Marantz Model 115B

Commentary

AM/FM tuner with traditional gyro-touch tuning.

The muting circuit consists of a noise amplifier with two transistors and a switching circuit with two transistors and one FET. It employs a method of controlling by three types of inputs.
The first is based on the signal strength, the second is based on the state of noise in the detector, and the third is based on the DC component of the detection output. The combination of these three factors not only eliminates inter-station noise but also eliminates unwanted signals generated in the tuning range.

The FM front-end section uses a double-tune system with a four row varicon and two stage FET configuration.

The IF amplifier consists of six transistors and six elements of a phase-linear filter.

A multi-stage symmetrical limiter circuit consisting of a hot-carrier diode and transistor is mounted for the limiter, and the dynamic aperture is very narrow, thereby eliminating unnecessary components such as AM modulation components.

A PLL type IC is used in the MPX section.
If you have an automatic stereo / monaural switching circuit that checks the input signal and can guarantee the stereo quality, the stereo demodulator will automatically operate and the stereo lamp will light.
If the input signal is not strong enough, it is automatically converted to a monaural signal.

Equipped with a monaural switch.

It is equipped with a high-blend switch that suppresses the negative phase noise for weak FM signals with extreme noise or interference.

An attenuator switch is mounted. When turned IN, the signal is attenuated by approximately 20 dB and added to the antenna coil.

It is equipped with the QUADRADIAL OUTPUT connector for 4-channel broadcasting.

The transformer, FM front end, AM tuner section and supplies are covered in black to prevent unwanted radiation.

The AM tuner section consists of an integrated circuit that contains an RF-amplifier, Local Osillator Mixer, IF amplifier, detector circuit and amplifier for signal strength indicator in one package, and a transistor that amplifies the detected audio signal.
The RF amplifier is equipped with two tuning circuits using a 3-row varicon.

Model Rating

Type	FM/AM Tuner
FM Tuner Section
Tuning frequency range	76 MHz to 90 MHz
Practical sensitivity (IHF)	2.3 μ V
Chinese arrowhead エティング Slope	5 μ V : 53 dB 10 μ V : 57 dB 50 μ V : 70 dB
IF interference ratio	96dB
Image interference ratio	70dB
Spurious interference ratio	96dB
AM suppression ratio	60dB
Selectivity (IHF)	60dB
Capture ratio	1.6dB
Signal-to-noise ratio	70dB
Stereo separation	42dB(1kHz)
Harmonic distortion factor	mono:0.15% stereo:0.3%
Frequency response (50 μ sec, de-emphasis)	± 1 dB (50 Hz to 15 kHz)
<AM Tuner Section>
Tuning frequency characteristic	535 kHz to 1605 kHz
Practical sensitivity	20 μ V
Selectivity	26dB
Image interference ratio	70dB(1400kHz)
Signal-to-noise ratio	46dB
<General>
Pwer	100 VAC, 50Hz/60Hz
Power consumption	25W
External dimensions	Width 390x Height 146x Depth 300 mm
Weight	Body : 8 kg Packing Weight : 13.6 kg