transcription electronics
Above is the Transcription Electronics 211 power amplifier. $7999 each. 48 WPC. This power amplifier is amazing and will drive almost any speaker 211/KT77. Even with extremely efficient speakers this amp has a dead quiet noise floor. The matching 6SN7 line level pre amplifier with remote control (4 inputs, 2 RCA outputs) is $2799. Full information below…
The Transcription Electronics 211 Power Amplifier delivers performance uncommon to single ended amplifiers and represents a pragmatic approach in tube amplifier design allowing much higher power while retaining stability, low distortion, and a dead quiet noise floor.
There has been an abundance of low power directly heated SET tube amplifiers on the market since the single ended triode revival in Japan in the 1990’s. SET amps are usually built around the 2A3, 300B, #45, and 845 tubes which are convenient as the design process mostly revolves around getting enough voltage into the control grid to obtain maximum power, selecting an appropriate operation point, and implementing a suitable output transformer. For a tube like the 2A3 even some of the lowest performance output transformers can provide compelling performance. The downside to these designs is a lack of available output power, or in the case of the 845, a very high operating voltage and an output transformer that’s complicated to design and difficult to manufacture.
The output of these SET amps was typically limited to a maximum of around 25W. The first method of increasing the power output involved designing a driver which could push the grid of the output tube to positive grid voltages. This is difficult to do, as the impedance of the output valve grid will transition from several hundreds of thousands of ohms down to several hundred ohms, and the driver stage has to cope with this. Initial designs focused on interstage step-down transformers to accomplish this goal, but these were costly, still had substantial output impedance, and restricted bandwidth. These issues were overcome by Hirokuni Michimori in the early 2000s with his regulator tube drive method. Michimori used a high GM triode as a direct coupled cathode follower to push past the typical limitations in single ended driver circuits, albeit with some added complexity.
The second method to increase power in a single ended amplifier is to use much larger output tubes. Unfortunately most of these large output tubes prioritized amplification factor (mu) over low plate impedance (rp), so while it might be possible on paper to make a zero-feedback high power SET amp, you might end up needing an output transformer that’s impossible to wind or incredibly high plate voltages that are unsafe and difficult to work with. In Michimori’s amplifiers, the struggle of the impossible output transformer was resolved by applying global negative feedback and cathode feedback. Cathode feedback requires proprietary output transformer designs, while global feedback creates an amplifier that isn’t particularly stable, as well as manifesting qualitative issues with sound reproduction.
What worked for Western Electric 90 years ago to tame a 6L6 tube is equally applicable today to higher mu transmitting triodes. By combining this method with Michimori’s tube regulator drive allows the Transcription Electronics 211 amplifier design. The directly coupled tube regulator drive allows running the 211 at a low voltage (750V) while still obtaining stellar output power ratings.
The Transcription Electronics 211 is divided into three sections: high voltage and bias power supplies, filament supplies, and the audio amplifier section. The coupling capacitors and first stage screen bypass capacitors are Japanese metalized polypropylene variants, as are the primary power supply capacitors visible on the top of the chassis. This is a departure from typical commercially manufactured amplifiers, as most use lower cost electrolytic power supply capacitors. Given that the last capacitor in the power supply before the output transformer handles the signal current in the output stage, it is important to use the highest quality component in this position. These film power supply capacitors also offer a lifetime of over 1 million hours, while the best electrolytic capacitors are a fraction of that. Most of the resistors used in this amplifier are Vishay/Dale. The output transformers and all hookup wire (rated for 1kV) are made in the United States.
Maintenance for the Transcription Electronics 211 is minimal. Expected tube life from the 6EJ7, KT77, and 6CG3 tubes well exceeds 50,000 hours, while 211 tube life is around 45,000-50,000 hours. The 211 amp should be biased at 100mA as indicated on the meters on the front panel, easily adjusted by turning the black knobs on the top of the chassis.
The Transcription Electronics 211 power amplifier sounds musical and open with any high efficiency speaker like Devore Fidelity, AudioNote UK, and Klipsch (ideally with the 4 ohm Transcription transformer), but can also drive any BBC design speaker like Graham Audio and Rogers.
Transcription is very simply converting something from one form to another - the spoken voice actively listened to and typed out - hearing a CD over headphones then writing down the lyrics with pen and paper - or recording a vinyl LP to a reel to reel for broadcast or home enjoyment. Transcription Electronics is a collaboration between Gig Harbor Audio and Paul Birkeland. The goal is the accurate and faithful reproduction of the human voice and music through amplification of analog sources. Our products are the link in the process of transcription and are wonderful amplification for the enjoyment of in-home HiFi. Designed and built in the USA, bulletproof build quality, and constantly evolving products.
-Paul Birkeland & Transcription Electronics / Gig Harbor Audio
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