POWERING UP A RADIO
There are different methods for powering up a radio.
If the radio had been dormant for many years, it may not have been
working when it was put in storage, so it may have a 50 year old fault,
as opposed to a fault caused by age.
However if the radio was working and has just stopped, then normal
fault finding can be attempted.
PROTECTION DEVICE
A simple protection device can be made. It is simply a 100 watt
incandescent light globe and a switch. It can be placed in series with the
mains cord during testing. This will act like a fuse. If there is a short
circuit, the bulb will shine at full brilliance. If the radio is working
normally, the bulb will glow just a little.
FOR THE FIRST TIME (SLOWLY).
A variable transformer called a VARIAC is a useful device for slowly
bringing a radio to life. You can slowly turn the knob and apply the
mains voltage, from zero to 240 volts over several hours. The range from
180 to 240 is crucial, as the valve rectifier suddenly starts to work and
the HT is applied. Be careful and take your time. In later model radios,
if the rectifier uses semiconductor diodes, then this doesn't apply, as the
HT voltage is always a proportion of the applied AC.
FOR THE FIRST TIME (STEP BY STEP)
Another method, is to test the radio section by section, and turn
the radio OFF between each test.
Start by drawing a diagram of what valves go where. Then CAREFULLY
remove the valves and place them in a box with tissue paper. Grip them
by the base, not by the glass, as this may break the bond between the
base and glass. Pull them straight up, do not wiggle. If the valves
have no makings, attach a paper label to their base, with the type or location.
Don't assume the valves are correct, or that they are working, or in the
proper socket, as someone may have attempted to fix the radio before you.
Check the mains wiring, cord and plug.
Put a meter across the primary of the transformer, set to 250 volts
A.C. or greater.
Turn the radio OFF.
Turn the power socket switch OFF.
Plug in the mains plug.
Turn the power socket switch ON.
Check for smoke. Listen for sparking.
Turn the radio ON
Check for smoke. Listen for sparking.
Check there is 240 volts AC reading on the meter.
Turn the radio OFF and the power socket switch OFF.
Move the meter, to read the heater voltage (a convenient place
is across the audio output valve socket).
Set the meter to 10 volts AC or greater for 6 volt valves. Set it appropriately
for different valves.
Turn the power socket switch ON and the radio ON .
A reading of the correct heater voltage, means that the power transformer
is working, and that there are no short circuits on the heater wiring.
Repeat this procedure for the high tension winding.
This is usually 250 AC (or 385 AC) and can be checked at the rectifier
valve socket.
If this is all correct, then plug in the audio output valve ONLY.
Its heater should glow correctly.
If this is all correct, then plug in all the other valves, but
not the rectifier.
They should light up correctly with a dull red glow.