The German company Thöress Puristic Audio Apparatus has introduced a hybrid mono-end EHT amplifier based on a minimalist topology that combines MOSFET output stages with tube pre-and buffer stages with zero feedback.
At the same time, according to the company’s specialists, Thöress ideology “resolutely ignores the myth that balanced (push-and-pull) technology with XLR connectors and the corresponding cable configuration usually exceeds unbalanced (one-way) circuitry”.
Thöress EHT received an asymmetric triode gain stage on a 6j5gt lamp, supplemented by a buffer stage on a 12HG7 lamp operating in triode mode with a single gain. This is followed by an asymmetric MOSFET stage with a single gain, operating at high idle current (in fact, in class A). This topology was named EHT in Thöress (in German, Eintakt Hybrid Triode — a single-stroke hybrid triode). The scheme is collected using point-to-point wiring.
The amplifier provides an output power of 30, 40 or 50 W at a load (the resistance of the connected column) of 8, 6 or 4 Ohms, respectively. It is possible to adjust the gain (input sensitivity) for this purpose, a 4-position rotary switch is located on the back panel. Thöress reported that with “the same level of sound perfection as in the uncompromising single-lamp ends, the model leaves exotic expensive power lamps out of the game.”
EHT provides flexibility in relation to the load due to its low output resistance and high damping coefficient. The power supply unit of the amplifier has a proprietary ultra-low-noise network transformer. The zone of thermal radiation of lamps was cooled by two coolers placed in the lower wall of the case.
The lamps themselves protrude a little through holes in the upper wall, which serve simultaneously for the exit of heated air. Input switching of the new product is implemented on RCA connectors.The cost of the Thöress EHT amplifier on the European market was 12,950 euro.