Re: Audio Anateur Magazine Back Issues

Ted Rook

Those with an interest in the gruesome details of tube amplifier design may enjoy this article
published by Williamson in Wireless World in 1952 following some exchange of opinions
between UK and US hifi amplifier makers

My first hifi amplifier was a Quad tube set. It is long gone.


On 29 May 2018 at 16:52, Richard Knoppow wrote:

Williamson was famous for his driver circuit. His original
amplifier used triodes or triode connected pentodes. The circuit
was modified a few years later to improve its stability and get
rid of some spurious oscillations. When the Ultra-Linear output
circuit came out the amp was again modified to take advantage of
it and I think this is what you are thinking of. Dyna published
an article by David Haffler on how to make the conversion and
Dyna or maybe it was Acrosound, made a suitable transformer.
Look through the material on and also
magazines on American Radio History.
Sometime around the mid 1950s the increased dynamic range of
recordings made increased power advantageous. The low efficiency
speakers that began to come out after stereo was introduced made
further power increase desirable. Charts from the 1940s for
motion picture theater sound show that power on the order of 10
to 20 watts was considered sufficient for theaters of 500 to 1000
seats! Efficient speakers and limited dynamic range was the
reason along with the high cost of amplifier power. By the mid
1960s 10 watts was considered a toy and home amplifiers of 50
watts were commmon. It does make a difference if the amps are of
good quality.
The conversion of an early Williamson amp to an Ultra-Linear
output just about doubled its output power.

On 5/29/2018 1:24 PM, r221b@... wrote:
If I recall correctly, the old HH Scott LK-72 amplifier was 40 watts (per channel) and used the Williamson output circuit. Maybe that can help you? Don't have the AA magazines though. Rich
Richard Knoppow

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