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.
MAINS INPUT
This is very important and care and time spent examining this section of the radio is not wasted.
The most dangerous part of an mains-powered radio, is the mains circuitry. Check this first before plugging it in. A common and sensible practice amongst radio collectors, is to cut off the mains cord or plug, immediately that a new radio is acquired. This method removes the temptation "to plug it in and see if it works", which can quite often ruin a radio with a loud bang.
BEWARE
Before applying the mains voltage to the rado, it is also vital to check that there are no components that due to ageing or oveload have deteriorated and become internally short circuited.Such short-circuited components could possibly connect the active mains voltage to the metal chassis of the equipment. The metal chassis could then deliver a lethal electric shock when touched. Also, some electronic equipment (eg Televisions) were manufactured in the past with a "Live Chassis" The chassis istelf was connected to the live mains voltage!
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 240v is very likely to be lethal, although 12Ov is also a lethal voltage.
Many 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 especially important where you may later sell or give the item to someone else after working on it. If in doubt get advice from an electrician, a licensed electrical mechanic or electrical contractor or electronic technician.
Many types of early consumer electronic equipment was constructed at a time when electrical safety was not as carefully considered and many early radio sets etc have mains electricity wiring and metal mains voltage terminals fully exposed to touch once the metal chassis is removed from the wooden case or bakelite housing. For example, if, after you switch on the electrical power, you would try and lift a bare metal radio chassis sitting upright on the workbench, your fingers are likely to curl around under the edge of the metal chassis and could possibly contact the bare mains electrical wiring underneath where it attaches to say, the mains switch terminals, power transformer, fuse or indicator lamp. (Yes, fortunately the writer did survive this experience).
For this reason always support the chassis upside down with wooden blocks or similar supports before swithing on the power at the main switch. This way you can see which are the live mains points to avoid.
Also, the insulating materials in use in the old days were more of the organic (read biodegradable) type which can have perished or become brittle or just fallen off after many years of age and hot working conditions.
Some early and later television sets also had parts of the internal metal chassis inside the insulating plastic case connected directly to the mains voltage (Live Chassis!) Beware.
A complete safety check of the mains wiring and insulation and winding to winding insulation of the power transformer and everything connected to the mains wiring should be done before it is safe to connect an old radio or other equipment to the mains power.
Dont forget to stand back when powering up a tube radio or other equipment, even if you are sure you have checked everything. Its amazing how big an explosion an electrolytic capacitor can make when it has an internal short circuit and enough liquid electrolyte to boil up some pressure. Think of the biggest firecracker you have ever heard with the accompanying shrapnel!
Examine the mains cord, to see if the cable is safe, not perished, and no bare wires showing. Check for damage where it enters the plug and where it bends entering the chassis. Renew (or shorten) the cable if it is damaged. Use cable of the correct vintage and voltage rating and with insulation in good condition.. Use some rubber or cloth covered 3 wire cable from the junk box, or" figure eight" if the radio uses that type. An earth wire may not be required on these radios as they usually had a totally enclosed chassis and insulated knobs, but using a 3-wire cable and making the earth connection to the chassis is a good safely precaution if you are going to work on the circuitry. This way the chassis cannot become "live" if you drop a metal tool etc across the wiring.
For replacing the power cord, some hardware shops have "cotton covered" 3 wire mains cord for use on domestic clothes irons. This is suitable. Maroon coloured "cotton covered" mains cord may be available from vintage radio shops.
Examine the mains plug for cracks and bare wires, especially "whiskers", which may have escaped the wire holding screw.
Renew the plug, if it is cracked, burnt or dangerous, with a plug of the correct vintage.
Check the grommet or clamp on the chassis for wear or damage. Fix or renew it.
Check the ON/OFF switch with a multimeter to be sure that is is working and it has no short circuit to the chassis.
Check the power transformer connections.
Radios seldom have fuses, as they rely on the house fuse. Usually, this is all that is necessary.
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