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H.H. Scott TYPE 342C FM Receiver
The H.H. Scott 342C Stereomaster was a statement
by Scott about what it could do that other companies couldn't,
namely produce amplifiers that were assemblies of modules, both
integrated circuitry and plug and play boards that permitted
quick substitution in the case of faulty circuits, say the preamplifier,
which might prevent one channel from working on phono, tape
head, or FM.
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Scott introduced the 342C in
1969, shortly after the 341, which had a list price of ten
dollars less the 342C. I don't know how the 341 was discounted,
but from this vantage point, it seems like terribly poor
value, when compared to the Renaissance-like 342C, so profound
are the differences between the two models. |
The 341, a 12 watt quasi-complementary amplifier,
was a step up from the 342B in that it offered a separate balance
control and a defeatable loudness circuit. It is equal to a
260 or a 260B and would be as useful if it had 2000 uf coupling
capacitors instead of the 500 or less. The 341 utilizes the
simplest of all bias and balance circuits, using AC balance
to adjust the circuit. I never touched the settings on this
circuit when I evaluated the 341, not wanting to spoil what
I heard which I liked.
Amplifier Circuits
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The only thing that the 341 shares
with later Scott models is its phono circuit. Built around
an i.c., it is a purely symmetrical complementary circuit.
It amplifies a grotesque little IF driven shockingly bad
multiplex adaptor that is guaranteed to deny you pleasure
when you listen to FM. The indifferent front end supplies
what it should. That same i.c. in the 342C is supplied by
nothing but the best. At 1.9 uv. the 342C meant business.
I own several 342C's and all issues with vintage gear notwithstanding,
the FM tuners are always a pleasure to test. The same can
be said for all of the tuners that use the circuits that
Scott introduced in the 342C and the 312D,
namely the crystal i.f. circuits that are also found in
the 433, the 377, 386, 387, 477, 490, T33S, and the R74S,
etc. |
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Scott used the 25 watt complementary amplifier found
in the 342C in the 499, the 4 channel amplifier built
as a companion to the 433. Several years ago, a Boston
dealer offered the 499 to me. It was the prototype, just
as had been the 433. I got the impression that Scott didn't
build many, and may have sold less...
By utilizing the chassis as a heat sink, a trick first
employed in the 342, Scott avoided the cost and space
required by utilizing a heat sink to keep the output transistors
cool. Some of the early 342C's came with an enclosure
that had no ventilation holes. None were required. The
386, a 1970 model intended to replace the 344 series pushed
the power envelope to 36 watts a side with chassis ventilation
sufficient from the larger cabinet size.
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Other models, such as the 387 saw the use of chassis
mounted heat sinks that were similar to those used on the 260B,
which were of a sufficient size to dissipate its larger wattage
output. Only with the 477 was there a heat sink density that
approached the 344, Scott's first receiver to feature a transformerless
solid state amplifier.
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Between the cool look of the
electrolytic chassis and the rich brown of the plug in phenolic
boards, the 342C has a look that is as futuristic in early
1969 as the 344 was in late 1963. The choice of modules
was an interesting one, for it meant that an entire receiver
could be completely made, save for the boards, which could
be later installed with not much more trouble than installing
a vacuum tube. This is not meant to suggest that the average
hobbyist should tear apart an early Seventies Scott to test
techne skills, for the tone board is a bit trickier than
the rest... |
Power Supply
As can be seen in these images above, the 342C
has two large value electrolytic capacitors, not three such
as is the case in all of its quasi-complementary brethren. In
my review of the Scott
260, I examine the differences between the two topologies
to some length. The 342C, a sterling example of symmetrical
design, uses the two electrolytic cans as voltage reserves for
its working voltages, plus and minus 37 volts D.C., whereas
a 344 supplied a single positive 59 V.D.C. The additional two
electrolytic can capacitors are used in the output circuit as
a coupler that blocks the DC volts from the power supply from
getting into the speakers. Since these capacitors are treated
shabbily by time, it is a must-do to replace them. I suggest
using 2000 uf caps on a quasi-comp replacement, no matter what
you find mounted on the chassis. Symmetrical circuit values
may be increased as well, but you are more likely to find the
installed value to be adequate for its purpose. Never use a
capacitor that has a maximum voltage rating that is insufficient
for the circuit.
Words about the tuner
I have made it clear that Scott's most interesting
tuners came out in the 1970 model year, starting with the 2nd
generation 312D. Minus the classic
front end, and with the stellar 6 filter i.f. instead of the
1.5 uv capable 12 filter i.f. used in the 312D, the 433, R74S,
and other prestige models. But ditto the multiplex adaptor and
the preamplifier, which could also be found hiding in Scott's
economy priced consoles, for that matter.
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The 342C must have put the rest
of the audio market to shame when it came out. I doubt that
the newly released Marantz 17 was any better. So good is
the 342C's tuner that all of the publicity that Scott put
out about it must have been true. It was obviously better
and the superiority was quickly indicated by an indicator
called Perfectune. When perfectly centered on the desired
frequency, the indicator lights, faithfully. On easy to
reach signals, all the better. On troublesome stations,
a reliable indicator of the point of highest return. The
342C uses a computer to sense the point of perfect tuning
and having given the matter serious consideration, I would
use this indicator, when available, above anything else. |
The entire circuit sits on a chip, which is visible
in the photograph below, on the far right.
The 342C offers circuits that were state of the
art in 1969. Largely based on patents that Scott and Von Recklinghausen
developed between 1946 and 1968, the 342C remains the state
of the art, by and large, today. The IF stage in its FM tuner
is so much better than everything else out there that these
receivers and other Scott tuners are valuable tuners that are
more likely to have held alignment because a large factor in
the circuit, the 6 crystal filter, part of IF2 in the diagram
above, won't drift off value. In this alone, an alignment of
the first IF and the 2nd filter/detector will be easy, since
the second IF stage will resonate at 10.7 MHz with a deep suppression
of the heterodyne frequencies that is a subsidiary advantage
associated with the use of tuned crystals. Superior AM rejection
and the inductive power stage coupling first introduced on the
classic IF strip PC131 (312D early version, 348B) give the 342C
the kind of IF stage more typically found in very high quality
communications gear.
Current to the 342C was the 312D, late model,
which used a dual 6 pole version of the 342C IF. With the best
possible front end (3 FET), the 312D
bests the 342C, which uses a single FET and a pair of general
purpose NPNs for the oscillator and the mixer. A Von Recklinghausen
circuit, it is based on cherry picked FETs that were capable
of meeting the requirements that DVR placed on it in the circuit.
His patents on the subject of FET intensification required a
uniform performance standard of a type that we would take for
granted today. The front end in any given 342C was doubtless
one in the 1.9 uv success range on the front end assembly line.
At the bottom end would be the 2.5 uv boxes destined for 341s.
The quality factor here, the FET, is installed on a socket.
This may be useful to those hobbyists out there that want to
get a sense of how far the art of alignment can extend the performance
of the DVR single FET front end. Since it was used in the R74S,
which offers performance in the 1.7 uv range, I can only imagine
that this art can be extended perhaps toward what a late 312D/431
or a 433 reached for, 1.5 uv.
Details
Some of Scott's most ambitious work is found on
the 342C. Certainly none of its contemporaries went to the trouble
of modularity, and Scott may have done so to avail itself of
the parts basket that it had out and about in its instruments
division. Scott was more than a consumer electronics company.
But in some ways, the trouble it took to make it possible for
a service technician in Jamaica to pull a malfunctioning board
and replace it moments later with a freshly serviced one led
to its demise, since it was using expensive technology to permit
the rapid board swaps. For a while, Scott used the quick swap
system on most of its units, including modest changers that
competed head on with low fidelity record consoles that were
made out of plastic and pressboard. In fact, there is a low
wattage clone of the 342C that uses the same parts basket right
down to the power transistor, but supplies a lower voltage swing
to yield 10 watts per side instead of the more robust 25 watts
that the 342C asks of its larger power supply.
In the final days of Scott, that's what it came
down to, and that was the message that was communicated by the
same marketers who had been beaming about Perfectune. The circuit
was still in use, but it was built around 4 discrete transistors
in the last days of Scott. I wonder to what extent the use of
these approaches may have spelt a premature demise for a company
that was competing in an industry that had oriented itself toward
less discriminating, more price conscious types of buyers. Scott
should have stayed carriage, but that's a story for another
day.
The 342C is really a must-have. Its sister, the
382C includes what is the very best AM circuit 'out there.'
With a collection of notch filters that make it possible to
settle in on a frequency on a background of velvet silence,
the tuner offers AM that has better bass than FM and is only
shy a few kilohertz the maximal frequency of FM. The background
of velvet silence works well with the velvet fog of the crooners
that permeate the airwaves.
ed.
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