The Bassophon from 1956 is a fully electronic bass accordion for orchestral use. The loudspeaker is integrated in the transport case. The bellows of the bassophone can only be pulled apart at the top. Two strong tension springs cause the bellows to close automatically. Pulling the bellows increases the volume. This is achieved by a pulley which adjusts a potentiometer. On the top of the treble section there are 2 knobs for coarse and fine tuning. With the 3-position slide switch, which is located above the treble keys, the timbre can be influenced. There are no bass keys.
Circuit design in pure tube technology (ECC82, ECH81, EF86, EL84, stabiliser tube 7475, EZ80). The stage with the ECC-82 tube represents an AF tone generator. The pitch is determined by a resistor chain, whereby the resistors are switched to ground by electrical contacts located below the keyboard. The tube 7475 is a stabiliser tube for generating a highly constant supply voltage for the tone generator stage to ensure a high tuning consistency.
The assembly with the tube ECH-81 represents a key stage which is also controlled by electrical contacts located under the keys. It transmits the tone frequency of the generator to the LF amplifier stage with the tube EF-86 without a key click.
The single-ended amplifier stage with the tube EL-84 delivers a maximum output power of 4 watts. A simple tone control (tone colour switch between ECH-81 and EF-80) allows switching from a rather sharp sound (overtone-like) to a more mellow sound (sinusoidal) in three steps. The power supply with two-way rectifier tube EZ-80 provides the anode voltage for this tube unit in a familiar way.
