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H.H. Scott TYPE 312 FM Tuner
| The H.H. Scott 312 Stereomaster
was intended as the successor to the 310E
and was designed to suit a significant niche that Scott
occupied, that of supplying the FM broadcast industry. That
industry used Scott 310's of
one sort or another. FM networks used them to receive a
distant signal that in turn would be rebroadcast at a different
frequency. Line of sight results made possible by high mountains
could render a clear signal from a transmitter up to one
hundred miles away. |
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| The 312 is a slimmed-down version
of the 4312. Although the IF circuits differ, the tuners
share a nuvistor front end that makes them different beasts
from any tube or solid state that Scott made before or after
the 312. If there were one way to improve the 4310
it would be by the use of a nuvistor front end. I suggest
that it would be an interesting modification. A compact
tube that compared in size to a transistor, the nuvistor
saw use in a variety of industrial circuits where its compact
size, ruggedness and low threshold noise made it a preferred
choice in demanding applications. |
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The nuvistor saw little use in audio applications.
McIntosh used a pair in the front end of its MX series of tuners,
and Scott used the tube for two years (1963-65) in its premier
line of tuners, including the 4312, 312, 344, and the 348.
Low cross modulation in excess of -65db yielded front end performance
that tuners equipped with a 6BS8-6U8 front end could not match.
The tube equivalent to the 4312, the 4310
has a maximum sensitivity of 1.9uv and a maximum channel separation
of 30db.
The 4312 series of tuners match the 4310's
sensitivity but add an extra 5db to the attainable channel separation.
The 4312 series upped the detector bandwidth from 2 MHz to 3
MHz, this attributed to the use of transistors.
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The 312 is the penultimate hard wired Scott. Even its
sibling, the 344 had printed circuit boards in its phono
stage.
The first generation 312 shown here retains the tuner
geometry of the tube era. The next, the 312A positioned
the IF strip alongside the multiplex adaptor, extending
it away from the front end that it straddled alongside
in the tube tuners.
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Back in the days of FM networks, it was common for a
broadcaster to have a stack of tuners set up to feed a
transmitter. These tuners might carry signals from different
members of the network at different times and a technician
or a timer might switch between the tuners according to
a schedule, or the tuners might all be employed to receive
the same frequency with antennas with different orientations.
These tuners all fed a diversity system that would select
the best signal from the bunch. Scott's 4310
had a diversity computer built into it. One was needed
to control the selection of the strongest signal from
the group of tuners.
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It's interesting to think about H.H. Scott as a maker
of industrial art, or audio sculpture. The whole styling
aspect of the middle period of Scott tuners (from 310B
to 310E) was oriented by the
use of the vernier as a tuning dial. Scott was alone in
doing so, and the impression that one got from looking
at a 330 or a 331 was of a mid '20's Browning Drake TRF
set.
But style as an object is always part of a finished object,
for obvious reasons. We tend to find the best examples
of industrial design in devices that are intended to be
used for non-casual purposes. It may be slavishness to
the object of good design that saw Scott place the IF
strip in the same orientation that it has in its tube
predecessors. The next iteration saw the IF strip oriented
in a manner more consistent with the actual layout of
a chassis instead of one consistent with the front end.
I suppose it didn't matter.
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The Scott 312 was intended to replace the 310E.
Both tuners were up for sale in 1964. Both have the front
panel style that was current from 1963 into 1967. There
was a significant price difference between the tuners,
but this is not apparent in performance, where the only
tuner that outclasses it is the 310E. I imagine that the
312 front end in the 310E would further distance the two.
I imagine that when they were new, the phenolic based,
later issue 312s sounded as nice as the hardwired 312
does. But with the passage of time, phenolic boards warp
out of shape and begin to rot. Since almost all of Scott's
solid state circuits were assembled on PC boards that
were made out of phenolic, many of its solid state tuners
are affected by a rotting that can change the value of
electrical circuits. This problem varies from location
to location, so Scott receivers from Arizona may fare
better than those that were listened to in Florida.
1964's 344A receiver was the last hurrah for hard wiring.
It used phenolic in the phono section and in the amp driver
stage, visibly attached to the oversized heat sinks. It
shared the IF and multiplex adaptor stages that were used
in the 312 and featured a front end that when implemented
in the 344B with FETs instead of nuvistors, would serve
as the basis for all Scott tuners post 312D.
The shared parts basket made it possible, of course, to
tweak the IF and obtain the same performance as one could
expect from a 312 that would have been aligned more closely
by the factory.
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Much of the time that I spend listening to FM is dedicated
to CBC Radio 1 and 2, but I also like to tune in the weaker
stations, like CHRY, York University's campus station.
A short distance further down the band is another station
that I like to listen to, the AVN,
Aboriginal Voices Network. It hit the airwaves in Toronto
at 106.5 MHz in 1999, and their signal sounds very nice
and they give exposure to Three O'clock Train, Mak
Makenzie's band.
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The Scott 312 is one of a small group of Scott solid state
tuners that holds some appeal to collectors. Any nuvistor-equipped
tuner should be of some interest to Scott collectors, so pristine
348's and 344's are to be sought
after. Scott tuners are in their own class when it comes to
performance. The market was theirs in the 1950's and certainly
the company could have maintained its dominance and might possibly
have survived as an organizational unit had it stayed focused
on the carriage trade and avoided the loss-leading receiver
class of item. Consider the parts bin analysis. A 342 receiver,
post front end, had all the same parts as a 312C, plus all of
the associated functions of an integrated amplifier. The only
substantial difference between the 342 and the 312C is found
in its front end and in the level of adjustment that its IF
stage received. There are a lot of dollars in between the two
products in the production bin, but the list prices were of
each were close. This was not the case with the introduction
of the 344, which was, at $429.95 lessed only by the mighty
380, which cost $480.00. In 1964, no less. But within years,
competing with Japanese junk sellers meant running on slight
margins and for Scott this ended up with computer grade modular
boards (built out of phenolic at first) being installed, plug
and play, into aluminum industrial art chassis housing a Garrard
automatic being sold against a plastic molded piece of junk
built around cheesecake circuits with the same crummy Garrard
automatic.
And, should there be humour in the Scott story somewhere, it
is in the certain irony that the tuner that Scott plonked into
its cheapest items had much to do with the 312. The IF would
have corresponded to what you could expect to find in a 341,
but the multiplex adaptor would most probably be identical to
whatever adaptor Scott was using. With one exception, the multiplex
adaptors are all as good as you will find in what I call the
'adjustable' variety. Scott produced several models between
1969 and 1971 that are particularly nice.
Attractive adaptors open to stereo easily, don't flicker between
mono and stereo, and I suppose most importantly, sound correct
with respect to separation. I have only had a few on-air experiences
with channel testing: The most recent was with a 367, which
uses a four transistor multiplex adaptor stage. Listening through
headphones, I could hear with certainty just how good the adaptor
was. I heard barely detectable traces of cross channel 'chatter,'
much consistent with what I should expect, which is almost -40dB,
probably closer to -36dB. I have had hundreds of 'studio' hours
through the headphones that I use, the Sennheiser HD424.
Scott designed a circuit to give its multiplex adaptor the
qualities that I described. They called the circuit 'comparatron
automatic stereo' and it made it possible to use the 312 as
a rebroadcast or a record monitor to maximum advantage by allowing
the tuner to pass a stereo signal as much of the time as possible,
and by switching seamlessly to mono, provide acceptable noise
free performance at those moments when the signal becomes diminished.
Plenty of tuners are being made today that fail horribly at
what the 312 does so well. Even chip locked tuners have nasty
transient problems, don't know when to switch, etc. What a mess
FM is. Not with the 312 and other Scott equipped circuits.
Scott rated the 312 at 2.0 uv sensitivity across the band.
That's not as good as the 4312, 4310,
or 310E at 1.9 uv across the band,
but I expect that there are a few radio technicians who peaked
these tuners to give improved performance over a small band
of frequencies. It's possible to get extremely good low sensitivity
numbers, say 1.7 uv at one spot, by sacrificing performance
across the overall band. It's not something to be tried at home.
With the arrival of the 312D, scott
offered broadcasters a guaranteed 1.7 uv. The 312D, a transitionary
model, was the last of its box dimension from Scott. Its penultimate
tuner, the 431, occupied the chassis size of a 433.
ed.
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