The amplifier is built around Mullard’s double tetrode ECC83 tube and beam power 6V6 output tubes.
The adjoining circuit diagram shows a full fledged stereo version of the amplifier, while the following circuit description of a single channel will make the whole concept pretty clear:
The circuit incorporates a resistive input with R1 maintaining a link between the grid of T1 and ground, irrespective of the input conditions, and helping to create a low pass filter configuration in conjunction with ECC83’s internal Miller capacitance. This eliminates the entry of high frequency RF disturbances into the circuit making it as quiet as possible to stray frequencies.
R2 is used to provide the required biasing to ECC83, it's kept in the path of the appropriately calculated load-line voltage of 300 volts.
The amplified signal from the input stage is coupled to the output stage via coupling capacitor C1 and further amplified by the driver stage consisting of the tube 6V6 and the associated components.
To match the driver stage output with the external 8 Ohm speaker, a matching output transformer becomes imperative.
Here, the driver stage impedance of around 5K Ohms needs to be matched with the speakers 8 Ohms. An ordinary 0-6V/230V/500mA transformer will do the job very nicely.
The transformer required to produce the rather unusual voltages for powering the whole unit may be difficult to obtain in the present world.
Therefore, here we wire up two normal transformers to get the desired sets of voltages. The configuration is pretty straightforward and the relevant power outputs become easily obtainable by using two general purpose transformers.
We have purposely employed a separate power supply for the tone control and the LED circuit to avoid messing up the high voltages involved with the tube power supplies.