Ever Want to Know How to Repair an Antique Radio? 

The process is similar with all Retro, Vintage or Antique Tube Radios so follow along. Some specialized equipment is used and the following scenario details a typical job that presents itself. 

 You can receive a refresher HERE on How an AM Radio Works. If youd like to formally educate yourself on How to Repair A Tube Radio, you can take the online Antique Radio Repair Academy ARRA course.

Today, we are going to answer the question, "How to Repair An Antique Radio", Specifially, a Northern Electric 5508, or “Bullet” as collectors call it. 

This radio came into the shop not functioning and needing a cabinet restoration. The cabinet is very rough with two layers of, what I’m sure is heavily lead laden, paint that has been applied over the original red hammered finish. We will get to that later but first let’s get the set electrically working strong.

While it can be tempting to dive right in and attempt diagnostics, it’s best to have a systematic approach that is applied to each repair job. Often the issue presents itself during the work flow process.

The first step in how to repair a tube radio is to removed the chassis from the cabinet, store the screws and knobs securely and then give the chassis a good cleaning. This one, as you can see, has many years of dust bunnies throughout. Using compressed air, an auto detailers fine brush, towelettes and Q tips, the cleaning begins.

Once the cleaning is finished, the volume potentiometer shaft gets a light lubrication and the inside gets deoxidized with a special agent such as De-Oxit. The tuning condenser receives a light lubrication and test for shorting of plates, malignment or degradation of mounting grommets. The dial string and lamps, if applicable, are examined at this time.

Next, in how to repair a tube radio, all the tube sockets receive a deoxidization and the tubes are tested. In this set, the 12BE6 failed on the old trusty Knight tester. We have many in stock so replaced it with a new one. If you are looking for a tube source, Pacific TV is a good one. All others tested well.

The next step is to reference the schematic from our database and replace all the wax/paper capacitors and the electrolytic filter condensers. In addition, here are a few sites to obtain schematics if you need.

• Radiomuseum.org
• Nostalgiaair.org
• Pacific TV

The capacitors often degrade over time and fail. They are relatively inexpensive and, in keeping with preventive maintenance, all get upgraded. 

Then all resistors are checked for drift or open status. Typically anything approaching 20% disparity is replaced. All of these were under 10% variance.

Solder connections and wire condition is now carefully examined. Nothing incongruous was obvious at this point. A new power cord, and power plug is installed with an X rated safety capacitor replacing the line filter. X and Y safety capacitor information can be found HERE

At this point it is time to light the set up and see what happens. As always, when considering how to repair a tube radio, a DIM bulb Tester (DBT) is used inline with the power cord. Here's more information on the Dim Bulb Tester. Most importantly though, because this is a hot chasis set, an isolation transformer is used. See critical information on hot chassis sets HERE. 

After slowly bringing up the power using a variac, you can see a light glow on the DBT. This indicates there's no short or significant current draw. The set then emits a slight low hiss with no stations. Ok, well, time to dig a bit deeper.

Using a Signal Generator, a 455khz signal was injected into the sets front end. Voila, the tone made by the generator booms through the speaker. The audio amplifier section and IF transformers appear to be working. We suspect now that the local oscillator has quit running so focus on this area.

Using a signal tracer, one very weak station is heard on the grid or input of the 12BA6 tube but nothing is heard on the plate or output. This is a strong local station but none others are heard. More info on Signal tracing HERE when considering how to repair a tube radio. 

It’s at this point the oscillator coil windings are checked with a dvm. Aha! One of the coils is open. After close examination, one of the very fine hair like wires had broken loose from its lug. They are so tiny it was easily missed visually. After bridging the wire, the set came back to life!

Ok, now that it’s singing again, time to finish the servicing. Using the RF signal generator the radio is aligned or “Tuned” as per the published procedure with the schematics.

This radio is to receive an aux input for a Bluetooth module so Retro radio Shop Aux Input Board is wired into the set. The discreet Aux Input Board board contains, audio summing resistors, a micro switch, 3.5 mm plug and, most importantly, an isolation transformer. 

After reassembly, the radio is played for a number of hours to ensure stability. We listened to this one while stripping and prepping the cabinet for new custom finish as per request. Not the scheme we would go with but the customer is always right! 

Hopefully this has helped you better understand how to repair a tube radio. Stay tuned for future instalments!