Restomod Quad II Tube Monoblocks - 15 Glorious Watts of Power!

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Quad II Tube Monoblock Amplifiers - Modernized and Gorgeous - 15W of Glory!

Stereophile calls these amps “a small wonder” and has reviewed them with high marks on many different occasions.

Here's your chance to own a beautiful and tastefully updated classic.

These classic Quad monoblocks are highly sought after and a treat among collectors. They underwent a cosmetic restoration and all connectors were modernized. While I’m a big fan of classic tube design and performance, I have always been put off by the crappy connectors and superfluous outdated features of many classics.

The strange speaker connectors were replaced with super high quality power strips capable of accepting just about any wire in both banana and spade. The typical oxidized and weak RCA connectors were replaced with a very high quality gold-plated type. The two prong power cord was replaced with a safer modern grounded three prong IEC input socket, so you can use any power cord you like. The no-longer-in-use multi-pin connector for powering a proprietary Quad preamp was safely removed.

All of these wiring improvements simplified the internal wiring and improved the overall look of the piece. Custom aluminum plates were manufactured to close up any remaining holes in the chassis.

Both units also received a complete re-spray using a very attractive paint which is period correct in color and texture. The chassis was completely stripped down, sand blasted, and sprayed in a paint booth with multiple coats of primer and finish color.

We also added a power switch (what a novelty :-) ) so you can conveniently power the units on/off without having to physically pull the power cords each time.

Functionally the units were gone through carefully and tested to the full rating for both power and THD and passed with flying colors after some of the filter caps were replaced and upgraded.

Tubes are Sylvania in the input stage and UK made Mullard or equivalent for the KT66. Very desirable!!

From Stereophile:

“Class-A, push-pull Quad II amp used six capacitors, 13 resistors, one choke, two transformers, and five vacuum tubes to convert a line-level monophonic audio signal into 15W of output power, with virtually flat frequency response between 10Hz and 20kHz and no more than 0.1 % of harmonic distortion. The tubes were carefully chosen—a pair of EF86 miniature pentodes for voltage gain and phase splitting (in a single stage), a pair of KT66 "kinkless tetrodes" for output power, and a GZ32 full-wave rectifier—and the output transformer was designed and made with painstaking care.”

Our Testing Process for Amplifiers (Tube) at SkyFi:

We start with a visual inspection of all internal components to make sure there are no signs of stress or aging. Capacitors are checked for telltale sings of bulging or leaking, resistors are checked for signs of overheating or cracking, and tubes are inspected for signs of stress overheating or cracking.

We then power up the unit carefully and run a simple 1k sine wave while monitoring the output on an oscilloscope for signs of distortion or noise. Finally we run the amplifier to its full rated power into the appropriate resistive load provided by our Sencore amplifier tester. If there is an issue, it will usually be noticeable at this point. If it all looks clean we will often test for THD (Total Harmonic Distortion) measured by our Keithley distortion meter, and compare it against the original manufacturers specifications. The amplifier the remains powered on to "burn in" on our test bench for a few hours to make sure there are no heat related issues. If there are balanced inputs available they will also be tested.

We also test all tubes for output gain and leakage on our calibrated B&K 747 tester against the original manufacturers specifications. If needed, the tubes will be replaced from our vast NOS (New Old Stock) vintage or modern inventory.

Final testing involves pushing actual music thorough the amplifier. We've learned over time that some issues are only noticeable to a trained ear while listening to familiar source material. Our test bench has reference vintage Kef speakers that we're very familiar with which quickly reveal any discrepancies. Some amplifiers will then move into our listening room where they are tested with our in-house reference speakers of choice.

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