I have a quad 303S. All capacitors are replaced with new ones, and some resistors will be replaced with new ones. The amp is in mint condition. I have searched the internet to find some information about the 303S, but I can`t find anything about the "S" model. The production number is around 22000.
The curcuit diagram I found on the internet is different is not the right one....
Anybody who knows anything about the "S" model?....
The curcuit diagram I found on the internet is different is not the right one....
Anybody who knows anything about the "S" model?....
Are there physical differences in the 303S that lead you to believe they are a different circuit?
It appears to be in the standard serial number series so any differences should not be great.
Some pics for interest:QUAD 303 Amplifier modification to general purpose Lab amp from 303 A2
It appears to be in the standard serial number series so any differences should not be great.
Some pics for interest:QUAD 303 Amplifier modification to general purpose Lab amp from 303 A2
I can only find two transistor om the powersupply curcuitboard, one small and one bigger, but on the scheme I found on the the internett, there are two. Some of the capaciotors are also different, compared to the one found on the net.
The PSU board on my 303S has only two!
One small round transistor, and one with a heatsink.....There is not a third one!!! Perhaps my 303S is something special?
Are there any Quad specialists out there? ............
If you look at the schematic(s), the dashed line indicates which components are mounted on the circuit boards. You'll see that the third transistor (tr3, part #40411 which is in a large TO-3 case) for the power supply is outside of the dashed lines, and is, therefore, not mounted on the circuit board, but rather on the heat sink. (I just went and checked my 303, which is a serial number in the 60 thousands, and it only has 2 transistors on the PS board) Beyond that I can't tell you what the 'S' means, but since the amp was made from 1967 to 1985, in a quantity of 94,000 units, there were changes to AC input, DIN versus RCA, and speaker outputs so I guess your 'S' is one of those.
Try e-mailling Quad.
S in the UK usually means Special. It's possible it's had a few tweaks but I woulndn't expect it to deviate too far from the original.
S in the UK usually means Special. It's possible it's had a few tweaks but I woulndn't expect it to deviate too far from the original.
I will take some pictures this weekend. The guy who gave me the Quad set bought it in the late sixties. He also bought a Thorens 124 II. The Thorens did not work, because the motor was defect. A SME3012 arm was mounted, and I sold the Thorens and arm, to a collector who had six others 124, for about 10000 Nkr, about 1100 British Pounds.
Pic 1 shows the bottom of the main heatsink and leads to the lower power transistors. There is a cover running up the centre of the heatsink on the outside. Under that will be 5 TO3 power transistors; 2 each for the power amplifiers and the last, TR3, is the main regulator for the PSU. That is the third transistor you suspect is missing. The regulator could not supply enough current without it.
From the little I can see in the pics, this is likely a standard 303 with all different connectors as prairieboy suggests. This may have been necessary to suit European standards at the time - compare Keith Snook's pics, linked in post #2. It is quite likely that capacitors have been replaced in amplifiers seen on the web, either because they had deteriorated or the owner wanted to upgrade. In any case, over 18 years production, I would very much doubt that all components remained available or even looked the same. e.g. it would be necessary to always fit fresh stock electrolytics.
If you want confirmation, it would be best to contact Quad directly and they can check from their archives, as they probably have retained sufficient details.
From the little I can see in the pics, this is likely a standard 303 with all different connectors as prairieboy suggests. This may have been necessary to suit European standards at the time - compare Keith Snook's pics, linked in post #2. It is quite likely that capacitors have been replaced in amplifiers seen on the web, either because they had deteriorated or the owner wanted to upgrade. In any case, over 18 years production, I would very much doubt that all components remained available or even looked the same. e.g. it would be necessary to always fit fresh stock electrolytics.
If you want confirmation, it would be best to contact Quad directly and they can check from their archives, as they probably have retained sufficient details.
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Big film cap on the PSU board looks like it wasn't installed by Quad. Other than that, the PSU board looks typical. The 'face plate' is different in not having the typical voltage changing plug in the upper right hand corner. Also doesn't seem to have the 'standard' pair of banana plugs. Caps with the connections mounted 'down' was used earlier in the production runs, later changed to being on top. My unit has a bridge rectifier, this one shows four individual diodes, but I can't comment what was used over the life of the 303.
I;m digging out pictures of the guts of one of mine... TLS.org | Quad 303 monobloks
Of the top the difference is the DIN speaker connectors instead of 4mm for banana plugs. It also has a captive AC cable.
Officially imported (into Canada) 303s did not have a voltage change switch.
dave
Of the top the difference is the DIN speaker connectors instead of 4mm for banana plugs. It also has a captive AC cable.
Officially imported (into Canada) 303s did not have a voltage change switch.
dave
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Mine was bought in Oslo in 67-68. Is it possible that Quad was selling the "S" model in Norway as well?
I'm intrigued as to why you want to restore a Quad 303. The circuitry in them is so dated and the sound is really quite dead, dull and boring.
For the same reason a person would restore any older amp, tube amp, vintage speakers, old car, tractor. In that same vein, why even bother with DIY?
It's odd that Quad used to say something like "Perfect is only good enough", Sadly their products don't match their promise.
I have removed the old open-type pot.meters, and I wonder.....When I are adjusting the pot.meters on ps-board and amplifier-boards, do I have to do anything, like short-curcuiting the input, and do I have to connect loudspeakers to the amplifier, when adjusting the pot.meters?
I will use the instructions I found on NET Audio
I will use the instructions I found on NET Audio
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