One of the longest running British power amplifiers, the Quad II has a legendary reputation and can be considered a definitive and iconic valve design. Launched in 1953, it acquired a matching preamplifier – the QC 22 – in 1959, just after stereo microgroove records arrived. Most of the early Quad II sales were as a mono combination however, only latterly being sold in stereo pairs. It ran up to 1967, when the Acoustical Manufacturing Company replaced it with the solid-state 33/303, a move that was highly controversial at the time and for some remains so even now! It faded away like the British Empire, slowly slipping from prominence and then finally being discontinued in 1970…
Although praised for its classic looks now, the Quad II was actually designed to be mounted inside a cabinet, such as a radiogram, complete with preamp, tuner and turntable on a console. However, it was fully finished and there were no exposed parts; even the underside was covered. The II was designed to work with the QC 22, getting its mains power and signal via umbilical cables coming out of this. The different channels are colour coded (blue for left, yellow for right or mono). Interestingly, the mono option does not sum the stereo inputs, but rather routes the right input through both channels.
Output impedance came factory-set to 15 ohms for the Quad ESL-57 electrostatic loudspeakers it was expected that the amp would be used with, but this can be changed by using a different tap from the output transformer. The amp sports standard 4mm loudspeaker terminals, but the 6-way Jones plug can be inserted upside down and – this causes considerable damage so beware. Indeed, using this little power amplifier with modern preamplifiers isn’t as effortless as many would hope, because there’s no low or high frequency filtering – so equipment with a DC offset or that puts out HF noise may cause grief. The other consideration is the Quad’s low power – 15W won’t pull the skin off a rice pudding, so careful matching to sensitive speakers is essential.
Reliability is a big issue; almost every example will have had some maintenance, and sadly many previous owners like to ‘modify’ them. Passive components like capacitors will have been changed, and the mains transformers may have been replaced – they’re a weak point of the design. KT66 valves are simple to replace and the GZ32s are generally substituted for the easier-to-find GZ34, a Quad-approved mod. Go for originality – untampered with examples are the most prized. Although most Quad IIs were designed for low impedance hi-fi loudspeakers, some were made for 100V line PA operation, meaning the output transformer is unsuitable for hi-fi applications. These normally come with red loudspeaker sockets on both channels (instead of red and black). The degree of originality affects the value of the amplifier – tatty modified examples go for under £500, whereas a pair of mint originals are closer to £2,000.
If this all sounds highly onerous, then one listen to the Quad II will convince you that it’s all worth it. It has a wonderfully plush and romantic sound, with a liquidity that’s truly special. Indeed, there are few valve amplifiers that come close to it in the things that it does well – it makes the best of the rest sound really quite mechanical and uptight. The downside is that there’s little power and so you’ve got to be running really efficient loudspeakers (nothing under 90dB/1w/1m will do) and not be someone with a passion for heavy metal music or electronic dance beats. Best with smooth acoustic jazz, it’s silky and sweet like no other – but don’t expect it to get the party started!