This tiny preamp really adds warmth and richness to the sound. The build quality is good. Inside you can see a neat circuit board. A 555 timer chip and several rectifier diodes are used to convert the 6V input voltage to high voltage (using the multimeter test as 105V) to light the lamps. The input and output coupling capacitors are Rifa 426, which are considered Hi-Fi. The bass and treble control is a simple classic passive Baxandall tone control. This is a single stage tube preamp, no other stage uses op amp ICs. So I think it's a pure tube preamp. Rebuilt with GE bulbs, works like a charm.
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