BY AARON DAHLEN
radios had a back cover to prevent
users from touching the chassis. Some
radios, such as the featured Philco PT-
44, have circuitry that isolated the line
voltage from the chassis. Unfortunately,
none of these safety measures will
protect you when servicing the radio.
The best safety measure is to be prepared for the worst. Obviously, unplug
the radio while you are working on it.
Use a voltmeter to check for voltage on
the capacitors as they can store a nasty
charge. Use an isolation transformer.
You should have a CPR qualified family
member or friend watching you. Instruct
them how to kill power to the radio in an
emergency. Tell them not to touch you
or the radio or they could become
victim number two. Finally, consider
safety modifications to the radio.
■ PHOTO 2. Beware of the live chassis
as indicated by the glow of the neon
lamp! Believe it or not, this is normal
operation for this type of radio. This
picture shows an unmodified Philco
“Hippo” radio chassis model 48-460.
Antique radios are inherently dangerous. The greatest danger comes from
the chassis being electrically hot. A GFI
power cord should be installed on the
radio to minimize this danger. You can
salvage a GFI power cord from a modern
hair dryer. Recall that a GFI is designed
to remove power if a ground fault is
detected, i.e., you have become part of
the circuit by simultaneously touching
the radio’s chassis and a ground.
Modern power cords are polarized
in that they only plug into an outlet one
way. (This can be a blessing and a
curse.) Polarized plugs work well for the
lethal power line directly connected to
chassis-type radios. Simply connect the
return (neutral) line to the chassis. For
radios such as the featured Philco PT- 44,
things are not as simple. As previously
mentioned, this radio has circuitry to
isolate the line from the chassis.
Unfortunately, the system is not 100%
effective. The power line is capacitively
coupled to the chassis. A 120 VAC signal will be felt on the chassis no matter
which way the power cord is connected.
You can verify this using a small
neon lamp as shown in Photo 2. If the
power cord is connected one way, the
lamp will always light. Connect the
power cord the other way and the lamp
will light when the radio is turned off.
You can rewire the power switch so
that it is in the opposite leg of the
power line. This is a simple operation
readily apparent when you have the
schematic in hand — not so apparent if
you are just looking at the chassis wiring.
This, plus the GFI power cord, should
protect you from your antique radio.
A fuse should be installed in the
radio on the hot side of the power line
at the point of entry. This will minimize
fire danger should the radio develop a
fault. Recall that your house’s circuit
breakers are designed to protect the
house’s wiring, not the electrical devices
that happen to be plugged into the wall.
Your radio would have to draw over 20
amps to trip the circuit breaker. It is
unlikely that this would happen. Instead,
the offending component(s) would heat
up, explode, or catch on fire.
To Modify or Not
commands a price over US$2,000.
Any modifications would spoil its
value. These radios belong in protective
display cases away from harm.
The Philco radio featured here is
considered a middle-of-the-road set. It
was only produced for one year, making
it rather scarce. It took me over a year
of on-and-off-again searching to find it.
The design is elegant and surprisingly
compact for a wooden radio. It is one of
the few radios that has a finished back
cover. This makes the radio ideal for
placing on a desk where all sides are visible. On the negative side, this radio
had moderate cosmetic damage. It suffered water damage, causing the laminations to part. The sides of the wood
cabinet had swelled causing misalignment. After restoration, these defects
are only visible upon close inspection.
It depends on your experience level
and on what type of radio you have.
Vacuum tube radios will never be made
again. Every time a set is modified or
restored, a piece of history is potentially
lost. Also, some radios are worth a great
deal of money. I’ve seen radios that sell
for thousands of dollars on on-line auctions. Your skill in restoring a radio will
have an impact on the ultimate historical
and monetary value of the radio.
If you are new to restoration, start
out with inexpensive radios. Start with
radios that are in desperate need of
restoration and have no historical value.
Watch the eBay auctions and you will
quickly learn which radios are sought
after. For example, I would think twice
before modifying a FADA 189 Catalin
Bullet radio. This type of radio is a
work of art. It is highly sought after and
Most consumer electronics are
designed to maximize manufacturer
profits. Vacuum tube radios are no
exception. The components —
especially capacitors — used in these
sets were chosen because they were
inexpensive and gave a relatively long
life. Unfortunately, they were never
designed to last 65 years. This is not to
say that all vacuum tube radios will
need servicing. I have a Hammarlund
HQ-150 receiver that works perfectly
and has never been serviced. This
radio is in a different league from the
Philco. It is a high-end, commercial
design that shares features with the
best military equipment of the era.
The capacitors used in antique
radios are almost exclusively paper foil
November 2006 37