Old Radios Troubleshooting Quick Guide

How to detect old radio malfunction cause? The most common fault in antique receivers and their characteristic symptoms:

Absence of Signals

• Burnt out rectifier valve
• Broken down filter capacitors
• Open-circuit field winding or filter choke
• Short in H.T. by-pass capacitors
• Open circuit cathode resistors
• H.T. supply line open circuit
• Open circuit R.F. or I.F Coil
• Shield can shorting to grid cap
• Disconnected wiring
• Faulty valve socket or speaker connection
• Low B+ Voltage

Poor Volume

• Weak valves
• Low H.T. or filament voltage
• Poor alignment
• Open circuit R.F. or I.F. coils
• Faulty volume control
• Incorrect valve types
• Leaky high voltage caps

Distortions

• Open circuit bias or grid resistors
• Audio feedback
• Low emission valves
• Incorrect voltages
• Leaky coupling capacitors
• Gassy output valve

Crackles & Whistles

• Faulty resistors
• Faulty capacitors
• Loose contacts at sockets
• Dry joints
• Faulty output transformer
• Faulty power transformer
• Ineffective valve shield( Whistles in particular)
• Faulty valve
• Poor wiring layout
• Poor alignment

Hum

• Poor filtering
• Short between cathode & heater
• Poor shielding on audio leads
• Bad rectifier
• Faulty electrolytic capacitor

Severe Hum

• Shorting electrolytic capacitor
• Internal fault in rectifier
• Shorted field coil or H.T. choke

No Shortwave reception

• Dirty wave change switch
• Resistors high in R.F. stages
• Weak frequency changer valve
• Low H.T. voltage

Low High tension

• Weak rectifier valve
• Faulty power transformer
• Incorrect speaker
• Faulty valve

Rectifier glowing red

• Direct short on H.T. Line. (e.g. Electro filters)

Output valve red

• Open circuit anode on output valve
• Open circuit output transformer
• Speaker unplugged