Kenwood TL-922A Service Manual

The Kenwood TL-922A is a high-performance amateur radio linear amplifier designed for HF band operation. This service manual provides comprehensive technical information including circuit diagrams, alignment procedures, troubleshooting guides, and maintenance instructions for qualified service technicians. The amplifier features vacuum tube operation, automatic band switching, and robust protection circuits.

1. Technical Specifications 2. Block Diagram Overview 3. Circuit Description 4. Alignment Procedures 5. Tube Replacement 6. Voltage Measurements 7. Troubleshooting Guide 8. Parts List 9. Safety Precautions 10. Schematics

Technical Specifications

Detailed technical specifications for the Kenwood TL-922A linear amplifier.

Parameter	Specification
Frequency Range	1.8-30 MHz (all amateur bands)
Output Power	1000W PEP SSB, 1000W CW
Input Power	100W maximum drive
Tubes	2 x 572B or 2 x 3-500Z
Power Supply	Built-in high voltage supply
Band Switching	Automatic with transceiver
Cooling	Forced air cooling system
Input Impedance	50 ohms unbalanced
Output Impedance	50 ohms unbalanced
Power Requirements	120/240V AC, 50/60Hz

Block Diagram Overview

System block diagram showing major functional sections.

RF Input Circuit: Pi-network input matching
Driver Stage: Pre-amplification section
Power Amplifier: Final amplification with 572B/3-500Z tubes
Output Network: Pi-L output matching network
Power Supply: High voltage and bias supplies
Control Circuit: Protection and sequencing logic
Cooling System: Blower and thermal management

WARNING! High voltages present - lethal shock hazard. Only qualified technicians should perform service.

Circuit Description

Detailed circuit analysis of major sections.

RF Input Circuit: Provides impedance matching and protection
Driver Amplifier: Class AB1 operation for linear amplification
Final Amplifier: Class AB2 push-pull configuration
Output Network: Broadband pi-L network for harmonic suppression
Power Supply: Transformer, rectifiers, and filtering
Control Logic: Sequencing, timing, and protection circuits

CAUTION! Always discharge high voltage capacitors before servicing.

Alignment Procedures

Neutralization: Adjust for minimum feedthrough
Input Matching: Tune for maximum power transfer
Output Network: Adjust for proper load matching
Bias Adjustment: Set proper idle current
Protection Circuits: Verify proper operation
Band Switching: Confirm proper relay operation
Meter Calibration: Adjust for accurate readings

Tube Replacement

Proper procedures for tube replacement and testing.

Steps: POWER, OPEN/CLOSE, AUTO/DPMS, MUTE.

Procedure: Allow amplifier to cool completely. Disconnect power. Remove covers. Discharge high voltage. Remove old tubes. Install new matched pair. Reassemble. Perform bias adjustment and neutralization.

Voltage Measurements

Critical voltage test points and expected values.

Plate Voltage: 2400V DC nominal
Screen Voltage: 400V DC regulated
Bias Voltage: -60V DC adjustable
Filament Voltage: 5.0V AC
+12V Supply: For control circuits
+5V Supply: For logic circuits

Tip: Use high voltage probes rated for 5kV or higher.

Troubleshooting Guide

Common problems and solutions for the TL-922A.

Symptom	Possible Cause	Corrective Action
No output power	Tube failure/bias	Check tubes; verify bias voltage; test driver stage.
High SWR	Output network	Check output network components; verify antenna system.
Overcurrent trip	Faulty tubes/shorts	Test tubes for shorts; check power supply components.
No band switching	Control cable/relays	Verify control cable; test band relay operation.
Poor linearity	Bias adjustment	Readjust bias current; check neutralization.

Parts List

Critical replacement parts and components.

Tubes: 572B or 3-500Z (matched pair required)
High Voltage Capacitors: 0.1uF 3kV
Power Transformer: TL-922A specific
Band Relays: RF switching relays
Blower Motor: Cooling system
Meter Movement: Front panel meters
Control ICs: Logic and timing circuits

WARNING! Use only genuine Kenwood replacement parts.

Safety Precautions

Essential safety procedures for service technicians.

CAUTION! Lethal voltages present. Always use insulated tools. Discharge all capacitors. Work with one hand when possible. Use safety glasses.

Schematics

Complete schematic diagrams included in PDF version.

Main Amplifier Circuit
Power Supply Schematic
Control Logic Diagram
Front Panel Layout
PCB Layout Diagrams
Wiring Harness Diagram

For complete schematics, download the PDF version of this manual.