Philips B5X74A radio (1957)

The B5X74A is one of the first so-called “Plano” models. These are radios with a low-profile cabinet with the speakers on the sides. It has a transformerless output amplifier and 800Ω spreakers. The transformerless output stage uses two output valves and results in low distortion and good bass performance. It is a further development of the amplifier used in the B7X63A but it uses the EL84 and EL86 valves instead. Philips had transformerless output amplifiers in most of their television sets after 1957 and in a lot of radio models. The valve line-up is:

• ECC85 as FM frequency changer,
• ECH81 as frequency changer for AM or first IF amplifier for FM,
• EF89 as first AM IF amplifier or second FM IF amplifier,
• EF85 as third FM IF amplifier,
• EABC80 as AM detector, FM ratio detector and AF pre-amplifier,
• EL84 as AF output amplifier,
• EL86 as upper AF output amplifier,
• EM80 tuning indicator,
• EZ80 rectifier.

I bought this radio in August 2023 out of nostalgia. It is almost identical to the B5X62A, one of which I had owned long ago but I had sold it. It was sold as slightly damaged, working unknown. It was a bit filthy, a candlestick had dripped wax on the side and back panel, but it didn't look too bad.

In March 2026 I started the restoration. From the production codes on the speakers and valves it was clear that this radio had been built somewhere halfway 1957. I hoped it would be an easy repair and started the regular checks and reformed the electrolytic capacitors without taking the chassis out of the cabinet. One odd thing: the 10A fuse in the heater circuit, was bridged by a piece of wire It looked like it was blown. I replaced it and checked the circuits. There were no signs of problems.

Then I connected it to my variable transsformer and turned up the voltage slowly. No sound. I connected an AF generator to the record player input and got sound. The voltages in the output stage and on the AF pre-amplifier were ok, relatively to the supply voltage that was a bit low. The voltages in the MF stages were confusing.

Now I knew I had to take out the chassis and do a proper repair. I had to remove one of the speakers to make room to let the the tuning dial pass. Inside the cabinet, a strip of wood had come loose that held the wiring to the speakers and two metal clamps that should keep the upper part of the frame holding the dial glass firmly to the front of the cabinet. After removing the chassis I hung it in my service brackets.

I carefully removed the dial glass and the light diffusion screen behind it. I connected a speaker. I tried MW and FM bands but no sound. After cleaning the switches with a mild contact cleaner I had reception on MW. But when I turned the tuning knob, the tuning capacitor hardly moved. This is a frequent problem of this type of radio. The mechanism that swaps the tuning knob to drive one of the two tuning capacitors starts to slip. The rubber roller round the shaft of the tuning knob was worn down and had become slippery. With a replacement for the rubber roller the mechanism was working again. I could tune in to Radio Caroline and get clear though weak reception on the built-in ferrite rod antenna.

Measurements showed that the EF89 was weak. Replacing it and the EZ80 rectifier improved reception a bit. After cleaning the FM section of the band switch, FM reception was working, too. The sound was good and mostly undistorted, but going through the band there was a weak secondary response on every station, meaning the detector and IF had to be realigned.

I decided to align the AM circuits first. This was a bit risky. This radio has a type of IF transformers that have a small brass alignment screw on top. Inside, a small ferrite core is attached to the screw by a plastic tube. These cores are notorious for falling off the screws, making any alignment impossible. But I had no trouble.

Then it was time to align the FM IF transformers. This is also risky, as they often have stuck cores. If you apply too much force while trying to turn the core, the coils may come loose and turn with the core, resulting in broken wires. To soften the wax, one can warm the cores or use some kind of solvent. Using eardrops, waiting half a day and carefully wiggling the cores to and fro, gradually increasing the movement, I was able to free them. I then connected my RF generator and aligned the FM IF transformers. I concluded by aligning the secondary of the ratio detector again. That was funny: turning the secondary core results in an odd cracking sound. As a result, FM reception was improved.

The mains switch had remained stuck in the “on” position during all this. After opening and lubricating, it worked again. I replaced the small felt patches that had come from between the bandwidth switch keys while cleaning them. These prevent the keys from scraping against each other and provide for an even spacing of the keys.

After this, I cleaned the tuning dial glass and diffusion screen and put them back in place.

Funny detail: at the edge of the dial glass the type number of the B5X62A, the predecessor model is printed. I cleaned the knobs and put them back. The chassis was complete again.

Then I thoroughly cleaned the cabinet and polished it. I filled a few deep scratches with shellack. I cleaned the speaker grills. I glued the wooden strip that had detached and left the glue to set for a night. I attached new foam strips around the opening where the dial glass sits. Then I reinserted the chassis and the speaker and reconnected the speakers. I screwed the two clamps that keep the upper rim of the dial glass to the cabinet and found out what the two 1.5cm large cubes of felt were for, that had initially been lying on the bottom of the cabinet: they were to be pinched between these two clamps and the metal supports of the dial glass.

Then I turned the radio on. With its original speakers and chassis back in the cabinet, the sound was really good.