Posted on Tue, 13 Jun, 2017
Posted by Bob

Quad Valve amplification formed the foundations of Quad, one of the most historic and legendary Hi-Fi companies.

Formed by Peter Walker way back in the 1930s, Quad forged a legacy of high-performance audio equipment, which still continues to this day. Despite a move to Solid State technology in the late 1960s, the appeal of Quad’s classic Valve equipment has endured.

Today on The Audio Affair Blog, we take a look at the illustrious history of Quad Valve equipment and pay homage to this legendary manufacturer.

Quad – A legend founded upon The Valve

To understand the inherent significance of the Valve in Quad’s history, it’s necessary for us to travel back in time to the 1930s; an era in which the term ‘Hi-Fi’ had not yet been coined, and consumer electronics, very much in its infancy.

The company we know now as Quad was originally founded in 1936 by Peter J. Walker in London, going by the less than memorable S.P. Fidelity Sound Systems. At this period in time, the company’s main output was that of Public Address equipment.

Fairly soon afterwards, In 1936, S.P. Fidelity Sound Systems had its name changed to the Acoustical Manufacturing Co. Ltd, a name which would be rather familiar to many Quad users (more on that shortly).

The Acoustical Manufacturing Co. Ltd only remained in London for another five years, thanks to wartime damage of London. Fleeing the ravaged wartime London, the company moved to Huntingdon in 1941, where the company we now know as ‘Quad’ has stayed ever since.

The move to Hi-Fi – QUAD is born

Post-War saw a boom in demand for equipment we now know as Hi-Fi; a nascent interest in High Fidelity Audio saw companies such as Wharfedale, Tannoy and Leak focus their efforts on producing domestic audio equipment of very high-quality reproduction.

Using the brand name of QUAD (Quality Unit Audio Domestic) – The Acoustical Manufacturing Co. Ltd launched the QA12 integrated valve amplifier. The QA12’s sound quality was notably high compared to units of the period and was subsequently adopted (like may of Quad’s products through the years) by the BBC.

Quad Valve QA12

Very quickly Quad started to make a name for themselves as manufacturers of extremely high-fidelity equipment; it is not unfair to say that the Hi-Fi world we love so much was partly birthed and nurtured by Quad, alongside such luminaries as Wharfedale and Leak.

It was around this time that Quad’s legendary slogan “The closest approach to the original sound” was coined. Peter Walker also went on record as saying the perfect amplifier should be “A piece of wire with gain“. Two phrases which could be used to define Hi-Fi itself.

The Quad II – The Cornerstone of The Quad Valve Legacy

Introduced in 1953 Quad released their Legendary Quad II Monoblock Power Amplifier; a design which unquestionably is one of the true ‘Hi-Fi hall of fame’ greats, and is still revered and coveted today.

One of the prominent designs of the era was DTN Williamson’s amplifier design, a design which influenced many designers, and set new standards with its ‘Ultra Linear’ concept. Peter Walker took elements of Williamson’s designs to create what he called a ‘Super Ultra Linear’ design.

In Walker’s design, local negative feedback from the output transformer was fed to the cathode of the output valves (instead of going to the screen grid). A slight amount of negative feedback is used to reduce distortion, which leads to a uniformly flat frequency response and lower output impedance.

All these design features were incorporated into the new Quad II Power amplifier, which, like the previous QA12 nee Quad I amplifier used the Marconi-Osram KT66 output valve – a signature component in the Quad II Legacy.

Quad II advert Wireless World 1957

Quad Branches out into Hi-Fi Components

The Quad II was to be accompanied by Valve components which were designed to work in conjunction with the Quad II to form a ‘Hi-Fi System’. Introduced at the same time, the QCII Valve pre-amplifier set a pre-amplifier layout which was to endure for decades.

Switching between radio and microphone sources, overall control of volume plus Quad’s now famous filtering and equalisation functions were to become standard features on Quad preamplifiers in years to come.

Period pictures of legendary maverick producer Jo Meek’s studio in London appear to show QCII preamplifiers being used as part of his production tools on such famous records as ‘Telstar’.


Maverick Producer Joe Meek -note use of Quad Preamplifiers

Synonymous with Hi-Fidelity – The Quad II Endured

Quad Valve equipment became almost a byword for Hifidelity sound reproduction. A series of demonstrations, around the world, utilising Wharfedale Loudspeakers and Quad II amplifiers, brought public perception of Hi-Fi. Indeed it’s possible many people’s first experience of Hi-Fi audio, was via Quad II amplifiers.

It’s a testament to the Quad II’s legacy that it continued in production, alongside the new, Solid State 303 amplifier, right up until the 1970s, some two decades after it was first introduced; a remarkable feat for any piece of consumer electronics.

The Quad II story wasn’t over yet, however, and neither was the future for Quad Valve equipment….

The Quad Valve Renaissance and the ‘New’ Quad II

The 1990s saw a resurgence of interest in valve Hi-Fi equipment; many forgotten pieces of Quad Valve equipment were again being dusted off and used and enjoyed. Before too long this led to a renewed appreciation of the Quad II with an associated rise in used values!

Thankfully, since 2005, the Quad II has been available, once again; the Quad II can be purchased as a faithful ‘re-issue’ of the Monoblock original, sold as a stereo pair of Monoblocks.


Quad II Classic Valve Amplifier


The Quad II is available in a number of configurations, some of which are reimagined and tastefully updated to suit the needs of the modern Audiophile.

For the Quad Valve purist, nothing else but the Quad II Classic will do; an authentic reissue of the original Quad II power amplifier, complete with KT66 output valves. The only significant departure being modern input and output connections instead of the original’s ‘Jones Plug’ connector.

If the 15watt output (30 as a stereo pair) of the Quad II Classic isn’t enough, then Quad have updated the design to offer two, KT88 driven, higher powered revisions.

The Quad II-Forty uses a pair of KT88 output valves, along with revisions to the power supply and driver stages, to deliver 40 watts per Monoblock. Likewise, the Quad II-Eighty ups this to 80 watts, with a quartet of KT88s.

Quad Valve Pre and Headphone Amplifiers

For those wishing to add a matching pre-amplifier to the Quad II power amplifiers, Quad offer the QC Twenty Four and QC Twenty Four P pre-amplifiers. Both of which are ‘clean sheet’ hybrid designs.

The QC Twenty Four pre-amplifier range utilises a military grade, ultra duty, ultra long-life 6111 valve. Input switching is carried out via relay switching for minimal signal degradation.

The QC Twenty Four offers two tape loops, four line inputs and an optional MM/MC phono pre-amp. For those purists who listen only to vinyl, the QC Twenty Four P is a stripped-out, minimal circuit version with a single phono input only.


Valves for headphone listening? Why ever not! The Quad PA-One headphone amplifier brings the Quad Valve magic to headphone listening with balanced and unbalanced line inputs, as well as USB and S/PDIF digital inputs.




Quad Valve Integrated Amplifiers

For those seeking the Quad Valve sound but in a more convenient package, Quad offer two, Integrated Valve amplifiers, the Quad II Classic Integrated and the VA One; both offering different design angles.

The Quad II Classic Integrated is essentially a pair of Quad II Classic, power amplifiers, coupled to a newly designed pre-amplifier, all wrapped up in one chassis. 3 line inputs, a selectable MM/MC phono pre-amp and a tape loop, make this a versatile and welcome addition to the Quad II line.


Quad II Classic Integrated

Looking for something more compact, and more affordable? Then the VA One, part of the Quad One range may slate your thirst for the Quad Valve sound in an ultra convenient package.

Integrating a stereo line-input, with modern, digital USB, S/PDIF and Bluetooth aptX connectivity, the VA One is a great way to add some analogue warmth to digital playback sources.



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