McIntosh MC275
Expert Tube Amplifier Restoration & Repair

About My Tube Amplifier Service

I'm the owner and lead technician at Tek Media Group, and I've been restoring McIntosh tube amplifiers since 1994. The MC275 is one of the most iconic amplifiers ever built – and it deserves expert care. Over the years, I've rebuilt hundreds of MC275s for audiophiles, collectors, and studios across Southern California. My approach is thorough: I rebuild power supplies, replace aged capacitors, bias output tubes to factory specifications, and verify performance on precision test equipment.

Restoration Services I Offer

Detailed Repair Information – From My Workbench

• Multi-Section Can Capacitors: Original capacitors dry out and leak – I rebuild or replace with high-quality modern equivalents
• Main Filter Caps (C1, C2, C3): 100µF/450V – I replace with 105°C rated, high-ripple current types
• Selenium Rectifier: Original selenium rectifiers are failure-prone and smell terrible when they fail – I replace with silicon diode assemblies
• Voltage-Dropping Resistors: I check and replace drifted power supply resistors
• B+ Voltage Verification: I verify proper plate voltage (typically 450V) after restoration

• Bias Adjustment Pots: Original pots can become intermittent – I clean or replace as needed
• Bias Resistors: I replace drifted cathode resistors with 1% precision metal film types
• Output Tubes (KT88/6550): I test all tubes on calibrated tube tester and match quads for balanced performance
• Driver Tubes (12AX7, 12AT7, 12AU7): I test and replace weak or noisy tubes
• Bias Adjustment Procedure: I set bias per factory specifications (typically 50-55mA per tube) and verify stability

• Carbon Composition Resistors: Original carbon comp resistors drift in value over time – I test and replace out-of-spec units
• Screen Grid Resistors: Common failure point – I replace with flameproof types for safety
• Plate Load Resistors: I check and replace noisy or drifted resistors
• Tube Sockets: I clean and tighten all tube sockets for reliable contact
• Controls & Switches: I clean input selector, bias test switches, and all controls with DeOxit

• Grounded Power Cord: I install a 3-prong grounded power cord for safety (original two-prong cords are unsafe)
• Safety Capacitors: I replace "death caps" with modern X1/Y2 safety capacitors
• Fuse Holder: I verify proper fuse rating and holder condition
• AC Line Filter: I can add EMI/RFI filtering upon request

Common Problems I Solve

#1 Power Supply Capacitor Failure

Symptom: Excessive hum, low output power, overheating, intermittent operation.
My Solution: I replace all electrolytic capacitors in the power supply, including multi-section cans. This restores proper filtering and eliminates hum.

#2 Leaky Coupling Capacitors

Symptom: Distortion, red-plating output tubes, instability, poor sound quality.
My Solution: I replace all coupling capacitors with high-quality modern film capacitors. This restores proper bias to the output tubes and improves sound quality dramatically.

#3 Drifted Resistors

Symptom: Off-spec voltages, imbalance between channels, poor bias stability.
My Solution: I test every resistor in the amplifier and replace any that have drifted more than 10% from nominal value.

#4 Tube Failure & Bias Drift

Symptom: Weak output, distortion, one tube glowing red, channel imbalance.
My Solution: I test all tubes, replace weak or mismatched tubes, and adjust bias to factory specifications.

#5 Selenium Rectifier Failure

Symptom: Low bias voltage, bias instability, burning smell.
My Solution: I replace the selenium rectifier with a modern silicon diode assembly with dropping resistor to maintain correct bias voltage.

#6 Screen Grid Resistor Failure

Symptom: Low output, distortion, one channel dead.
My Solution: I replace screen grid resistors with flameproof types and verify output tube screen voltage.

#7 Tube Socket Corrosion

Symptom: Intermittent operation, crackling, tube not heating.
My Solution: I clean and tighten all tube sockets. I replace any damaged sockets.

#8 Noise & Hum Issues

Symptom: Background hum, hiss, crackling.
My Solution: I systematically identify noise sources: power supply, tube noise, resistor noise, or external interference. I replace noisy tubes and components.

MC275 Versions – I Service All

My Restoration Process

Capacitor Replacement Database

Tube Complement & Recommendations

Performance Specifications (After Restoration)

Frequently Asked Questions

My Service Area – Southern California

I serve Los Angeles County, Orange County, Ventura County, Riverside County, San Bernardino County, and surrounding areas. Local pickup and delivery available.