Nuts and Volts - June 2015

(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 properly.

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 about it.

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 instructions:

"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 this case.

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