Eico HF 87 Owners Manual

Page 2

MODEL HF 87 STEREO DUAL POWER AMPLIFIER

general description

GENERAL

The HF87 is adual power amplifier for stereo use with the
superb HF85stereo preamp or any good self-powered stereo
preamp. Each power amplifier is conservatively rated at
35 watts. They employ our thoroughly proven cathode-
coupleci phase inverter circuit, preceded by adirect cou-
pled voltage amplifier. The output stage employs ultra-
linear connected, self-biased, push pull EL-34's.

The two amplifiers may be operated in parallel to deliver
70 watts for non-stereo use; either input can be made
common for both amplifiers by a service selector switch.
Other convenience features include a level control at each
input, on a-c power switch, two convenience outlets, and
a fuse in an extractor post mounting.

The common power supply for the two amplifiers exhibits
very good regulation because of the self-bias operation and
the very low impedance characteristic of silicon diode
rectifiers. As a result, signal conditions in one amplifier
have negligible effecton the operating conditions of the
other amplifier - a worthwhile obiective in ahigh quality
design. To insure long life for the silicon diode recti-
fiers, electrolytics and tubes, a Surgistor is employed to
limit the starting surge currents.

SPECIFICATIONS

Output Power: 70 watts (two 35 watt amplifiers) contin-
uous, i40 watts peak

lM Distortion (60 6. 7000 CE at 4:1): 1% at 70 watts

Harmonic Distortion: Less than let: from 20 to 20, 000 cps
within 1 db of 70 watts

Freguency Resanse: i=0. 5 db 5 cps - i00kc

Transient Res onse: Excellent square wave reproduction
l3 usec rise timel; negligible ringing, rapid setting on
20kc square wave

inverse Feedback: 17 db

Stability Margin: i7 db
Damping Factor: Above ii, 20 cps to 20kc

The intrinsic quality of the driving circuit, the output
tubes and the output transformers is so high that less feed-
back than usual is required to obtain extremely low dis-
tortion figures. As a result, the amplifiers have high
margins of stability.

Other important design features, characteristic of all ElCO
amplifiers, are a rugged and generous chassis, maximum
separation of power tubes from each other and heat-sen-
sitive components, trouble-free-point-to point wiring,
and painstaking attention in reducing distortion without
compromising stability. Filter electrolytics and rectifiers
operate well below maximum ratings to insure long life.

The HF-87 has been designed to maintain its excellent
characteristics underspeaker load (including electrostatic
types) as well as the resistive load normally used for test-
ing. Phase corrections have been provided at both ex-
tremes of the mdio spectrum to insure stability under all
conceivable conditions and to insure that variations in
components and construction will not affect the perform-
ance. Stability is maintained on all speaker tops with
loads ranging from zero to infinity. Overload character-
istics are excellent. The HF-87 will not exhibit bounce
or flutter under pulsed conditions.

Sensitivity: 0. 38V for 70W output
Channel Separation: 55 db
Hum: Better than 90 db below rated output

Speaker connections: 4, 8, l6, and 32 ohms

Controls: Level Ch. 1, Level Ch. 2, "Service Selector"

switch, ON-OFF switch

Tubes: i-ECC83/1MX7, 2-6SN7GTB, 4-EL34, 2-silicon
diode rectifiers protected by a Surgistor

Power Source: 117V, 60c
Power Consumption: 2 i5 watts; 5 amp. fuse

Size: HWD - 6" x 15" x H"

Shipping Weight: 32 lbs.

COWIIGHT© 1959 ELECTIONIC tNSIRUMENT COMPANY, Inc.