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