transformer-less (OTL) vacuum tube preamplifier and headphone amp. Its roots lie in the Wheatfield Audio HA-2 from nearly 15 years ago. While similar, it is far superior to the original design. Retaining the same tube compliment and amplifier topology, it has been greatly improved through the use of a better power supply and higher quality components throughout.
The all-tube Teton uses a single voltage amplification stage followed by a current amplification stage. There are no transformers in the direct signal path, and only one coupling capacitor*. To provide low noise and solid bass response, the Teton uses a vacuum-tube rectifier and a multi-stage LC filter.
Like other Apex tube headphone amps, the input stage uses the venerable 6SN7 tube, often regarded as the best tube ever made for audio voltage amplification. The power stage uses a 6080 dual triode, which can optionally be replaced with a number of other power tubes like the 7236, 5998, or 6528, tailoring the sound to the owner's headphones and musical preferences. This combination, along with massive polypropylene output capacitors, gives the Teton a powerful sound along with the musicality that only a single-ended tube amp can give.
The Teton is a fully unbalanced, single-ended amplifier. The input and output selections are made via a front panel switches, which activate relays that are strategically located to keep the signal path direct and pure.
Like other Apex products, the Teton is designed and hand-built in the USA, using high quality components sourced largely from the US and Japan.
Specifications
Tube complement: Input - 6SN7. Output - 6080 standard (optionally 6AS7, 7236, 5998, or 6528). Rectifier - 5U4GB standard (many options possible, including GZ34/5AR4, GZ37, etc.)
Inputs: Three unbalanced RCA connectors
Line output: One unbalanced RCA connector
Volume control: High quality TKD potentiometer
Headphone output: 1/4" TRS unbalanced. Can drive loads from 16 ohms and up
Dimensions: 17" wide x 7" tall x 11" deep
Power: 120V or 240V, 50/60Hz
* Regardless of what some people may have you think, the power supply circuitry as well as any bypass capacitors are actually also in the AC signal path. Even though they are not as critical as components like coupling capacitors, because of this, only high-quality capacitors
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