Quad 33/303 Amplifier
These amplifiers were made from 1967 and had a production run of about 15 years. They were one of the best amplifiers around at that time for both design and technical performance. Both the 33 pre-amplifier and 303 power amplifier are readily available on e-bay which reflects their good servicability. Even if they go wrong (which is rare) they can easily be serviced by Quad or indeed anyone else for that matter. Because the design is relatively simple plus a well thought out modular design (individual circuit boards are removable) then repair is much easier than say the average Japanese amplifier and accounts for why there are so many Quads still running. Personally I think that these are fantastic things to own - I have had serveral sets all of which worked well but I decided only to keep one 33 and one 303 that are in pristine condition. There is loads of information on these amps on the internet and lots of people offering upgrades so if you purchase one of these amps it can be maintained in servicable condition for a very long time - maybe several more decades!
Quad 33 Pre-Amplifier
These require some thought before use - not least because the use DIN rather than phono connections. Best to see if you can get the required leads (including the special Bulgin mains connectors) from the seller. Otherwise you will have to buy them separately - I recommend flashbacksales who do really good quality leads for the Quad. Problems to look out for on the 33 are incorrect operation of the on/off which is part of the volume control and intermittent noises. The later can be fixed by removing the circuit boards cleaning the contacts and replacing. Use of proper switch cleaner is recommended for the switch assembly and volume/tone control potentiometers. Sensitivity is quite high on the Quad inputs at around 100mV so use of a CD player etc required either a modification to the Disc board or (more preferable) an attenuating lead to play back through the Radio 2 input. If your fussy I recommend looking at the circuit (diagrams readily available on the net) and changing the disc input to 47K as against the standard design which is 68K which gives a smoother sound with most MM cartridges. Also for each board you can carefully replace each of the electrolytics with equivalent new ones of the correct voltage and capacitance. Its a fairly long painstaking job but does return the sound to its original standard Check when buying that the bacl panel is not damages - the flaps which access the removable tape and disc input boards ofter break. The case can suffer paint loss around the volume control and the metal enclosure is often scratched and can even rust!
Quad 303 Power Amplifier
These really are the most robust part of the amplifier package - its almost impossible to damage them through abuse. The build quality is really to industrial instrument standards. Externally look out for scratched paint and bend heatsink fins - I would prefer a cosmetically perfect example even if some internal repair work is required but it doesnt matter really. Also I prefer not to see the amplifier modified with phono sockets but again thats just a matter of choice. Internally the four large electrolytic capacitors should be replaced as a matter of routine to prolong the life of the amplifier. Also just like the 33 the smaller electrolytics on the circuit boards can be replaced to improve sound.
I find the sound of this combination very detailed with good punchy bass. I would say its sound quality is different from modern amps possibly due to use of a large number electrolytic capacitors in the signal path. I suspect that the 33 has more of an influence over the sound than the 303 but I have not checked this. I have done a frequency response check on my own set through the Radio input on the 33 and it is incredibly flat from about 30 Hz to 20KHz. I think that the Quad 33/303 coupled with a CD player (suitably attenuated) and a pair of compact speakers makes a really neat second Hi-Fi for an office or bedroom.