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This page presents the "MUSICIAN'S AMPLIFIER and its later version - the "MAESTRO" AMPLIFIER.

Both of these amplifiers are modified and improved versions of the original Williamson Amplifier.


Details of the Musician's Amplifier were published in the November 1949 issue of US magazine "Audio Engineering", in a paper authored by David Sarser and Melvin Sprinkle.

The Musicians Amplifier - (original November 1949 paper)

Grateful thanks to Ian D. Baren, a personal friend of David Sarser, for providing this document. (Contact at  www.katonahhardware.com)

David Sarser was a violinist with Toscanini's famous NBC Symphony Orchestra, so was able to offer a "musician's" ear and sensitivity to the team.

Melvin Sprinkle was an experienced electronics engineer and contributed the evaluation and tweaking of the Williamson design.

Sprinkle's electronic expertise coupled with Sarser's musical sensitivities were essential to improving the science of Williamson's design into musical art. His engineering stature was to be recognised by his becoming a Chartered Member of the Audio Engineering Society of the USA.

It is clear from the text and circuit design that this amplifier is an improved variant of the by then well accepted April/May 1947 and August 1949 "improved" Williamson design - adapted to use US made 807 tubes instead of the original British KT66.

They also considered the results of intermodulation distortion analysis of the Williamson, published in the September 1948 issue of "Audio Enginnering".

They would most likely have also seen the Australian AWV Radiotron A515 design, published in the Nov/Dec 1947 issue of Radiotronics magazine, as well as other commercial variants.

The Musician's Amplifier is shown below: (Open in new window for full size graphic)

Note the reconfiguration of the B+ decoupling system, including elimination of the filter choke between output tubes and driver tubes.

The Power Supply for this amplifier is shown below:

Note the capacitor input to filter rectifier system. This allows a lower voltage transformer secondary and therefore a smaller, cheaper transformer. Switch-on surge voltage is less so the electrolytic caps can be of lower voltage rating. The original Williamson power supply used oil-filled paper caps that deliver better sound quality than electrolytics.

Importantly the B+ voltage has been reduced from 450 VDC to 400 VDC. This would reduce power output.

Power output is likely to be around 10W rms.


Some reports suggest the Musician's Amplifier was produced commercially in the USA as the Heath WA-1.


Details of the Maestro Amplifier were published in the November 1952 issue of US magazine "Audio Engineering", in a paper authored by David Sarser and Melvin Sprinkle.

The purpose of this amplifier is to increase the available power from about 15 watts to around 90 watts rms.

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Maestro Amplifier Schematic

Maestro Power Supply Schematic

This amplifier is not triode connected as is the case with the conventional Williamson variants, but is included here for historical reference because it uses the same front-end circuitry as the Williamson.

The article commentary explains the purpose and justification of this design.

The Maestro Amplifier is one the few commercial amplifiers that captures the audio application capabilities of the truly outstanding 6146 Beam Power Tube.

Note that the GEC, Heathkit and Dynaco variants of the Williamson offer ultra-linear output stages, which most people would find superior sounding than the Maestro.

However due to the limitation of screen-grid voltage with the 6146 tube the Acrosound 100 watt ultra-linear amplifier design with tertiary winding for the screen-grids is the safe way to go.

6146 tubes will not tolerate high screen-grid voltages - i.e. greater than 250 VDC - which eliminates the option of using them in a conventional triode connected Williamson or in a conventional ultra-linear configuration.

However in my humble opinion there are few vacuum tubes that will deliver a superior performance in audio applications.

So if your taste includes pentode connected output tubes then the Maestro is for you.

Improvements available to the Maestro Amplifier include a solid state FWB rectifier, large filter capacitors, filter choke to driver stages.

Note the 6146 tube is available in a 12 volt heater version as the 6883B - usually somewhat cheaper to acquire than the 6146.

There are also other variants of this very reliable tube.

Note also that short plate leads are desirable to minimise self/parasitic oscillations.

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This page last modified 10 November 2010