become energized at your mains
voltage and any contact with an
earth ground — like a concrete floor,
a cold water pipe, or a piece of
grounded test equipment — could
cause a short through your body or
your gear. Bad news! Don't chance it!
Use an isolation transformer and stay
safe (Photo 13).
After making sure you're safe, flip
the switch and hold your breath! This
is the part where you'll see smoke if
there's a problem (Photo 14). On
most radios, the switch is on the
volume control, so just click it on but
don't turn the volume up yet.
Otherwise, turn the volume all the
way down and flip the power switch
Do the glass tubes start to glow
a little inside as their heaters fire up?
On a transformerless "series string"
radio, if any tube has an open
filament or heater, they'll all fail to
light and the radio won't get any
power at all. So, if you have no
power, double-check that the tube
filaments aren't open.
Listen for sparking and arcing. If
you hear any, power the radio off
right away and look underneath to
see where it's shorting out and
correct that problem.
Do you see or smell any smoke?
Likewise, power-off immediately and
look to see what went wrong. If it's
not obvious, you might need more
in-depth diagnostics with help from a
www.antiqueradios.org) or the
Audio Repair community on Reddit
audiorepair) if this is your first
If all you get is a loud 60 or 120
Hz hum that doesn't vary with the
volume control, stop. You have an
issue with the power supply and
need to double-check your filter
capacitors. Most of the time the
negative terminal of both capacitors
will connect to circuit common, but
occasionally you'll find a negative-filtered power supply where both
positives connect together, but the
negative ends connect to different
One common pitfall is failing to
notice that, say, one of two cans on
top of the radio chassis is actually
insulated and connects to a different
negative than the other. Check your
connections against the schematic
and ask for help if you're still having
trouble. Don't run the radio in this
condition as you'll likely cause a filter
capacitor to explode like a firecracker
or damage your transformer.
I flipped the switch and listened,
but got absolutely nothing from the
speaker. After poking around at
various connections and test points, I
found the problem pretty quickly: A
lead going to the field coil on the
back of the speaker had broken! That
would pretty much take the power
supply out of the circuit.
Fortunately, this was an easy fix,
and I was back up and running
June 2015 53
Photo 14. First power-up
with the lights on.
Photo 13. Isolation transformer for safety.
Photo 12. Component replacement complete. Looks good!