A Portable Tube Preamp

In this amazing project by Gregory L. Charvat, two pre-amplifiers are used with a battery powered high voltage supply. The high voltage supply works by creating a square wave with a 555 timer. The square wave is fed into a small audio power op-amp. The output of this op-amp is back-fed into the secondary of an audio output transformer, generating high voltage AC 170V at 40 kHz. This signal is rectified, filtered, and regulated in a conventional sense. The entire system runs on 8 AA batteries and should operate for approximately 4 hours continuously. This article was originally published in audioXpress, March 2010.

The Glass Audio Special edition is a tradition we have retained since the former title was merged with other magazines to become audioXpress. audioXpress still publishes tube-related articles, but we feel this is one of the highlights for our readers and it certainly is among our authors due to the amount of articles we receive — increasingly addressing applications outside of the typical high-end living-room stereos.