9W Triode connection circuit Vacuum Tube Amplifier

At manufacturing this amplifier there was set a task to make easily to the ordinary radioamateur repeated device. Also the purpose was not high power, but high quality of sound in a room of the average size. At designing the mistake when not enough attention addresses on the power supply is frequently done. In fact actually all signal goes not only through the amplifier but also through a power unit. The amplifier and power unit under the current of a signal are connected consistently. Therefore all distortions from a power unit will be in a musical signal too.

Power tube driver is SRPP type, assembled on tube 6N8S (6SN7). This circuit, when operated on the full 340-volt plate supply shown, can drive a single 6P36S (EL500) effectively. Cathode current to 6P36S is Ia=65mA. Grid voltage about -45V. Quality of the capacitor C1 is important. Quite good results with capacitors paper in oil type.

Transformers U type core is made of high-grade electrical sheet steel. The sizes of section are 36x32 mm. Primary winding partitioned in two sections 1-2 and 3-4, every section consists 900 winds of 0.25mm diameter wire. The secondary winding (7-6, 5-8, and 9-10) is wound between sections of the primary winding. Every secondary section consists 120 winds of 0.5mm diameter wire.  Sections of primary winding connected in series, sections of secondary paralelled. One final point of interest with a S.E. transformer is the air gap. This is necessary in order to bring the operating point of the core to the correct region on its B-H curve. Paper spacer 0.2 mm thickness is applied. The transformer is designed on 8 ohm speakers. Power transformers core toroidal type, section 4x4 cm.

So I'll simply say it sounds wonderful, extremely clear and dynamic.

Amplifier circuit
Power supply circuit