You can register with hifiengine.com andfind it and the service manual.
There really isn't a lot to a power amp to be operated. This one differs from most in that it has an input level control and VU meters.
From
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Dynamic 150 + 150 Watts Power Output, Generous High-power Design
The Spec-4 employs DC construction which excludes capacitors from the NFB circuits and uses a dual transistor differential amplifier with a current mirror circuit in the 1st stage. This provides a stable operation and also high gain over a wide frequency range. The pre-driver stage is a class A amplifier circuit with a regulated current circuit for the load. This makes for high-gain amplification with superior linearity. Furthermore, there is an overdrive limiter and power limiter circuit which is designed to protect the power transistors and make for added reliability.
The power stage employs a 3-stage Darlington pure complementary parallel SEPP circuit.
The SPEC-4 delivers
Continuous Power Output of 150 watts per channel, min. RMS, at 8 ohms from 20 Hertz to 20,000 Hertz with no more than 0.01% total harmonic distortion.
Completely Independent and Perfectly Stable Left / Right Power Supplies
The mighty power supplies are completely separated for the left and right channels. Also, each channel is provided with two 22,000uF large-capacity electrolytic capacitors and large transistors with a superior regulation. They achieve outstanding channel separation and a clear, powerful reproduced sound, in addition to the wide frequency response. There is a built-in surge killer circuit to suppress inrush currents from the power transformers and high currents which charge the electrolytic capacitors. This circuit ensures that none of the parts are affected by these adverse currents.
Protective Circuits Composed of Fast-response Relays and Electronic Circuits
Each channel is protected by a DC and over current detection relay circuit. In the event of the speaker terminal shorting due to poor connections or when DC current is generated in the output, the output circuit is immediately disengaged and the speakers and transistors are safeguarded against any possible damage. The protective circuits also function as muting circuits when the power switch is turned on and off.
Peak Level Meters with Outstanding Waveform Response
This power amplifier incorporates logarithmic compression peak meters with a wide scale (-40 -+3dB). With 8-ohm speakers, they allow the output to be read out from 0.01W to 300W. Moreover, the meters feature a fast response for peak signal indication. In addition to the peak output reading, it is easy to interpret the dynamic margin with respect to the SPEC-4’s clipping level.
Input Level Controls with dB Calibration
The SPEC-4 is equipped with input level controls with direct readout attenuation values (-dB). These can be used to continuously adjust the input levels for each channel in accordance with the rated output voltage of the preamplifier. In this way, the SPEC-4 can perform the proper gain control according to the preamplifier’s output level. The preamplifier will thus be used in the condition possible for the best S-N ratio and distortion characteristics.
Stylishly Professional Front Panel Design
Just as you would expect from a sophisticated system, the SPEC-4’s front panel is professionally designed with the large level meters in the center. Also. The front panel’s dimensions allow the model to be mounted in an EIA standard rack, just like real professional-use amplifiers.
SPECIFICATIONS
ICs………………………………........................................2
Transistors………………………………...........................61
Diodes……………………………….................................62
Power Amplifier
Circuitry………………………………Current mirror loaded differential Amplifier
3 stage darlington parallel push-pull
Direct-coupled OCL. (DC amplifier construction)
Continuous Power Output of 150 watts * per channel, min. RMS, at 8 ohms from 20 Hertz to 20,000 Hertz with no more than 0.01% total harmonic distortion, or 180 watts per channel at 4 ohms from 20 Hertz to 20,000 Hertz with no more than 0.03% total harmonic distortion.
Total Harmonic Distortion (20 Hertz to 20,000 Hertz, 8 ohms)
Continuous rated power output………………………………................................0.01%
75 watts per channel power output……………………………….......................... 0.01%
1 watt per channel power output……………………………….............................0.01%
Intermodulation Distortion (50 Hertz to 7,000 Hertz = 4:1, 8 ohms)
Continuous rated power output………………………………................................0.01%
75 watts per channel power output……………………………….........................0.005%
1 watt per channel power output………………………………........................... 0.005%
Frequency Response………………………………...............5 Hertz to 100 kHertz
+0/1 dB
Input (Sensitivity / impedance)……………………………............................1V/50k ohms
Output
Speaker……………………………….................................................4 ohms to 16 ohms
Damping Factor (20 Hertz to 20,000 Hertz, 8 ohms……………………………….........100
Hum and Noise (IHF, short circuited, A network………………………………........11 5dB
Miscellaneous
Power Requirements………………………………...................................AC 120V 60 Hertz
Power Consumption………………………………..........................................760 watts (UL)
Dimensions………………………………..............................480(W) x 187(H) x 445 (D)mm
18-7/8 x 7-3/8 x 17-7/16 in.
If you have the unit disassembled and have a voltmeter test on the Caps. then just trace along the wiring or traces; to the next part. This is usually a large power resistor.
Al
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