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Quad 303


Quad 303 Service (Quote Q3O3FS)

Our standard 3O3  110.00 service includes:  fault diagnosis and rectification, replacement of all electrolytic capacitors, out of tolerance components, badly worn sockets, and a 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. Even better, if you have both your 3O3 and 33 serviced at the same time the combined charge is from 220.  On the majority of 33s & 3O3s we receive this is the final cost + return carriage.

NOTE: Our standard price does not include the cost of blown homotaxial output transistors. These are now becoming very scarce.  The cost of these if required will be added at 7.00 per transistor to a maximum of 28.00 extra if both channels are blown. We will inform you if you are unfortunate enough to have faulty output devices. Alternatively we can fit modern 150W epitaxial MJ15003 devices at 4.50 each, extra maximum charge of 18.00. Fitting these can cause HF instability so we may have to add compensation caps. 

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The images below show a typical full service for 124 inc. two homotaxial power transistors.

Before fault rectification and refurbishment: right channel defunct, crackling on left channel, two main smoothing capacitors leaking and there are several faulty & out of tolerance components.

New smoothing and output capacitors are fitted in place of the old style bracket mounting types.

In the featured repair; two new driver and two output transistors were replaced during the fault rectification process. In addition, five noisy preset resistors and a complete set of electrolytic capacitors were fitted as standard.

On older 303s we fit a tiny BIAS modification board in place of the crude  diode bias arrangement. This allows more precise adjustment of the output transistor bias. The original 0.68-1uF electrolytic or tantalum coupling capacitors,  are replaced with polypropylene/polyester foil types.

Some 3O3s we receive for service are in a very poor state. e.g., rusty case, bottom plate and front panel. We can restore the overall look by stripping and re-spraying these parts with primer and top coat. The re-sprayed sections (cover and bottom panel) will be in two tone metallic colours but will not be perfectly colour matched. The cost for stripping the old paint, priming and re-spraying the cover, bottom and front moulding, if applicable, is 70.00 extra.


Modification Options


To add value and enhance the functionality of the 3O3 we can fit a professional steel powder coated front panel with gold plated, phono inputs, conformal loudspeaker terminal posts and a switched and fused IEC mains socket. Instead of the old flickering mains neon we fit an led to monitor the  HT rail voltage. When the power is turned off the led slowly dims indicating when the internal capacitors are fully discharged.  This is useful when you want to move the unit or disconnect / connect loudspeakers.  DETAILS


If you want the ultimate (still a Quad 3O3) modification we also offer a complete full component replacement option. We fit a new front panel as above and  strip the L & R signal and PSU boards and fit new components throughout. No old electronic PCB components are used apart from the bare boards if they are good, and the internal heat sinks. If the boards are poor, we can replace these too for an additional 20.00.  The circuit is still Quad's original but with new components. The net result is a more robust 3O3 with improved response, lower noise floor and distortion and improved power handling capability. The well loved slightly warm 'valve like' sound remains. 

Alternatively our completely new circuit upgrade option is available.



*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 303 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.


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