Decades of Musings on HiFi

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Article

This Is How to Turn an Edison 60 Kit into a 300B Amplifier

Converting the Edison 60 amplifier to 300B output valves, by Thorsten Loesch.

Original title: The Edison 60 Kit Amplifier with 300B's

Published here · Original date: not recorded

Edison 60 - 300B300BEdison 60 Kit

This 300B Parallel Single Ended (PSE) amplifier is based upon the Edison 60 amplifier kit, which is made in the UK. This modified version uses the PCBs from the Edison kit with only minor changes. The biggest changes are in the PSU.

Photograph: the finished amplifier, a polished steel and black chassis with wooden side cheeks, two 300B valves and two small driver valves per side
The converted Edison 60 with four 300B output valves.

The driver stage is similar to that of the Audio-Note P4. The input valves found to sound best were old production Tesla E88CC (goldpin) and General Electric 6CG7 (think of it as a 6SN7 in a 9-pin bottle). In general there is nothing unusual about this circuit.

Schematic: 300B PSE amplifier, one channel, a 6CG7 input stage, an E182CC cathode-coupled driver and two parallel 300B output valves with a 2.4k output transformer; specifications listed beside the output stage
The amplifier circuit, one channel. Parts notes and specifications are on the drawing.

The rectification is solid-state with extensive filtering, as described by John “Buddah” Camille.

Schematic: power supply with a bridge of eight MUR480 diodes, a multi-stage filter with chokes and filter capacitors, and separate 6.3 V heater windings
The power supply and heater arrangement. Notes on capacitor types and on using the Edison 60 mains transformer are on the drawing.

A pair of Svetlana SV300B valves per channel produce about 18 watts per channel. Heaters are all AC, the noise on the output is around 2 mV. The sound of the Edison amplifier with 300B output valves in PSE zero feedback operation is more alive, more vibrant and dynamic than when using the EL34. The high range is sweeter and all in the amplifier is considerably improved. Highly recommended.

Photograph: rear view of the amplifier
Rear view of the amplifier.

My review of the original, EL34-based Edison 60 kit, written for TNT-Audio, is here: Building and listening to the Edison 60 Amplifier Kit.

Note on this page. The text is from the original page on my Thunderstone Audio site; I corrected one spelling mistake and left out the address of a UK supplier from the early 2000s, which is long out of date. A later republication of the page on the kit supplier’s own site carried added passages about parts supply that were not mine. They are not reproduced here.

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