(Photo 15). The next power-up after
reconnecting the broken wire started
pulling in AM stations on the first try
(just like it should) with a very short
test lead antenna.
If you're still having trouble
getting the radio to make sounds
after the component replacement,
you'll need to do some more in-depth
diagnostics. Double-check that
everything is plugged in correctly. If
your radio has top caps on the tubes,
make sure they're connected. You
can carefully tap each of the top caps
with the metal end of a screwdriver
and listen for a click in the speakers.
If you don't hear any clicks, it means
there's a problem keeping the signal
from passing through the radio
Clicks but still no reception might
mean there's a problem with the
radio's oscillator or front end keeping
the radio signal from being received
correctly. Ask for help on a forum if it
doesn't seem to be going anywhere.
The De Wald is now pulling in
stations, but not quite at the right
spot on the dial. It's time to fix that!
Aligning the Radio
Alignment is the process of
adjusting the radio's tuned circuits so
stations come in loud, clear, and
ideally at or near the correct
numbers on the dial. While these
radios would certainly have peaked
up perfectly when they were brand
new, age-related changes in the coils
and adjustments can make this part a
little more difficult. Sometimes the
best you can do is "close" but not
"perfect." Don't worry too much
If your radio has a set of
alignment instructions, go ahead and
follow those. There are usually two
parts to the alignment: IF alignment,
where you adjust the transformers to
get signal through the radio as
efficiently as possible; and RF
alignment, where you adjust the dial
tracking and positioning. You can
generally adjust both with simple
tools like your multimeter and a small
screwdriver — or even just your ears!
In the Rider's Perpetual
Troubleshooter manual for 1937 — a
great resource for radio repairs —
De Wald provided alignment
"IF Alignment: Intermediate
frequency peaked at 456 KC.
Connect test oscillator to grid of 6A7
and chassis. Short circuit stator of
front section of variable condenser
during this operation. Then, peak IF
trimmers for maximum signal."
That's a little bit complicated with
the old terminology, but not too bad.
To follow those instructions to the
letter, you'd set the signal generator
to put out a modulated 456 kHz
output through a series capacitor to
the grid of the 6A7 tube, and
connect a jumper across the front
tuning capacitor section to short out
the incoming signal and ensure
you're only getting the test
generator's input (Photo 16).
Then — with your multimeter
hooked up across the speaker's voice
coil — adjust the trimmers on the top
of the IF transformers for the highest
observed voltage. Start out with the
last IF transformer closest to the
radio's detector, and work your way
back to the front towards the 6A7, in
If you don't have a modulated
signal generator, you can still do this
step by ear. Tune into a loud station,
set the volume about mid-way, and
listen to the program as you adjust
the trimmer for maximum volume
and the highest reading on your
multimeter. It's that easy!
You'll probably be able to get a
tiny bit better results using the full
test set, but realistically, you're
unlikely to notice a large difference if
you just align the IF chain "by ear"
versus with a signal generator.
Next up is the RF alignment.
De Wald says:
"Remove short from stator of
variable condenser. Turn wave band
switch to Broadcast. Connect test
oscillator to antenna and chassis. Set
test oscillator and radio dial to 1500
KC and peak var. Cond. Trimmers for
maximum signal. Set test oscillator
54 June 2015
Photo 16. My signal generator — the LogiMetrics 921A — hooked
up to an HP 3585A spectrum analyzer for monitoring.
Photo 15. Broken field coil lead.