The K2-W model he acquired enjoyed popularity when it was released as one of the first modular general purpose amplifiers ... In order to power up the op amp and check its functionality, +300V ...

There are plenty of tube amplifiers now being manufactured ... An NE5532 steps in for the op-amp buffer role, making for a very simple circuit. Power comes from a set of four 18650 Lithium ...

or delivered as a two-box pre/power amplifier pairing where the necessary preamp and power amp duties are housed in separate boxes. But the simplest, most convenient and space-efficient option is ...