Tuesday, July 20, 2010

6AS7 SET amplifier

This very special, one of a kind, SET is based on the 6AS7 twin power triode. A two stage amplifier with a 12AX7 driver. Only two valves in the audio circuit and valve rectification. The rectifier valve is a rare JAN CBXL-5R4GY (brown base). The power valve is an English United Electric and driver valve, 12AX7 Australian made AWA.

Valve rectification and a reactor filtered power supply ensure true musicality. Combine this with an internal power filer, vibration isolated power tranni and OPTs. This makes a very quiet and dynamic amplifier.

There is no input capacitor. The critical inter-stage capacitor, joining the driver stage and power stage, is a large and expensive Jensen, pure copper, paper and oil type. Silver wire is use to bring the audio to the driver stage and component-2-component wiring is used throughout. No PCBs exist in this amp!

After much listening I am convinced this is the best amp I have ever built. Not only based on its detailed mid-range and extended highs but its deep and weighty bass. The volume of bass I was not expecting. The sound stage is deep and wide both behind and in front of the speakers. Sibilance is natural and sustain and reverb. extremely well rendered.

A lovely Mirbeu timber base (custom built especially for this amplifier) holds something very different. A blue top plate carries exquisite but bulky componentry. Though only a few watts, with the right speakers this simple amp will delight and surprise you. With a frequency range from 12hZ to 50,000hZ it is easy to understand why this amp sounds so good. And why the bass feels extended and full. I true audiophile SET amp.


Anonymous said...

Hi !
this is an outstanding job !
You didn't say a word about your output trafos
What about their caractéristiques

retro-thermionic said...

Fred: The OPTs are Edcors and are tiny because the 6AS7 has a very low plate impedance. The sound characteristics are good extended bass, absolutely breath taking mids and smooth highs. Drives most reasonably efficient speakers well but doesn't like capacitive loads.

Anonymous said...

Hi - well done! Like your execution of this amp. Interested to see the schematic and operating conditions of the 6AS7?? Cheers, Grant

retro-thermionic said...

Take a look here: http://www.diyaudioprojects.com/Forum/viewtopic.php?f=9&t=2243&hilit=+6AS7

Anonymous said...

Hi, Great job on the amp. I've seen the tread over at diyaudioprojects and I am interested in building this amp. But I would like to parallel the grids, plates, and cathodes on the 6as7 for more power output. What would I need to change to accomplish this and would it be worth while to do so?


retro-thermionic said...

I'm not sure you would get much more power from the amp with parallel plates and I don't know what you would change if you did. Sorry.