EL84's (and the more generic but identical 6BQ5) are classic staples of tube design. They are pentodes intended for audio power amplification and make there home in numerous guitar amp's, mid-60's hi-fi gear and console sets. Any tube guy worth his weight in solder has at least one design using these tubes in his collection!
This design uses 12AX7's on the input side and a pair of EL84's running class AB on the output. A unique design feature allows the amp to be run in either ultra-linear or triode mode at the turn of a switch. The example shown in the picture uses a separate transformer for the high voltage and filaments - since that's what I had on hand. It is totally conventional, stable and easily reproduced. To go with this classic heritage I wrapped the chassis in oak and finished it with several coats of black lacquer. Brushed aluminum knobs complete the look.
The sound is what you'd expect from EL84's in class AB - open, clean and something you can listen to for hours without fatigue. LP's played through this amplifier sound amazing, but thanks to it's 20W output power it does CD's justice as well. Interstingly - like most tube amp's - it makes compressed audio sources (MP3 etc.) very listenable.
Contact me at geoff@bandonelectronics.com if your're interested in this amplifier. This amplifer will be offered as partial or full kit as well.