DISCLAIMER: This information is provided for educational purposes only. While we strive for accuracy, we cannot guarantee all information is correct or complete. Always consult official Revox documentation when available. Proceed at your own risk.
⚠️ IMMEDIATE SAFETY WARNING: The Revox G36 contains highly toxic selenium rectifiers that can fail catastrophically, emitting foul-smelling and dangerous fumes. It also contains early paper capacitors and motor run capacitors that WILL fail. Never apply mains power to an unrestored G36 without first replacing selenium rectifiers and critical capacitors.
Overview
The Revox G36 represents the pinnacle and final chapter of tube-based tape recorder development. Produced from approximately 1963 to 1967, it was the last tube recorder Revox released before transitioning to the solid-state A77. The G36 was used by many famous groups in the 1960s including The Rolling Stones, The Beatles, The Kinks, and The Who.
📌 Key Innovations: First Revox to accept 10.5" (26.5cm) reels • Synchronous capstan motor • Optoelectronic tape end sensing (later models) • Tube electronics with Philips Miniwatt valves • Built-in 6W monitor speaker • Mass: 20-22kg depending on version.
Serial number ranges provide important clues about features:
- Up to #36,500: Mechanical microswitch tape end sensor
- #36,501 to #58,000: Feeler-operated gold-plated wire contacts
- #58,001 and above: Optoelectronic tape sensing (light guide through pulley)
Current Market Value (2024)
G36 values have risen significantly as collectors seek the tube sound used on classic 1960s recordings:
Unrestored / Project Unit
Non-working, unknown tube condition, possible selenium rectifier failure
$500-1,000
Partially Restored
Some work done, may need mechanical attention
$1,000-1,800
Fully Restored
Complete electronic and mechanical overhaul, calibration
$2,000-3,500
Mint / Low Hours
Exceptional original condition, all original Philips tubes
$3,500-5,000+
2-Track Studio Version
Professional half-track configuration, most desirable
$4,000-6,000+
Model Description: Each G36 variant offers unique features and value, from basic unrestored units to rare studio versions. Condition, restoration level, and original components significantly affect market price and desirability.
Note: Machines with original Philips Miniwatt tubes in good condition command premium prices. The G36 was also sold under the "Studer Revox" brand, adding collectibility.
Common Failure Modes
#1 Selenium Rectifier Failure (TOXIC)
Symptom: Foul smelling smoke, loss of DC supplies, burning odor. One user reported a 'pfft' noise and wisp of smoke, with solenoid supply completely missing.
Cause: Selenium rectifiers degrade with age and fail catastrophically. They emit highly toxic fumes when failing.
Repair: Replace ALL selenium rectifiers with modern silicon diodes using a specially designed piggy-back PCB. Dropper resistors are required because silicon rectifiers are more efficient and produce higher output voltage.
#2 Motor Run Capacitor Failure (Multiple Variations)
Symptom: Motors run hot, won't start, slow speed, capstan issues. One restorer found a charred capacitor and resistor indicating serious overheating.
Cause: Motor capacitors degrade over 50+ years. The G36 has several variations depending on model, speed, and motor type.
Repair: Replace with new AC-rated motor run capacitors. CRITICAL: You MUST verify your specific configuration:
- Two x 3.0µF (spooling) + one x 2µF (capstan) - early models
- Two x 3.5µF (spooling) + one x 3µF (capstan) - some variants
- Two x 3.5µF (spooling) + one x 2µF + one x 0.5µF (capstan) - later Mk3
#3 Paper Capacitors and "The Charred Resistor"
Symptom: Burned resistors, charred PCBs, smoke. One restorer found a charred resistor and connector board from capacitor failure.
Cause: Early paper capacitors become leaky and short, taking out resistors and causing overheating.
Repair: Replace ALL paper capacitors in the point-to-point wiring. The audio signal path capacitors should be replaced with specially selected low noise, low leakage types.
#4 HT/LT Multi-Section Can Capacitor Failure
Symptom: Hum, poor performance, low B+ voltage, power supply ripple.
Cause: Original electrolytic can capacitors dry out after decades of use and tube heat.
Repair: Replace with custom-made triple can capacitors (450 VDC HT, 63 VDC LT) with increased capacitance for improved smoothing.
#5 Relay and Solenoid Supply Issues
Symptom: Transport won't latch, buttons don't work, missing solenoid voltage. One owner reported solenoid supply completely absent with 25Ω resistance to ground.
Cause: Failed rectifier bridge, shorted relay coils, or open circuit in supply.
Repair: Check rectifier bridge, measure resistance to ground (should not be 25Ω at rest). Replace diodes D1-D4 on pushbutton modules (originally Germanium GES50) with 1N4001.
#6 Capstan Motor Problems
Symptom: Motor doesn't run, noisy, wrong speed, won't switch speeds.
Cause: Speed switch issues, jamming bearings, faulty motor capacitor, open winding.
Repair: From service manual:
- No run: Check speed switch position, replace wafer if defective
- Noisy: Clean bearings, replace capstan assembly if damaged
- Speed too low: Cold machine may need warm-up, check motor capacitor
- Only one speed: Check speed switch contacts
#7 Pinch Roller and Solenoid Issues
Symptom: Pinch roller arm doesn't operate, brakes don't release.
Cause: Dirty solenoid, incorrect remote control dummy plug, dirty contacts.
Repair: Clean and adjust solenoid (section 2.2.3 of manual), clean contacts in push-button assembly (2.2.4), ensure pins 1,2,3 of remote socket are connected.
#8 End of Tape Switch Failure
Symptom: Tape doesn't stop at end, runs into hub.
Cause: Maladjusted switch, defective lamp, blocked light port, incorrectly threaded tape.
Repair: Adjust switch (2.1.5), replace Osram 3644 bulb, clean light port opening carefully. Later optoelectronic versions need photoresistor check.
#9 Tape Counter Belt Failure
Symptom: Counter doesn't move or jerks.
Cause: Original rubber belt turned to goo or snapped.
Repair: Replace counter belt (available in restoration kits).
#10 Tube Issues and Hum
Symptom: Hum, low output, distortion.
Cause: Original tubes may be weak; ECL86 tubes (output) can cause hum if left in circuit with built-in speaker disabled.
Repair: Tube complement: 4x ECC81, 1x ECC82, 5x ECC83, 2x ECL86. Removing ECL86 tubes without changing resistor values increases B+ to unsatisfactory levels - a 5k 5W resistor modification is required.
#11 Voltage Selector and Modern Mains
Symptom: Incorrect voltage operation, potential transformer damage.
Cause: Modern wall voltages (125V) higher than vintage 110V settings.
Repair: Set voltage selector to 130V for modern 125V mains. Options: 110, 130, 150, 220, 240V.
#12 RCA Socket Corrosion
Symptom: Intermittent connections, poor audio, noise.
Cause: Original RCA sockets tarnish and corrode over decades.
Repair: Replace with new RCA sockets (available in restoration kits).
⚠️ CRITICAL: Motor Capacitor Selection Guide
YOU MUST VERIFY YOUR SPECIFIC CONFIGURATION
The G36 had numerous motor capacitor variations depending on model, speed, and motor type. Open your machine and check the capacitors fitted or the printing on the motors.
| Model/Configuration |
Reel Motor Caps |
Capstan Motor Cap |
Notes |
| B36, A36 50Hz |
4.5µF each |
2µF |
Earlier mono models |
| F36, E36, D36, C36 50Hz |
3µF each |
2µF |
Pre-G36 tube models |
| G36 Mk1/Mk2/early Mk3 50Hz |
3µF each |
2µF |
Early production |
| 50Hz machines operating at 60Hz |
2.5µF each |
1.5µF |
Converted machines |
| G36 Mk3 50Hz |
3.5µF each |
2µF + 0.5µF |
Later production |
| G36 Mk3 OEM 60Hz (US market) |
3µF each |
2µF |
Factory 60Hz machines |
| Later Mk3 4/8 pole 50Hz |
3.5µF each |
2µF |
Multi-speed motors |
| 6/12 pole HS motors 50Hz |
3.5µF each |
2µF + 0.5µF |
High speed versions |
🔧 How to Determine Your Configuration: Check the Hz stamped on your reel motors (visible on rotating rotors). Measure capstan shaft diameter (3.0mm for 60Hz, 3.6mm for 50Hz). Note poles stamped on capstan motor. Include your serial number when ordering parts.
Replacement Capacitors: Use Kemet Polypropylene Metalized Film or specially made motor capacitors designed for Revox/Studer machines. Ensure slim 30mm diameter if space constrained.
Systematic Restoration Process
🔧 RESTORATION PHILOSOPHY: The G36 uses point-to-point wiring and terminal boards rather than PCBs. This makes restoration more accessible but requires careful documentation. Work methodically, one section at a time.
"Full Monty" Restoration Checklist (per Nagravox):
✅ Stage 0 - Documentation (photos of all wiring, terminal boards)
✅ Stage 1 - Replace selenium rectifiers with silicon PCB and dropper resistors
✅ Stage 2 - Replace HT/LT triple can capacitors (custom made)
✅ Stage 3 - Replace ALL motor run capacitors (verify values per your model)
✅ Stage 4 - Replace paper capacitors in audio path with low-noise types
✅ Stage 5 - Replace suppression capacitors and rectifiers on switching assembly
✅ Stage 6 - Replace diodes on pushbutton modules (GES50 → 1N4001)
✅ Stage 7 - Motor overhaul: bearings, circlips, correct lubricant (3 motors)
✅ Stage 8 - Pinch roller kit: new roller, PTFE washers, metal shims
✅ Stage 9 - Replace RCA sockets
✅ Stage 10 - Tape counter belt replacement
✅ Stage 11 - VU meter / power / end-of-tape lamps (Osram 3644)
✅ Stage 12 - Update mains lead to IEC socket
✅ Stage 13 - Knob felts, chassis mounting rubbers
✅ Stage 14 - Clean all switches and contacts
✅ Stage 15 - Tube testing and replacement as needed
✅ Stage 16 - Calibration and alignment
One restorer's experience: "It's always interesting what you'll find in old gear, but almost never in a good way. All the caps in this machine will be swapped out while I have this apart anyway, because they are all original and ancient with plenty of tube heating in their past."
Complete Capacitor Replacement Guide
⚠️ CRITICAL - TOXIC - REPLACE IMMEDIATELY
| Component |
Location |
Replacement |
Notes |
| Selenium Rectifiers |
Power supply section |
Silicon diodes on PCB + dropper resistors |
TOXIC when failing - replace before power-up |
⚡ POWER SUPPLY
| Component |
Location |
Replacement |
Notes |
| HT/LT Triple Can Capacitor |
Main power supply |
Custom made 450V HT / 63V LT |
Increased capacitance for better smoothing |
| 600µF Capacitor |
Solenoid supply |
600µF electrolytic |
Check if solenoid supply missing |
🔋 MOTOR RUN CAPACITORS (SEE SELECTION GUIDE ABOVE)
| Component |
Typical Values |
Replacement Notes |
| Reel Motor Capacitors (2x) |
3.0, 3.5, or 4.5µF each |
VERIFY YOUR MODEL |
| Capstan Motor Capacitor |
2µF, 3µF, or 2+0.5µF |
Some models use dual capacitors |
🎛️ AUDIO PATH CAPACITORS
| Type |
Action |
Notes |
| Paper Capacitors |
Replace all |
Use low noise, low leakage types |
| Output Coupling Caps |
Consider increasing value |
Improves bass response with modern preamps |
| C515 (oscillator) |
Check/replace |
Leaky C515 causes recording issues |
🔴 SUPPRESSION AND SWITCHING
| Component |
Action |
Notes |
| Suppression Caps on Switching Assembly |
Replace all |
Often cause smoking and arced contacts |
| Diodes on Pushbutton Modules |
GES50 → 1N4001 |
Germanium diodes should be replaced |
Tube Complement and Replacement
| Tube |
Quantity |
Function |
Notes |
| ECC81 (12AT7) |
4 |
Various stages |
Original Philips Miniwatt desirable |
| ECC82 (12AU7) |
1 |
Output stage |
Check for noise |
| ECC83 (12AX7) |
5 |
Preamp stages |
Critical for audio quality |
| ECL86 (6GW8) |
2 |
Output pentode + triode |
Built-in speaker amp; can cause hum issues |
Tube-Related Modifications:
- Hum reduction: Removing ECL86 tubes requires 5k 5W resistor mod to maintain correct B+
- Weak tube: One owner found NEC 12AD7 (sub for 12AX7) tested weak, replaced with Telefunken 12AX7
- Tube rolling: Original Philips Miniwatt tubes from Holland are considered "Ex Quality" and highly sought
Mechanical Maintenance Guide
Motor Overhaul:
- Three motors require bearing replacement, circlips, and appropriate lubricant
- Capstan motor type must be identified before lubrication
- Motor couplings, washers, and shims included in full kits
Pinch Roller Service:
- Replace with new roller including low-friction PTFE washers
- Metal shims for proper alignment
Brake and Solenoid Adjustment:
- If brakes don't release: Clean and adjust solenoid (section 2.2.3)
- Dirty contacts in push-button assembly: Clean per section 2.2.4
- Remote dummy plug must connect pins 1,2,3
Tape Counter:
- Original belt often deteriorated
- Replace with standard square profile belt
End of Tape Switch:
- Adjust per section 2.1.5
- Replace bulb Osram 3644 if defective
- Clean light port carefully (later optoelectronic models)
Complete Troubleshooting (from Service Manual)
| Symptom |
Cause |
Solution |
| Capstan motor does not run at either speed |
Speed switch in mid-position, defective switch, jamming motor, open winding, faulty condenser |
Switch to 3¾ or 7½ ips, replace wafer, clean bearings, replace motor, replace condenser |
| Noisy capstan |
Jamming bearing, damaged felt, loose flywheel, damaged bearing |
Clean/lubricate bearings, replace felt (SAE 20 oil), tighten nut, replace capstan assembly |
| Tape speed too low |
Jamming capstan, cold machine with thick grease |
Replace capstan assembly, run at 3¾ for a few minutes to warm up |
| Capstan runs at 3¾ but not at 7½ ips |
Speed switch contacts dirty |
Clean speed switch contacts |
| Pinch roller arm does not operate |
Dirty solenoid, dirty contacts, dummy plug removed |
Clean/adjust solenoid (2.2.3), clean contacts (2.2.4), connect remote pins 1,2,3 |
| Brakes do not release |
Dirty brake solenoid, dirty contacts, dummy plug removed |
Clean/adjust solenoid (2.2.3), clean contacts (2.2.4), connect remote pins |
| Push-button won't remain pressed |
Dirty contacts, dummy plug removed |
Clean contacts (2.2.4), connect remote pins |
| End of tape switch does not operate |
Incorrect threading, maladjusted switch, dirty solenoid, defective bulb, blocked light port |
Thread correctly, adjust (2.1.5), clean/adjust (2.2.3), replace Osram 3644, clean opening |
| Motor runs at power-on without command |
Failed FET or drive transistor (solid state models only) |
Check motor control transistors |
| Solenoid supply missing, 25Ω to ground |
Failed rectifier bridge, shorted relay coil |
Replace rectifier, check relay resistance |
| Smoke, burning smell, charred resistor |
Leaky paper capacitor, failed motor cap |
Replace all paper caps, check motor caps for charring |
| Hum, poor audio |
Bad electrolytic, ECL86 issue, weak tube |
Replace electrolytics, consider ECL86 mod, test tubes |
Real Restoration Cases:
Case 1 - Charred Resistor: "One of the three caps underneath these start caps has seen unhealthy things... it is charred, and the resistor on the other side... has been mightily charred." Solution: Replace all capacitors and check for underlying causes.
Case 2 - Missing Solenoid Supply: "'Pfft' noise and wisp of smoke... DC supply for solenoids and relays was absent. Resistance of feed from cap to relays was 25Ω." Solution: Check rectifier bridge and relay coils.
Case 3 - Hum Issues: "If you don't mind the built-in speaker you may remove the two ECL86 tubes, this will decrease HUM a lot." Caveat: Must change resistor value to maintain B+.
Calibration and Setup
Voltage Selection:
- Options: 110, 130, 150, 220, 240V
- For modern 125V mains: Set to 130V
- If set to 110V with modern mains, tubes run hotter than designed
Mechanical Adjustments:
- End of tape switch adjustment: Section 2.1.5 of service manual
- Solenoid adjustment: Section 2.2.3
- Contact cleaning: Section 2.2.4
- Bearing lubrication: Section 2.2.2
Electronic Calibration:
- Requires test tape (IEC curve)
- Oscilloscope for bias adjustment
- Signal generator
- AC millivoltmeter
- Full service manual available from Nagravox with restoration kits
⚠️ IMPORTANT: The G36 uses tube electronics - high voltages are present. Work with extreme caution and respect for safety.
Restoration Kits & Resources
Nagravox "Full Monty" Complete Kit:
Electronic Kit
HT/LT triple can caps, audio signal path caps, suppression caps, selenium rectifier replacement PCB with dropper resistors, trimmer pots
Motor Overhaul Kit
Bearings, circlips, appropriate lubricants for all 3 motors, washers, shims, motor couplings
Pinch Roller Kit
New pinch roller, PTFE washers, metal shims
Motor Capacitors
Specially made for Revox G36 - MUST specify your model/configuration
Accessories Kit
New RCA sockets, tape counter belt, VU/end-of-tape globes (Osram 3644), IEC mains lead conversion, knob felts, rubber mounts
Kit Price: Approximately $950-1045 AUD depending on destination. Includes comprehensive service sheets, before/after photos, and email/Skype/Facetime support.
Parts Sources:
| Supplier |
Specialty |
| Nagravox |
Complete G36 restoration kits, custom can capacitors, motor caps |
| Mouser / DigiKey |
General capacitors (Kemet), 1N4001 diodes, resistors |
| RS Components / Farnell |
UK/EU sources for motor capacitors |
| JRF Magnetics |
Head relapping, replacement |
| Tube retailers |
ECC81, ECC82, ECC83, ECL86 replacements |
Online Resources:
- Science Museum Group Collection: Original G36 service manual (MS/2179/023) and instruction manual (MS/2179/024) in archive
- Manualslib.com: G36 service manual with troubleshooting charts
- UK Vintage Radio Forum: Technical discussions on G36
- Audiokarma.org: Restoration threads, user experiences
- Nagravox.com: Service sheets, identification guides
Model Identification Guide
When ordering parts, provide:
- Serial number (determines tape end switch type)
- Hz stamped on reel motors (visible on rotors)
- Diameter of capstan shaft (3.0mm = 60Hz, 3.6mm = 50Hz)
- Poles stamped on capstan motor
- Whether operating 50Hz or 60Hz (or converting)
Production Run:
- Up to #36,500: Microswitch tape end sensor
- #36,501-58,000: Gold-plated wire contacts
- #58,001+: Optoelectronic sensing (light guide)
Specifications by Version:
| Parameter |
Value |
| Wow/Flutter |
<0.1% at 19 cm/s, <0.15% at 9.5 cm/s |
| Frequency Response |
40Hz-18kHz at 19 cm/s, 40Hz-12kHz at 9.5 cm/s |
| S/N Ratio (2-track) |
55dB at 19 cm/s |
| Power Consumption |
120 VA |
| Mass |
20-22 kg depending on version |
Common Mistakes to Avoid
- ❌ Powering up without replacing selenium rectifiers: Toxic fumes, catastrophic failure
- ❌ Wrong motor capacitor values: Motors run hot, won't start, or fail. VERIFY your configuration
- ❌ Removing ECL86 tubes without resistor mod: B+ rises to unsatisfactory levels
- ❌ Ignoring charred resistors: Indicates capacitor leakage - replace all paper caps
- ❌ Running at wrong voltage: 110V setting on 125V mains stresses tubes
- ❌ Forgetting remote dummy plug: Transport won't operate
- ❌ Not cleaning light port: End of tape switch fails
- ❌ Using silicon diodes without dropper resistors: Overvoltage damages circuits
Brittle Tape Playback Tip
If transferring old, cupping tapes that cause dropouts: "A drugstore cotton ball held lightly to the tape/head as a makeshift pressure pad will force the needed contact to fix the problem while the tape is being transferred." - Graham Newton, Audio Restoration.
This is not a G36 fault but a normal issue with aged tape stock.
