TUBE-TECH HLT 2A is a stereo unit, featuring low and high cut filters, low and high shelving filters and a T-filter. The shelving filters are designed around a high gain tube amplifier. The T-filter is a passive filter placed between the shelving filters and the output amplifier. All three sections are supplied with a in/out switch. The low and high cut filters are also passive with a slope of 6dB/octave.

A bypass switches the whole filter section out of the amplifier circuit, keeping the output stage in the circuit. The T-filter is like a seesaw. When the low end goes up, the high end goes down and visa versa. When the potentiometer is turned clockwise, the high frequencies are boosted and the low frequencies are attenuated. When the potentiometer is turned counter clockwise, the low frequencies are boosted and the high frequencies are attenuated.

The unit is all tube based except for the power supply. Input and output have fully floating transformers. All DC voltages are stabilized, except the anode voltage for the output stage.