Marantz Model 20B

Name: Marantz Model 20B
Brand: Marantz

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layout: technical-manual/model.njk

title: Marantz Model 20B

brand: "Marantz"

model: Model 20B

category: Tuner

years: 1965-1967

tags: [tuner, tube, fm, marantz, separate]

Marantz Model 20B

The Marantz Model 20B is a high-performance FM-only tuner introduced in 1965 as part of the company's professional-grade "separates" line. It was designed to be paired with the Model 15 power amplifier, sharing its distinctive blue-backlit meter and chassis styling for a matched system appearance. The 20B succeeded the earlier Model 10B tuner, offering a more commercially viable design by utilizing a superheterodyne circuit instead of the 10B's complex and costly heterodyne design, while still targeting the high-end market.

This tuner is characterized by its sophisticated tuning mechanism, which employs a dual concentric shaft for the main tuning capacitor. The outer shaft controls the primary tuning via a precision 4-gang capacitor, while the inner shaft operates a proprietary "M-X" (Multiplex) filter for noise reduction. Its circuitry is entirely tube-based, utilizing 13 tubes including two 6AU6s in the IF stage and a 6CG8/6FQ7 as the ratio detector for FM demodulation.

Specifications

Specification	Detail
Type	FM Superheterodyne Tuner
Frequency Range	88 MHz to 108 MHz
Tubes	13 total (6CG8, 6AU6 x2, 6U8, 6BH6, 6EA8, 6DT6, 6DR7, 12AT7 x2, 6AQ5, 0A2)
IF Stages	3 stages, 10.7 MHz
Usable Sensitivity	2.5 µV (IHF)
Capture Ratio	3.0 dB
Selectivity	40 dB (alternate channel)
Audio Output	2.5 V RMS (100% modulation)
Output Impedance	10 kΩ (High), 600 Ω (Low)
Harmonic Distortion	0.8% (mono)
Semiconductors	4 silicon diodes (in power supply)
Power Consumption	65 Watts
Dimensions (W x H x D)	16-1/8" x 5-1/8" x 13-3/4"
Weight	28 lbs (12.7 kg)

Historical Context

Produced from 1965 until approximately 1967, the Model 20B was introduced during the peak of the tube era and the rise of high-fidelity FM broadcasting. Its significance lies in its position as a no-compromise tuner designed to extract maximum performance from the FM band, bridging the gap between the legendary, ultra-expensive Model 10B and the more consumer-oriented models. It represented Marantz's commitment to the high-end separate components market shortly before the company's acquisition by Superscope in 1966, which would shift its focus towards integrated receivers.

Design Features

The technical highlights of the Model 20B center on its tuning system and filtering. The dual concentric tuning shaft provides both main station tuning and adjustment of the proprietary "M-X" notch filter, designed to reduce high-frequency noise and interference from multiplex stereo signals. The front panel features a large, blue-backlit tuning meter that indicates signal strength and center-of-channel tuning. The chassis is constructed on a heavy-gauge steel frame, with critical audio stages shielded in aluminum cages to prevent interference. Its power supply uses a solid-state silicon diode rectifier for improved reliability over tube rectifiers.

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