A simple 300B amplifier. Monoblocks.

My friend, a fan of quality sound, had been using my KT88 amplifier for a long time, but the idea of switching to direct-source triodes had not left him.

In the pantry for a long time lay prepared copper cases, and a certain amount of suitable parts. We decided to use a 300bEH output tube for the project, as it has good power in a single current, the circuitry of the amplifier is simple and has no peculiarities. The bias is automatic. As a basis we took the three-stage (2x 6sn7 - 300b - 5u4) scheme of JElabs, but the tubes were used USSR (2x 6n8sMELZ - 300bEH - 5ts3s). The use of octal tubes in the preamplifier gives the so-called “large-scale” sound. The amplifier is assembled from available components.

The power supply is standard, no special features: 5ts3s kenotron and CLC chain, power transformers are custom made with reduced induction and a decent power reserve, output transformers are Lundhal branded. I try to use vintage carbon resistors where possible, as they sound better. In this case I decided on siemens and BC brands. The output lamp is powered by AC, the background level is minimal and is set with a balancing resistor. After 12 hour warm-up the modes of input tubes were corrected.

The appearance of the amplifier will be finalized by a friend himself under his own design requests, and individual components will be listened to and made changes, he knows how to hold a soldering iron in his hands). The amplifier turned out, as it was intended, with the character of “three hundred”. Detailed “big” sound and soft deep bass, but for my audio requests I decided to use a 2a3 tube, which has a more refined sound than the 300, but about this in another article.