Warning.
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.
Vintage Radios operate at lethal voltages. Take extreme care when working on live chassis.
If you aren't sure about what you are doing then don't touch!
Checking Filter Condensers
A handy tool consisting of an electrolytic condenser with a lead and test prod soldered to each terminal will enable filter condensers to be readily checked. To use the tool , simply turn on the set and apply positive and negative leads to the corresponding terminals of the condenser in question. The output of the set will improve if the filter capacitor is defective.
Checking Converter Operation
Connect a voltmeter of suitable range between the B plus connection of the oscillator coil and chassis, i.e., across the bypass condensor, and short circuit the oscillator section of the gang condenser to chassis. A reduced reading on the voltmeter indicates that the oscillator section is working.
The reason for the reduced reading is that bias across the oscillator grid leak is removed by shorting the gang. This in turn causes the triode section to draw more current, thus resulting in a greater voltage drop across the oscillator plate dropping resistor
Curing Oscillation
Frequently in circuits where persistent oscillation occurs and which cannot be traced to any circuit fault, it is possible that the various coil shields etc, are not as effective as they should be.
Where this fault is suspected, it is well worth the time and effort to remove these shields and tighten the rivets holding the spade lugs, which are used to hold the can to the chassis.