Pioneer's SX series of
receivers in the 1970's marked the
high watermark of Pioneer's audio
design. They were engineered and
built like tanks and had the looks,
sonics and slam to match. Even if
you're not a fan of Japanese audio
equipment, you've still got to
respect these for the sheer quality
of build they possessed. If ever
audio equipment could be judged to
have been over-engineered, these
were it. And the passage of time has
proven this well.
The SX-450 was the smallest
receiver in the line-up from
1976-78, the SX-1250 being the
flagship at the other end. These
were rated at a very modest 15w/ch
but if you've ever heard one you'll
likely remember that they can punch
far above their weight and still
have enough power to make your
speakers sing with an impressively
tight, dynamic bass and clear highs
without sounding pushed too hard.
If you're looking for a small
vintage amplifier for a second
system, give these some
consideration - of course you lose
some of the features of the higher
end receivers such as the real
wooden trim, and they will run out
of steam relatively early compared
to a large amplifier if you want
high volume levels in a large room.
However, when in good tune and
matched with a good pair of
speakers, these can still make a
very sweet sounding amplifier with
the bonus of a sensitive FM tuner.
As this was the smallest receiver
in the range, it's inherently very
simple. What you might lose in raw
power you do gain from the relative
simplicity of the audio circuitry,
add some good modern audio
components to that mix and you end
up with a very nice sound to sit
down and listen to.
The rebuild
This came to me for a
restoration. It powered up but had
the usual problems with dirty
switches, a sound fault likely
caused by dry solder joints and also
had some minor cosmetic damage with
two of the control knobs being bent.
There was also some minor moisture
damage in places, also the laminate
had started to peel from the side
panels. Most of the display lamps
were blown also. However, with some
care and attention, this can be
returned to as-new condition.
Our SX-450,
photographed in a crowded
workshop today. Not bad for
32 years old, will look much
happier afterwards however..
When I start a rebuild, I always
pull the main electrolytic
capacitors (elcaps are a much kinder
name) and check them for value and
ESR, also pull a selection
throughout the rest of the unit.
Vintage audio equipment, especially
Pioneers, tends to be quite rugged
and even after 30+ years most parts
are still reasonably within spec
and, as I mention elsewhere on this
website, are often able to be left
alone for a while longer. Changing
parts purely on the basis of sound
quality is another matter (as I
mention in the amplifier rebuild
article), but most times things will
still work fairly well if left
alone.
A full re-cap isn't something I
take lightly, on bigger amps and
receivers it very quickly becomes
expensive. Parts individually aren't
terribly expensive but you need to
buy good quality or else there's no
point doing the work in the first
place. Once you start talking about
power supply parts in higher end
vintage powerhouses, the trend is
very quickly bucked, a full set (4)
of high quality replacement power
supply electrolytics for an SX-1250
receiver were over £150 the last
time I checked.
However, this is not a large
receiver and even the largest parts
aren't expensive, as I started
pulling more of them I did find more
which were marginally under value,
part of the reason could be that
whilst these receivers certainly
don't run hot, they tend to get
warmer than the average Pioneer
integrated amplifier from the heat
of the amplifier output and the
tuning scale lamps; not as much
ventilation here, only a row of
vents along the rear of the metal
top cover. Because of the relatively
small cost of replacing every
electrolytic, it was decided to
replace them all.
The power
supply elcaps removed. The
soot mark is from a nearby
power resistor, the heat
from which over the course
of 30 years probably caused
this one to deteriorate
faster than the one next to
it. Only just over 10% down
on value, but enough to make
me think they needed
replacing.
There's around 40 elcaps total in
an SX-450, replacing most of them
isn't a terribly difficult job, just
time consuming; however, there are a
couple strategically placed in the
most difficult places, including one
between the wafers of the input
switch. Changing this one means
removing the switch, and removing
the switch means literally
disassembling the entire front end
of the receiver.
Main selector
switch - this had to be
removed to replace one tiny
capacitor. Still, easier to
clean it this way..
The end panels on these were
laminate, usually it holds up fairly
well but the laminate finish here
was falling off in places as
sometimes happens after 30+ years.
The peeling laminate was stripped,
leaving the plain melamine
underneath. This surface was
scratched with coarse glass paper
and degreased.
The side panels were veneered, basic
tools such as steel rulers, a very
sharp knife and a hot iron are
necessary here. Patience is key here
and if you don't plan ahead you'll
get into a terrible mess.
The veneer I used here was
grained walnut, the same type of
wood finish which Pioneer used on
their higher end receivers. Once you
get into veneering, you have a whole
range of esoteric veneers available
to you, many years ago in a moment
of madness I veneered a PL-550
turntable in Zebrano. However,
grained walnut is relatively
inexpensive and durable and it's
what Pioneer intended to be used on
their audio equipment back in 1976.
Personally, in a purely creative
sense, I like Rosewood - it has a
sublime colour and a very detailed
grain and looks superb when
lacquered and polished and contrasts
well with the aluminium; however,
it's not an original finish and
originality is what we're aiming for
here, deep walnut can look very
good..
Side panel
stripped down to melamine
and scratched to provide
key. Veneer smells very
aromatic when you heat it,
better than any air
freshener..
Usually the edges of a piece are
veneered first, followed by the face
so that no cut edges are visible on
the main face of the piece. On audio
cabinets I tend to do things the
other way because here the edges are
the parts you'll usually see. And
besides, this veneer is quite thin
so once sanded smooth and the edges
mildly chamfered, any cut edges
should hardly be noticeable in any
case.
I want the finish to look rich
and match with other Pioneers so I
usually apply two or three coats of
dye, followed by several coats of
turpentine based wax to seal the
grain, a careful application of wire
wool as needed along the way - the
more time and care you take, the
better the finish. This is a finish
which I usually find blends well
with most other Pioneers, not quite
as gingery coloured as our SX-1250
(inevitably slightly faded after 33
years) but slightly brighter than
the laminate finish on Pioneer
turntables such as the PL-12 which
tends to be too dark for realistic
walnut - a good compromise between
the two. Being a natural finish, it
will also gradually deepen and
become richer over time.
There are a total of 5 lamps in
an SX-450, 3 large lamps for the
tuning dial, and the remaining two
smaller lamps for the 'Power' and
'Stereo' indicators. All but two had
blown - the smaller indicator lamps
are easy enough to find from the
right places but the tuning dial
lamps are wire ended and complete
with rubber holder, not a type
readily available these days. These
are replaced with bayonet cap lamps
of the same power rating, some
ingenuity is needed here to fit the
new lamps/bases into the old rubber
holders.
Dial lamp
assembly. Original rubber
holders are carefully cut
and new lamp holders fitted
into them.
After hours of work, our SX-450
is completed, looks as good as new
and possibly even sounds better than
it did in 1977.
Completed
SX-450. Gold loudspeaker
spike shows subtle sheen on
waxed veneer, you don't want
this stuff to look too
shiny, but it needs to have
a rich finish. The wood
grain will deepen over time,
it contrasts well with the
aluminium too...
...and
another completed SX-450.
This was done quite some
time later, this time I used
different dye and wax
combination and the
resulting veneer is darker,
I do prefer this look.
