Vintage Hi-Fi Audio Restorations: D.Schuelke's Marantz 2600 Legendary Receiver Restoration

Marantz 2600 Legendary Stereophonic Receiver

The Marantz 2600 was the largest receiver produced for the era by Marantz and their response to the Monster series seen by Pioneer/Sansui at the time. The 2600 uniquely shares a lot of design concepts and chassis/build points as the Marantz 2385 and closer yet 2500 series as the these employed a Hitachi scope as well. Advanced RF features such as quartz lock/sensor touch were employed as well. A massive Toroidal transformer give a huge bulk to these receivers though proper maintenance is required to prevent damage to these, especially concerning the soft start.

P800 Power Supply

The 2600 regulated power supply is broken down for the regulated -/+13 & -/+ 31V output via a series of separate full wave rectifiers like many Marantz P800 designs. Due to the Scope display a two fused high voltage 180/570V outputs were implemented.

The three regulators were replaced with modern, robust TO-220 type MJ OnSemi devices with better dissipation handling and new MICA insulators with full synthetic Wakefield thermal compound applied. All remaining small signal devices were replaced with modern, low noise TO-92/TO-92L with better dissipation handling. Onboard diodes and zener diodes were replaced with modern Vishay axial type. Common cathode/anode rectifiers were replaced with a state-of-the-art ultra fast, soft recovery MUR series TO-220 type devices. The voltage adjustment was replaced with a precision Bourns sealed potentiometer.

All of the electrolytic capacitors were replaced with a low impedance, high temp (105C) Nichicon type with an increase in operating voltages, several of the DC coupling capacitor MFD ratings were increased for better noise reduction and smoothing. Original films were all replaced with high grade WIMA polypropylene type including the common mode rectifier bypass films.

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AFTER

-/+31V & 13V Confirmations

Soft Start Modification

A very common failure mode on the 2500/2600 series is the soft start current limiting array. To avoid future faults the wire-wound type are replaced with a high quality ceramic/enamel Ohmite 10 and 25Watt resistors with new bracketing installed. A new Tyco KUP-48 style soft start relay installed as well.

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AFTER

PN01 Audio Muting / Protection

As part of the multi-protection designs in the 2600 the PN01 has a muting on off application as well as speaker shunting in the case of excessive DC deviation at the output.

The relay was replaced with a modern Omron MY series 48V relay. The R/C timing capacitor was replaced with a low impedance, high temp (105C) Nichicon PW capacitor with an increase in operating voltage. The small signal device was replaced with a modern Fairchild TO92L type with better dissipation handling and a new axial Vishay ultra-fast, soft recovery UF series diode.

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P900 Scope Control

One of the sought after features on the 2500/2600 is the addition of the CRT Hitachi 50TB31 type output tube display. Often times faults are assumed to the tube when in reality the Jfet 2SK’s or Regulators are at fault.

All of the bypass films here were replaced with a Nichicon polypropylene type and high grade WIMA polypropylene film. New Regulators coupled and installed along with all new precision, sealed Bourns potentiometers.

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PX01 Peak Indicator

As I’ve noted in other 2500/2600 restorations I’ve published the peak indicator design is quite accurate in this units allowing for a variance in load applications while still maintaining accuracy.

All of the electrolytic capacitors here were replaced with a low impedance, high temp (105C) Nichicon PW type with an increase in operating voltages. All new small signal Fairchild TO92 devices and new TO-126 Fairchild devices were installed. All diodes and zener were updated with modern axial Vishay type including the MV varistor types.

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P400 RIAA (Phono)

While being on the most difficult assemblies to access and service due to a shoe-horned form factor the 2500/2600 phono stages are incredibly accurate. Employing a Class A emitter/output stage.

The input differential devices were matched with 3% and installed in pairs with new low noise TO92 Fairchild devices. All of the capacitors were replaced with a audio grade KT/KA Nichicon and low impedance PW particularly for the DC coupling stages, all with an increase in operating voltages.

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PE01 Tone Amp / PT01 Tone Stage & PS01 Tape/Monitor

The front end audio stage of the 2500/2600 series is a very large assembly broken down to the audio flat amp and tone stages. These assemblies are mounted directly to front chassis and form to a perpendicular mount.

PE01

The flat amp stage is unique in Marantz designs as it employs four total TA7136 “pre-amplifier” IC”s, two per stage input/output. The only difference between the 2500 and 2600 is the addition of a rail DC decoupling capacitor.

All of the electrolytic capacitors here were replaced with a audio grade KT/KA Nichicon type and low impedance Nichicon PWs with an increase in MFD filtering value, including increases in operating voltages. Remaining 1MFD> and applicable mylar capacitors were replaced with a high grade WIMA polypropylene film capacitors

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AFTER

Many of the soldered potentiometers need to be removed for a proper cleaning and lubrication

PT01

As describe, this assembly mounts perpendicular to the PE01 board. The differential for here are 2SK JFET devices as opposed to NPN’s standards.

All of the small signal devices were replaced with modern, low noise Fairchild devices. Electrolytic capacitors were all replaced with a low impedance Nichicon PW type with an increase in operating voltages. Remaining small value and mylar capacitors were replaced with a high grade WIMA polypropylene film capacitors.

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AFTER

PS01 Tape/Monitor Relay

The few capacitors on this assembly were replaced with a low impedance Nichicon PW type and high grade WIMA polypropylene film capacitors.

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P700 Drivers

The form factor of the P700 driver stage is one of the concepts that sets the 2500/2600 apart, and especially from their similar 2385 counterpart. These series use a tunnel design on U-shaped heatsink coupled together, with a sealed fan output and skipped TO-3 output device heatsink in a effort to reduce and expel radiant heat. The biasing scheme is tied to two lo/hi thermostats on the heatsinks for additional protection.

The P700 utilizes a fully complimentary/symmetric “quadruple paroled direct coupled circuit” The NPN differentials were matched within 1% and thermally coupled together in pairs using low noise TO92 Fairchild devices. Remaining Pre-drivers and gain stage devices were all replaced with modern TO126/TO92L low noise Fairchild devices. New driver stage TO-220 OnSemi devices were installed on the heatsink planes. New precision, sealed Bourns adjustments installed. All zener and diodes including MV type were replaced with modern axial Vishay type.

Matched Differential Mapping

All of the capacitors were replaced with a audio grade KT/KA Nichicon and low impedance Nichicon PW type with an increase in operating voltages. All of the films on this assembly were upgraded to a high grade WIMA polypropylene type.

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Bias Confirmation

P200 Main RF / PK51 Touch Sensor & PC01 FM Buffer / PC50 Quartz Lock

For both AM/FM Front end assembly and the associated gyro touch feature all of the electrolytic capacitors including tantalum capacitors were replaced with a low impedance Nichicon PW type with an increase in operating voltages and a high grade, precision WIMA polypropylene series film capacitors

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PC01 / PC50

Similar to the above assemblies all of the capacitors were replaced with a low impedance Nichicon PW type with an increase in operating voltage and a high grade, precision WIMA polypropylene series film capacitors.

PC50