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Quad II Service


Quad II Service (Quote QIIFS)

Our standard Quad II 130.00 service  includes: 


Fault diagnosis,


Replacement of  cathode bypass and dual can smoothing electrolytic capacitors


 Replacement of signal coupling capacitors with high quality 100n 1000V polypropylene types with copper foil screening. 


Full complement of resistors replaced with High stability, low noise, high tolerance metal film types.


Full performance test and adjustment. Finally after a listening test we carry out a 48 hour soak test followed by a PAT*. We also degrease and clean the case inside and out  to revive the appearance. 

To Service a pair of Quad IIs will cost 240.

NOTE 1: Our standard price does not include replacement of faulty valves or chokes/transformers. We can add valves at cost, and replace faulty transformers and chokes.  The typical costs for new Quad II replacement transformers/chokes fitted inside the original shrouds  are as follows:

Mains transformer: 175.00 extra: Output transformer: 175.00 extra: Smoothing choke 40.00 extra.

NOTE 2: It is highly recommended that you send your Quad 22 and Quad II together so they can be properly electrically tested.  An unmodified Quad II used as a standalone amplifier is potentially lethal without correct earthing. The earthing is normally  completed through the combined Quad 22 mains connector and umbilical cable.  If you want to use your Quad II as a standalone amplifier, please see details of our modification option below.  See further PAT details at the foot of this page.

The images below show a typical standard service for 130.00.



We prefer to use high quality polypropylene coupling capacitors with a copper outer screen to paper in oil types. The copper screen allows a small capacitance to earth to match the original TCC types.*  Well manufactured polypropylene capacitors offer superior leakage resistance and long term reliability than paper in oil types. Audibly and from THD and IM measurements in circuit, the sonic difference between a good quality modern polypropylene capacitor and a paper-in-oil capacitor is quite insignificant. The large HQ polypropylene 1000V types we prefer to use show slightly better THD  and IM distortion levels than paper in oil types but the difference is inaudible (well below the noise floor). We use them because they are electrically superior.

We can fit oil filled types if your prefer at no extra cost but please don't expect a magical difference in sound. A properly serviced Quad II sounds superb whatever type you use!

The replacement of the large grey TCC/Plessey dual 16uF/16uF electrolytic capacitor block, seen on the left in the picture, is often an item of discussion.   Due to the limitations of the GZ32, 5V4,GZ34 rectifier valve, the main smoothing capacitor should not be higher than 16uF for series resistances per anode substantially less than 100 ohms. Which is the case for the Quad II. Any higher value could prematurely destroy the valve. Although 16uF + 16uF seems too low for good smoothing, the clever design, relatively low sensitivity and the large value smoothing choke used for the driver stage HT feed, means there is no need for higher value smoothing.

 The original TCC capacitor block, although it looks quite substantial compared to modern devices, is simply a conventional dual 16uF 450V electrolytic  sealed inside a rectangular box.  As part of our standard  service, we replace the block by a new F&T dual 16uF/16uF 500V cylindrical can electrolytic mounted on a central clip.    Alternatively, to preserve the internal layout, the replacement F&T dual smoothing capacitor can be inserted inside the original TCC case at 15.00 extra per amplifier.  To do this, the old can is carefully unsoldered. The replacement dual capacitor is then sealed inside and wired to the screw terminals. The can is then resealed and re-sprayed.  For the ultimate long life upgrade we can replace the TCC can with two polypropylene 16uF capacitors for 20.00 extra per amplifier.

*This small capacitance prevents the onset of instability manifesting itself as parasitic HF oscillation at the output. This could be why 'component swappers' (not electronic engineers) say they can hear a difference. You can if the amplifier has HF instability!

Modification Options


To add value and enhance the functionality of the Quad II we can fit  a switched and fused IEC mains socket, HQ Gold plated RCA connector and Loudspeaker barrels. We also add an input coupling capacitor. The coupling capacitor modification is  essential if you want to connect your Quad II to a control unit other than the Quad 22. Some preamplifiers/control units have a low impedance DC coupled output and connecting such a unit to an unmodified Quad II will incorrectly bias the first stage. The resultant sound quality is far from satisfactory!

To carry out the modification, the pre/driver tag board is dismantled and moved out of harms way to allow the chassis to be cut and drilled to accept the IEC block and phono connector. The old 4mm sockets are replaced with gold plated loudspeaker barrels.

As there is a mains fuse inside the new IEC block, the old fuse holder and fuse is removed from the rear of the chassis and replaced by a blanking grommet.  This conformal arrangement is much safer.

The mains voltage tap on the rear of the unit is today also regarded as unsafe. As an option,  we can remove it and replace it with a blanking plate. The mains tap is then only adjustable by unscrewing the bottom panel.     

The resulting modification allows the Quad II to be used with virtually any control unit/preamplifier. The convenience of having an RCA input and a mains on-off switch quickly becomes apparent.

The cost of this modification including a full service as above (less valve, transformer and choke replacement) is 180 per amplifier or 340.00 a pair.


If your Quad II chassis needs a face lift we can strip, prime and spray with grey or charcoal, metallic paint. This includes the chassis and transformers, not the bottom plate. The whole unit is dismantled and unwired (gutted) and transformers & choke removed. Add 75.00 per amplifier for this option.


Due to popular request, and to preserve the Quad IIs neat internal layout, the replacement F&T dual smoothing capacitor can be inserted inside the original TCC box case.  To do this, we carefully unsolder the end of the box and wire the FT dual capacitor to the screw terminals. The capacitor is then sealed inside the box and re-sprayed. The original TCC labelling will still be retained. The extra cost for this option is 15.00 per amplifier.



For the ultimate long life, we can replace the box electrolytic smoothing caps with two large 16uF 450/500V polypropylene foil capacitors.

These will offer a superior ESR and lifelong high performance.  They are too big to fit inside the TCC box so they are mounted on a bracket using the four label mounting screws. If you are worried about the internal appearance, the result is very pleasing.

Extra cost for this option is 20.00 extra per amplifier.

More details on above options here

*PAT Portable Appliance Test. A conformal test of the electrical safety of the appliance. This includes insulation test and earth bonding test.A PASS sticker is attached to the underside of the Quad II with the date of the test and the engineers signature. In the event of a fail (very unlikely), the owner will be informed before further work is carried out. 
In the case of unmodified Quad II servicing: the PAT test is performed in conjunction with a correctly wired and serviced Quad 22, or electrical equivalent. The class 1 earth bonding is tested via the Quad 22 mains plug earth pin and the Quad II chassis.   


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Last modified: Monday, 27. April 2015 12:57