Scott 350B
A time-division multiplex circuit, a tone instead of a light, and the most comfortable tuning knob in FM.
Overview
The 350B is a stereo FM tuner built for the listener who wants the station to sound like the station, not like the receiver.
The 350B is a refinement, not a reinvention. The 350 series dates to the advent of FM stereo, and the original was among the first stereo tuners with a built-in multiplex adapter. By the time the B arrived, Scott had improved sensitivity by roughly ten percent and added a way to tell whether a broadcast was actually in stereo. Two years on, the magazine noted, the entire circuit was time-tested.
The stereo indicator is what separates this tuner from its peers. There is no light. You switch to the "monitor" position and dial across the band, and if a stereo broadcast is present, you hear a tone. Scott called it the Sonic Monitor. HiFi-Stereo (February 1963, p.61) noted that a tone is slightly less convenient than a visual indicator - you have to throw a switch to check - but it has a real advantage. Stereo separation depends critically on tuning, and visual indicators are typically of little help there.
The front panel also carries a tape output jack. It lets you record off the air with a portable machine or a deck that isn't wired into the system, without pulling the tuner out to reach the rear-panel jacks.
Under the hood, the 350B uses the well-known Scott front end, three IF stages, and a wideband ratio detector. The limiter is a conventional pentode. The original non-letter 350 had used a 6BN6 gated-beam limiter, a design that didn't last, and the 350B reverted to the traditional pentode. In the balanced ratio detector, the junction of the two resistors is grounded and the output is taken from the tertiary winding. The circuit is essentially the same configuration Scott used in the mono 314 tuner, with dual audio sections and special filters added to handle the noise problems peculiar to multiplex reception.
You get a simple tuning meter instead of a super-sensitive one, and pots for output level instead of calibrated attenuators and VU meters. Reception isn't compromised. The same review reported the tuner pulled in a large number of stations without distortion and with excellent signal-to-noise, and that it did not drift even without the features that usually prevent drift.
Scott's own advertising claimed 2.2 µv IHFM and called that figure conservative, asserting that independent tests showed the 350B delivering better sensitivity still. HiFi-Stereo (February 1963, p.61) measured capture ratio at 4.2 db, output at 2.1 volts, frequency response within ±0.5 db from 50 to 15,000 cps, and separation of about 27 db over most of the range, falling to 18.5 db at 10,000 cps and 11 db at 15,000 cps. The subchannel filter, when engaged, cut separation to roughly 5 to 7 db above 5,000 cps. Those separation figures are the limitation of the design: wide open in the midband, narrowing at the top, and narrower still with the filter in.
Collectors note that the 350B is fairly common as Scott separates go, which makes it one of the more approachable tuners in the line rather than a trophy piece. One caveat from the service literature: if the IF circuit is misaligned or not working correctly, the tuner will show odd gain problems, distorting on strong stations or failing to receive weak ones.
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