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OPTIMISED ELECTRON STREAM © TECHNOLOGY

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AUDIO and RF MODULATOR

TETRODE, PENTODE AND BEAM POWER TUBES

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ACROSOUND
"WILLIAMSON"
AMPLIFIERS

This page presents details of triode
connected and ultra-linear "Williamson" amplifiers produced by the Acro
Products Inc USA

Acrosound Williamson Amplifiers.

In 1936, Alan Blumlein was granted UK Patent
496883 covering a design concept describing a particular form of loading
configuration for power tetrodes, pentodes and beam power tubes in electron
tube amplifiers whereby the Screen Grids (Grid 2) are fed from a tapping in the
primary Plate winding, or from a separate discrete Screen-Grid winding, of the
output transformer.

Later, writing in the November 1951 edition of
the US "Audio Engineering" magazine, David Hafler and Herbert Keroes of the Acro
Products Company, USA, used the term "ULTRA-LINEAR" to describe a specific form
of this mode of operation.

It could also be reasonably said that the
1950/1951 Hafler and Keroes of the USA upgrading of valve hi-fi amplification
to their ultra-linear output stage configuration was yet another stage in the
evolution of the remarkable Williamson Amplifier project.

US Patent 2680218, granted 1 June 1954, covered
their ultra-linear transformer design. Then on 7 June 1955 they were granted US
Patent 2710312, covering the 43% turns ration for optimum U/L
performance.

Then on 7 May 1957, Acrosound was granted US
Patent 2791646 covering an improved ultra-linear confiuration whereby the screen
grid windings were separate to the plate windings, thereby enabling the
application of different plate and screen DC voltages - a useful feature for
high power applications.

Acrosound said: "The Ultra-Linear Williamson
arrangement with the Acrosound TO-300 transformer doubles the power of the
triode version for a given distortion and also provides better transient
response as evaluated by square waves. This circuit has been described in Audio
Engineering, June 1952 and Radio and Television News, February 1953."

An even higher powered design using US made 6550
valves instead of the British KT66 was published in the November 1955 edition of
Radio and Television News. (Copy below).  Note the KT88 valve was yet to
come.

The 1955 Acrosound USA Transformer Catalogue
offered no less than three variants of the original Williamson - 12 watt triode
or 25 watt ultra-linear with (interchangeable) KT66 or 807 valves, and a 50 watt
ultra-linear version with 6550 valves delivering 50 watts output. It also
offered a 100 watt
ultra-linear amplifier (not Williamson based) having the latest transformer
design using 6146 valves with separate plate and screen supplies - one serious
piece of valve audio amplifier !!

For full sized images open in new window.

Acro Triode or Ultra-linear connected
Williamson with KT66 or 807 Valves:

Acro Ultra-linear connected Williamson with
KT66 or 807 Valves:

Acro Triode or Ultra-linear connected
Williamson with 6550 Valves

Performance of the above 6550 version of the
Williamson amplifier is stated by Acrosound as:

Acro Ultra-linear connected Williamson with
KT88 or 6CA7/EL34 Valves

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http://www.oestex.com/tubes/acro.html

This page last modified 06 July 2010