Radio Servicing Information
For use by legally qualified and licensed repairers only
Countries have laws regulating who is legally allowed to repair or work on electrical equipment that will be plugged into the mains electricity supply. This is to protect the public from the risk of electric shock. If you are not lawfully allowed to repair electrical equipment yourself, you must find an electrician, a licensed electrical mechanic or electrical contractor or electronic technician to do any work on the equipment.
Different countries use electricity supply at different voltages. The United States uses 110-120 volts AC. The United Kingdom and Australia (amongst many other countries) uses 240 volts AC. Any electric shock at Voltage 110v or above is likely to be lethal.
Many types of early consumer electronic equipment was constructed at a time when electrical safety was not as carefully considered as is required under manufacturing laws today, and many early radio sets etc have mains electricity wiring and metal mains voltage terminals fully exposed to be touched once the metal chassis is removed from the wooden case or bakelite housing.
This is why any electrical work to restore or repair an old radio must be done by a licensed qualified technician.
YOU MUST NOT ATTEMPT TO REPAIR THE RADIO YOURSELF UNLESS YOU ARE LEGALLY ALLOWED TO DO SO.
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
Distortion
* Open circuit bias or grid resistors
* Audio feedback
* Low emission valves
* Incorrect voltages
* Leaky coupling capacitors
* Gassy output valve
Crackles And 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