Monday, May 3, 2010
KT88 Bread Board amp with no driver stage.
This is the first bread board amp (said Be Bamp) under the retro-thermionic brand so it had to be a different to other BB amps and stand out. Also it was designed to be used with a high gain preamp because, in this model, there is no driver stage. It has been tested with the retro-thermionic Tea Box two stage valve preamplifier. Also all wiring is hidden under the board to give a clean neat look. To further enhance the look the two open OPTs are housed in a metal enclosure. The enclosure doubles as a mounting point for speaker and input terminals, all gold of course.
The driver stage has been removed to reduce the number of stages the music has to travel though before appearing at the speakers. This has resulted in an increase in transparency and detail. In future releases of the Be Bamp a version with the driver stage will be produced.
Though the wiring is hidden there is plenty of components above board. Also the high voltage (400V) rectifier is exposed so electrocution is possible both here and from other components. For a twist the HT standby switch, which must not by operated under one minute of warm-up time, is covered with a red rocket launcher cover. The board is Australian Pine and has been treated with Australian beeswax.
Main components are Hammond (over specified) power transformer and 10H Hammond, high current, choke. Edcor open OPTs are used. The Be Bamp will work with a number of different valves; 6V6GT, and EL34s being just two. A matched pair of JJ Blue Glass KT88s are shown in the image. The amp will produce about 5W if driven fully.
The retro-thermionic Fostex Back Loaded horns were used to evaluate the Be Bamp. Voice and all acoustic instruments display a very dimensional sound with voice sounding crisp and earthy with very controlled sibilance. The amp is absolutely hum, buzz and hiss free and is the quietest amp I have ever built. With a result of the deepest black back ground well know tracks sound new again and display extended fine grain detail.
On request retro-thermionic will provide this amp as a kit with rectifier module and power valve module assembled and tested. Ever part will be provided for the DIYer to assemble.