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RADIO RESTORATIONS
BRINGING OLD RADIOS BACK TO LIFE
More on the Midget Arvin and
Sets You Don’t Want to Plug In!
Marc Ellis, N9EWJ
marcellis@monitoringtimes.com
In last month’s column, I mentioned how
my wish for a project radio small enough
to fit on my currently cluttered benchtop
seemed to have been almost providentially
granted. While attending the Antique Wireless
Asociation spring meet, which is always held
in conjunction with the AWA May board meeting,
I came across the perfect set: one of those
midget metal-cased Arvins. However, the very
diminutiveness that seemed to be such an asset
had the effect of stopping me in my tracks a little
earlier in this work session than I had anticipated.
But I’m getting ahead of my story.
I began this month’s work session with the
prospect of spending a few quiet hours recapping
the little Arvin. As regular readers know,
I start most radio restorations with replacement
of all paper and electrolytic capacitors. Turning
the set upside down, I took a good look at its
underside for the first time. What I saw caused
me to quickly abandon my plans for a wholesale
recapping.
The wiring is so tight in this little chassis
that it must have been installed in layers.
I thought I might do more harm than good as
I disturbed various connections to wire in the
new capacitors. It would be easy to create short
circuits as I moved parts around. So I decided to
use a servicing technique that would have been
normal for the era when the set was current: turn
it on, look for trouble, and correct any faults that
occur as they come up.
Rivets on the unusual cord restraint had to be
drilled out so it could be removed (see text).
❖ Needed: A Line Cord
But before I could power up this radio, I
would have to provide it with a line cord. The
original was clipped off where it entered the
chassis. Looking at the deteriorating remnants
of the cord left inside the chassis, I could see
why. Like most rubber zip cord of the time, this
one must have become a safety hazard with the
usual flaking insulation and exposed wire.
62 MONITORING TIMES August 2012
Making way for the new line cord turned
out to be a bit of a project. The remnants of the
old cord were held in a tight grip by a restraint
system I had never seen before. The cord was
sandwiched between a couple of small pieces
of insulating board that were riveted to each
other and the chassis apron. The rivets had to be
drilled out so that the restraint system could be
removed. Having done that, I replaced it with a
rubber grommet, ran the new cord through, and
prevented it from pulling out with a knot on the
inside of the chassis.
❖ Checking the Tubes
Once the new cord was hooked up, I removed
the radio’s four tubes and checked them
against the chassis layout shown in Rider’s
to make sure that the correct tube had been
installed in each socket. All the tubes checked
out fine on my Navy TV-7, though I wouldn’t
have been surprised to find one with an open
heater – which is one of the most common faults
in an a.c.-d.c. receiver.
With the tubes out of their sockets, I cleared
out most of the dust from the chassis and various
crevices using nothing more than a damp cloth.
Though there was plenty of dust, there was little
or no pitting – a sign that this radio had been
stored inside, not in a garage or shed where there
was no environmental control. Before each tube
was permanently seated in its socket, I sprayed
its pins with contact cleaner and ran it in and out
of the socket a few times.
❖ The Smoke Test
Now I was ready to try the radio – an
operation that seemed very strange to me with
the original capacitors still in place. I plugged
it in through a little autotransformer I have that
has four voltage steps – at about 40, 60, 80 and
120 volts. The autotransformer was powered,
in turn, through an isolation transformer. The
latter wasn’t technically necessary, since this
radio has a “floating ground” (see last month’s
column). That should protect the user from a
hot chassis situation, but its protection could be
compromised by a leaky bypass capacitor.
Before turning up the voltage, I set up a
multimeter to monitor the power supply’s d.c.
output by connecting it from the 35Z5 cathode
to the floating ground. A lack of d.c. voltage or
a sudden voltage falloff would be an indication
of a possible short and a signal to turn off the
radio immediately.
Turning the set on, I increased the autotransformer
voltage slowly, leaving it set at each
switch position for several minutes. There was
no smoke, but as I reached the 80-volt position
I began to notice a loud, raspy a.c. hum that was
unaffected by the position of the volume control.
This is the classic indication of one or more open
filter capacitors.
❖ The Capacitor Problem
The Arvin is equipped with a three-section
electrolytic capacitor. Two of these (40 uf and 20
uf at 150 volts) are filter capacitors and the third
(20 uf at 25 volt) is the cathode bypass for the
50L6 power amplifier. My next move would be
to change out this capacitor, but here’s where I
ran into trouble. None of the multi-section caps
in my stock could possibly fit in the tiny space
available. And even the most compact unit available
new was an inch too long.
The Arvin’s cramped chassis makes capacitor
replacement an adventure.
It looks as if the only course open to me
is to order three individual caps of the correct
sizes and somehow shoehorn them into the small
space available. Modern low-voltage electrolytics
tend to be quite small, so I’m hoping I
can make this scheme work out. Next month’s
column should tell the tale.
❖ Don’t Plug These Sets In!
This topic was inspired by a query that
recently came across the desk of our publisher,
Bob Grove. I knew some of the answer and, in
researching the rest, I came across some very
interesting material.
Here’s the issue: almost every serious radio
collector will eventually come across a routinelooking
radio, usually a table model in a wood
cabinet, that is designed to run on some value
of d.c. – generally 110 volts, 6 volts or 32 volts.
Quite often, the radio will be internally fried
because somebody in the past has mistaken it
for a routine a.c. model and plugged it into the
a.c. line.