"tony sayer" wrote in message
...
Quad released their famous 303 model way back in 1967 !!

In 1969 it won a Design Council Award.

The 303 delivered 45 watts per channel into 8 ohms loads.

Performance into 4 ohm loads?

It was short circuit safe.

There are no classic SOA or current limiters. How was the output stage
protected?

It used all silicon transistors and exhibited no sign of crossover
distortion.

Par for the course.

The power devices used were rugged planar types, RCA 38494s and 40411s.

40411s were rugged, indeed.

THD measured at the 1 watt level was circa 0.003% and less than 0.03 % at
rated power - ten times less at both levels than Sugden's woeful A21.

OK, that's at 1 KHz. How about 20 KHz?

The 303 used regulated PSU and drove the "difficult" ESL57 with ease.

It ran cool with very low idle current in the output devices.

Compared to the Quad 303, Sugden's A21 was a pile of junk.

The interest in the Sugden amps mystifies me because they seem to be so
backward.


This French page has some good pics of the insides of a Quad 303.

http://cf.geocities.com/quadfranco/a...33/amp303.html

Here is a schematic of the 1970 version.

http://www.geocities.com/quad_esl63/...c/power303.jpg

It looks to me like there is no loop feedback from the output back to
anyplace near the input. Am I missing something?

Yes thats the better one with the diode-less biasing arrangement. We
used to copy that diagram and made no end of them for mates and other
applications

I'm sure PW wouldn't have really minded after all it was spreading the
good word

I re-furbed a pair for my wife's study room a couple of years ago, new
uprated power, output, and PCB caps. New cermet pots, beefed up a bit
of the output wiring and its as good, possibly a bit better, than new
and will last many, many years yet:-)........

The contemporaneous similar US amp might have been the Dyna ST-120 which had
a far more checkered reputation.