Eico HF 52 Owners Manual

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ElECTRONIC INSTRUMENT 60., INC.
84 Wi'hers Si. ' Brooklyn 1, N. Y.

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general description

MODEL HF 52
50 WATT INTEGRATED

HIGH FIDELITY AMPLIFIER

GENERAL

The Model HF52 is the least expensive means of achiev-
ing the highest audio quality, resulting from high power
obtained withoutdistortion throughout the full audio spec-
trum, virtually absolute stability, and flawless transient
response. Despite the fact that the preamplifier-control
section is placed on the same chassis with a high power
amplifier, engineering of the layout has eliminated any

FEATURES

1 . Extremely low distortion preamplifier-equalizer cir-
cuit, equalizing entirely by feedback. Selection from five
equalizations permits correct compensation for practically
any microgroove or 78 rpm recording.

2. Extremelylaw distortion printed circuit feedback bass
and treble tone controls. These controls do not affect
the volume or interact with each other, and also providea
true "flat" position. Turnover frequency in both bass and
treble varies with the degree of boost or cut, making it
possible to bring up the extreme lows or extreme highs
affecting the mid-range as well.

3. DC superimposed on all tube filaments to eliminate
cathode-heater leakage as a source of hum.

4. A Centralab printed-circuit, prewired loudness control
(Compentrol) plus a separate level control, both on the
front panel, permits an infiniteselection ofloudness"con-
tours" at any desired listening level. By pro-setting the
panel level control as instructed, theloudness contrclwil'l
automatically provide correct Fletcher-Munson loudness
compensation at the setting which gives the desired listen-
ing level.

5. Four high level and two low-level inputs enable this
amplifier to accomodate iv, tape recorder, AMFM tuner
(or separate AM and FM tuners), ceramic or crystal cart-
ridge, as well as any leading magnetic or FM phono pick-
upwithout thenecessity of component changes. No cross-
talk; selector switch grounds all inputs but one selected.

6 . Low impedance cathode fol lower tape-output unaffect-
ed by any controls.

undesirable couplings. The hum and noise level achieved
is on a par with that of well-designed lower power inter-
grated amplifiers and will be found entirely satisfactory
even by critical listeners. The output stage and the out-
put transformer, the type of power amplifier circuit, and
the power supply components are identical to that used in
the Model HF5O power amplifier.

7. The use of a cathode follower at the high level inputs
makes it possibleto provide the high input impedance re-
quired for flat frequency response and high output from the
new, high quality, self-equalizing ceramic cartridges.

8. The output of the preamplifier-control section and the
input to the power amplifier section have been brought out
to separate receptacles on the rear chassis apron for the use
of peoplewhowish to employ an electronic cross-over net-
work and an additional amplifier (or amplifiers).

9. The level control is placed at a low-impedance point
in the amplifier (after the tone controls)so that the square
wave response is unaffected by the level setting. This is
possible because the cathode follower input circuitwill
not distort the signal even at peak signal voltages for in
excessof the value ofsignal that will develop rated output
power. Another benefit of this arrangement is a high sig-
nal-to-noise ratio in the tone control stage.

IO. The poweramplifier features a cathode-coupled phase
inverter, which provides drive for the output stage from
equal and comparatively low impedances and direct coupl-
ing from the preceding first voltage amplifier stage. The
importance of the cathode-coupled phase inverter is that
it provides forced balance over the entire frequency and
dynamic range.

ii. EL34/6CA7output pentodesin a push-pull Ultra-Lin-

ear output stage operating with fixed bias.

12. Extremely high qualityoutput transformer, employing
grain-oriented steel , extensively interleaved windings,and
fully potted in a seamless steel case. 4, B, and lb ohm
speaker connections are provided. (*Ch'icago Standard)