I recently got to work on a very nice large tabletop radio from 1936, the FADA 270T. This radio’s owner sent me the chassis and speaker only because of the radio’s size. It’s a 7-tube radio with a magic eye tuning indicator and a very attractive mirrored glass circular airplane dial.

This was quite the high end radio at the time with a very striking style and 7 tubes, 6A8 6K7 6G5 6H6 6F5 6F6 5W4.

Not only does this radio have a beautiful high visibility dial and 5 knobs, it features dual speed tuning, and variable selectivity with an indicator behind the dial face controlled through a mechanical linkage to move the band card behind the dial. The two-speed tuning kicks in over a very small frequency range, and tuning beyond the range of the fine adjustment engages the fast tuning speed. Simply tune slightly past the intended station, then turn back the other direction to engage the fine tuning and use the tuning eye to precisely dial in reception of your favorite programs.

This radio had seen service a few times in the past, and apparently was kept going all the way into the ’60s.

New tubes and new capacitors in 1966; adjusted for inflation, that’d be a series of $150 service calls today. Components age and fail, and in the ’60s the wax and paper capacitors were getting to be 30 years old – they often failed within years when new, so the fact any original parts occasionally survive is nearly a miracle, but somehow a few do last – until they don’t.

I’d expect this shop hasn’t been in business for a while, but you never know.

This radio had a phono input from the factory, controlled by turning the volume control all the way to the left, switching the audio circuit and delegating volume level control to the device supplying the signal.

Underneath, the shop dida good job installing repair parts, for the most part. FADA has such a well organized chassis, it’s easy to follow and keep it that way.

All of the tubes test good, including the eye tube which lights up brightly.

During one of the past failures, the output transformer must have died as it’s been replaced by a vintage universal output transformer. The transformer supports both push-pull and single ended; in this case the other side has been left disconnected for single-ended operation.

Time to start component replacement. First up were the two line-to-ground capacitors providing noise filtering and an RF path through the wiring, replaced with X1Y2-rated safety capacitors.

Replacing components on the terminal boards was very neat and easy.

Several tubes had RC combinations for their cathodes; I replaced these as a unit.

Overwhelmingly, the resistors measured in tolerance, but a few had drifted. Surprisingly these had drifted low – most dogbone resistors drift high – but in some cases, that could even be worse.

As they came up, I replaced the electrolytic capacitors. From the factory, they were 8 – 8 – 6 uF; I’ve replaced those with 10 – 22 – 10 to up the filtering a bit while staying within circuit tolerances. Since the new components were so much smaller than the old ones they could be located nearly anywhere – this let me move them to areas I could mount them more securely and more easily, while still preserving the electrical layout on the schematic.

At some point, the second filter capacitor (the second 8 in the 8 – 8 – 6) was replaced with a Sprague 80 uF 450V electrolytic capacitor. That’s much too high even after the field coil; if this were the first capacitor it would likely cause serious damage to the rectifier tube.

In this case, since these had huge tolerances, this one tested 116.3 uF. ESR and Vloss indicate it’s technically still good, though.

More R/C combinations:

Continuing:

And finally the first electrolytic was moved directly to being mounted on the rectifier tube socket itself.

On the left wall there’s a dual section electrolytic cardboard capacitor, consisting of two 10 uF 25V electrolytic which are used as the bypass capacitors on the 6F5 driver and 6F6 audio output tube.

I’ve grabbed Nichicon 10 uF 50V capacitors, which are tiny compared with the original – they can be relocated right to where they’re needed.

The 10 uF 25V dual section had burst and come unsealed:

The replacements were relocated directly onto the tube sockets:

Overall, it’s much cleaner under there!

This radio got a new power cord with an integrated safety fuse, but has a rounded metal strain relief opening so no rubber necessary.

Luckily, this one came with a phono input already! I ran a female RCA cable out one of the screw holes from the box electrolytic capacitor, and connected it to the existing circuitry inside.

On to the outside – the eye tube socket was wrapped up with 1930s era electrical tape, showing the tiniest corner of the dogbone resistor.

The speaker was pretty hacked on, too, with exposed solder joints. Every joint in this connection has several hundred volts exposed on it, so this was extremely dangerous. I snipped those joints out, re-tied them using lineman’s splices and re-soldered, then covered with heat shrink tubing.

Time for a power-up!

One dial lamp out of three was out, so it was replaced. The first power-up is without the rectifier to check for heater or transformer internal shorts. Then, time for the first power-up with the rectifier. This was a bit exciting – as soon as B+ came up there was an arc under the 6K7 and the radio didn’t receive anything. There were no burned components visible, or further arcing, and just a tiny burnt spot near the ground rivet it arced to. I saw some dust wedged around the tube pins and assume that was the cause of the arcing which must have vaporized the dust which caused it. The tube socket pins on the 6F6 weren’t making good contact, either, which kept the tube from operating.

The metal 6F6 tube gets absurdly hot – we’re talking, leave pieces of your skin behind if you accidentally give it a good brush. Hot enough they routinely burn off their high temperature paint. There was some lingering distortion, though – I ended up replacing the 6F6, which was developing pretty serious distortion after warming up, with a NOS metal 6F6, and replacing the 6H6 detector tube to clear up some remaining distortion at the low end.

With those repairs made, it fired right up and sounds fantastic!

The eye tube is very striking, too, and glows very brightly. A properly working eye tube is incredibly attractive! It also helped with the alignment, as the radio came into correct alignment on a station or RF signal generator, the eye would close. This helped peaking up the RF tuning and the IF transformer resonance. The alignment was off by quite a bit initially – my favorite reference station, KIXI 880 AM, was coming in about 960 AM. Using my signal generator, I followed the alignment procedure from the schematic and the reception improved greatly; 880 coming in dead at 880.

I really enjoyed working on this radio – it had an interesting repair history, great design and interesting circuitry, and needed a little detective work to get going again at maximum performance. It’s going to be a great conversation piece and functional music player for a long time.

More Rain City Audio Projects

Vintage Radio Repair