Pilot 248 integrated stereo amplifier
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Taken from High Fidelity Magazine August 1961

AT A GLANCE: The Pilot 248 is a high quality integrated stereo amplifier which combines the dual 30-watt power amplifier channels of the Pilot 264 with a comprehensive stereo control facility. The result is an attractive, relatively compact, and generally fine performing instrument. Price: $249.50 (includes enclosure).

IN DETAIL: The control functions of the Pilot 248 were found to be complete, if conventional. For instance, the tone controls are the concentric, slip-clutch type, which means they can be used on both channels simultaneously, or—by a slight movement of the control on its shaft—adjusted for each channel individually. Master volume and stereo balance controls are included. A separate switch offers two degrees of loudness compensation, or none at all. Seven pairs of stereo inputs are provided (or fourteen for mono signals) which are chosen by the selector switch. These include: FM-AM tuner, multiplex adapter, tape recorder, tape head, microphone, and phono. A mode selector chooses stereo, stereo reverse, or either channel playing through both speakers. Handily arranged slide switches control power, rumble filter, scratch filter, tape monitor, and a selection of either of two phono inputs. The speaker terminals, in addition to the normal two (stereo) speaker connections, include provision for connecting a "center channel" speaker as well. This speaker, which delivers a mono signal from stereo inputs, can be used for "center fill" on stereo, or for mono listening remotely. A speaker selector switch chooses either or both of the two (left and right) speakers connected. The Model 248 measures 14½ in. across, 12¾ in. deep, and 5¼ in. high. It is supplied in a metal housing and finished in the brass and black styling that characterizes Pilot's recent products.

Laboratory tests indicate that the Model 248 is truly a high quality amplifier. At normal listening levels, its IM distortion was virtually immeasurable (below 0.1%); it reached 2% only at 38 watts output per channel. This is a higher power output than the amplifier is rated at; the IM figure, incidentally, was derived with both channels driven to full power simultaneously, a most severe test. Mid-frequency harmonic distortion also was well below 0.1% at normal listening levels (though this is not shown in the curves). Actually, the critical test of harmonic distortion at 20 cycles shows the true mettle of the amplifier. This figure was well under 0.3% up to 15 watts output, and reached 2% at 21.5 watts per channel.

The frequency response curve, taken at a low output level, was generally good. Power response, taken at 35 watts, was nearly as flat. The action of the tone controls was good, as was the phono equalization curve, which showed only a slight error for RIAA compensation. The effect of the loudness control can be mild or strong, as selected by the user. The rumble and scratch filters, however, were found to be too gradual in their action, removing appreciable program material along with the noise content at low and high frequencies respectively.

A somewhat novel feature of the Model 248 is the individual "certified performance data" sheet that accompanies each model and shows the manufacturer's measured distortion and output for the particular unit. It is interesting to note the extent to which this data was verified in our laboratory tests. For instance, the amount of harmonic distortion when plotted against frequency response, from 25 to 20,000 cps, agreed almost exactly with our test data. Power output at 20 cps, at 0.5% distortion, was not quite as high as claimed, but the difference was slight enough to be characterized validly as not far from the limits of experimental error. The IM distortion figures given for 30 watts output could not be matched in our lab tests. Actually, the measured IM distortion varied widely with different settings of the amplifier's volume control. At that, the variation, with respect to the claimed figures, hovered around an order of a few tenths of a per cent. Thus, instead of the 0.15% claimed, it was found to be approximately 0.2% to 0.5%, figures which—on any basis, comparison or no—stack up as very good.

In sum, the Pilot Model 248 can be characterized as one of the better integrated amplifiers presently available. It represents an attractive combination of high power, low distortion, high gain, and very low hum (for normal gain settings). These performance characteristics, combined with the obvious convenience of its functions all on one chassis and the simplified installation it suggests, should recommend it to many buyers.