Becker Europa Valve Car Radio Faults and Repair

Do you have a vintage Becker Europa High Fidelity vacuum tube car radio that you want to fix? If so, I’ll run through several faults and fixes that could restore your Becker for that classic sound.

Warning: Valve car radios like this Becker generate dangerously high voltages inside even though they run from the 12v car battery supply. Never operate your car radio with the covers removed.

This Becker Europa High Fidelity car radio, designed in the 1950s, uses valve or vacuum tube technology for both radio and audio frequencies. So you may wonder why anyone would want to restore and use it in today’s DAB digital age. The answer is its unique sound quality that adds authenticity to a vintage Mercedes and Porsche car to which these were first installed.

Working Becker valve car radios are a rarity and I took on this as a challenge for a friend who’s lucky enough to own a Mercedes of the era. It was indeed a challenge but is now installed and working with an incredible authentic sound.

Becker’s Europa range included several different models. This High Fidelity moniker was at the time meant to reflect the fact that it received FM radio rather than lower quality AM. Yes, FM preset tuning was available way back in the 1950s! It was also known as the Europa MU or MU Export.

With an EL84 class A audio output stage, the Becker does indeed sound hifi when connected to a good quality 4 ohm speaker. None of the raspy crossover distortion often heard from transistorised radios. This was the main reason for my restoration request.

The final tally of workshop time taken to revive the Becker was something over 25 hours. I will admit I’m not an expert on valve technology and so I went down a few rabbit holes as I’ll explain. In the end the faults I discovered were a combination of age related ‘component failure’. I hope by reading this you can target the issues and fix your Becker much faster.

While I can’t guarantee your Europa will be suffering the same maladies, I have only seen one of these, it’s worth checking out the faults I found and replacing the suspects components given the radio’s age.

If you’re in a hurry I’ve listed all the faults and fixes here.

The faults

This Europa arrived complete with separate power unit completely dead. All I knew was that when it was last connected it smoked. An ominous sign.

First, the relay

Powering up the Becker, using a bench 12v supply, failed to consume any current or generate any smoke. The circuit diagram, see useful links below for details, showed a relay inside the power unit that I suspected. The main of/off switch on the radio’s volume control operates the relay. A static measurement with a multimeter showed the relay’s contact resistance between 24 and 200 ohms – clearly far too high.

Cleaning the relay’s black oxidised contacts with silver polish and contact cleaner produced signs of life. With the bench supply’s current limit set to 3A, the supply voltage dipped to less than 7v indicating the relay was now providing power to the radio. But it was consuming a high current.

The rabbit hole

In order to generate the 240v DC necessary to power the Europa’s valves Becker employed a step up transformer inside the power unit. This provides the high voltage to the audio output stage and via the 10 way plug lead to the radio itself. But 12v DC from the car’s battery can’t drive the transformer directly as it needs an alternating current. So Becker used an electromechanical vibrating device, much like an old fashioned bell, to generate an AC frequency.

I could not hear the device hum when I applied the 12v from the bench supply so I assumed the electromechanical device had failed much like the relay. Maybe this is why it consumes the high current?

So I went off to seek a replacement. Several fruitless hours later I realised electromechanical vibrating devices had long been consigned to history and now only used for sex toys!

I found another solution by replacing the old low frequency transformer with a modern high frequency step up voltage generator. Several circuit board modules are available from Amazon and eBay with a 12v DC input and 220 – 400v DC or AC output. I selected a module that could fit in place of the redundant bridge rectifier in the power unit and waited for it to arrive.

A few days later I hooked up the set up module, set it to 240v DC and connected it to the power unit’s reservoir capacitor via a limiting resistor to see if it could power the radio. I’d unplugged the suspect electromechanical vibrator to isolate the low frequency transformer and disconnected the bridge rectifier.

Still I found the bench supply dropping as it hit the 3A current limiter. My instinct was to switch off after a few seconds but then I realised something else. Valve technology needs filament heaters to generate the electrons necessary to function and these heaters for all five valves were all powered from the 12v supply. A quick DC resistance test showed the radio and power unit measured just 2.5 ohms when cold. However when the filaments warm up their resistance increases so the current consumption decreases.

With trepidation I powered up the Becker again and this time left it on for longer as I monitored current consumption and both low and high supply voltages. After ten or so seconds the current dropped to 2A and turning the volume control up a faint static emerged from the speaker.

Success? Not quite. After a minute or two the high voltage dropped to 220v and then plunged to 150v when the static went quiet. Something not quite right.

The Reservoir capacitor

I noticed the large electrolytic capacitor in the power unit was hot and a white electrolyte emerging from its vent suggested where the next fault lay.

Both power unit and radio contained 50uF 385v DC metal encapsulated electrolytic capacitors. I had some black plastic clad 47uF 450v electrolytics I’d ordered for my Quad II amplifier and used these to replace the aluminium canned caps in the Becker. The one in the radio had not become warm or vented but clearly they were well past their use by date and needed replacing.

As the new cans were smaller diameter, I fitted 25mm diameter capacitor clips to fix in place. The original capacitors had three tabs that secured the can to the chassis and provide the negative terminal with a single central tag for the positive terminal. My replacements had two terminals and so I offset the capacitor clips so the positive terminal lined up centrally and the negative terminal aligned with one of the three chassis holes.

I wired the negative terminals back to the nearest chassis solder tag rather than attempt to solder directly to the steel chassis. You need a powerful soldering iron to solder the chassis directly as it acts as a giant heatsink!

The smaller electrolytic capacitors

I decided to replaced all the smaller electrolytic capacitors, shown with orange and light blue cases, as routine given the age of the radio. There were nine in total ranging from 1 to 100uF at various voltages. I ordered new 400v axial capacitors as I had none in stock.

While replacing the radio’s capacitors I knocked an inductor which then dangled via its thin wires. I had to glue it back in place using epoxy then clean the chassis where the previous fixing had disintegrated. Notice Becker radios, like many from this era, have no central printed circuit board. The discrete components are wired point to point with the odd tag strip to bridge between.

With all the electrolytic capacitors replaced I powered up the Europa and had time to tune into FM stations without the HT voltage dropping. I’d hooked up a Q-Acoustics 2010i 6 ohm speaker for testing and local talk radio sounded reasonable. Music was not so good, it lacked bass and seemed disappointingly distorted. At least it was working as a radio.

Further down the rabbit hole

Monitoring the Europa’s current consumption from cold start, via warm up, to running I noticed an odd pattern. It started around 2A then fell a little, then increased to over 4A where my bench supply limited to less than 10v. Maybe this was causing the distortion? The documentation available online gave no idea what the Europa’s normal current consumption should be.

So I tried using a PowerOak inverter that kicks out over 10A at 12v instead of the bench supply. For safety, I wired in a 5A fuse. The PowerOak lived up to its name. Current consumption peaked to around 5A and then after a few minutes the relay cut out.

The relay’s reprise

I measured a small voltage drop across the relay’s contacts and guessed the oxidisation was still a problem and decided to replace the old relay. I used a Siemens 8A rated 12v relay mounted on a small circuit board. There’s limited space available for a larger relay.

With new relay and the stable PowerOak supply I switch on again to monitor the radio’s current consumption from a cold start and listen. Each time the current consumption would slowly increase with audible distortion, most obvious on music programmes.

So I checked the EL84’s voltages and found the voltage across R5 was much too high. It measured 16.6v instead of 6v and explained the high current drain.

I discovered the excessive power consumption was due to a leaky audio coupling capacitor as shown below – it was supposed to measure 0.01µF. It looks like its paper insulator had aged and become conductive. As the EL84’s grid circuit is high impedance and voltages are high a leak of a few hundred kilo ohms can have a significant effect. I guess valve enthusiasts would have spotted the problem much earlier!

I replaced the paper capacitor with a 0.047µF 400v polyester ‘mustard’ type often used in Marshall amplifiers. The voltage across R5 dropped to normal at 6v and current consumption reduced. More importantly the HT voltage from the module remained steady at 229v.

Emerging from the rabbit hole

With much lower current the radio worked well on FM. On AM not so well, with excessive whistles and interference between stations. I suspected the high voltage inverter module and the scope confirmed it was generating the interference due to its switching frequency – much higher than the 115Hz electromechanical vibrator.

Even when assembled in its metal casing, the interference persisted and to make matters worse the HT module ran hot. The IR camera showed peak heat spots exceeding 80 degrees after several minutes. After twenty or so minutes the new relay cut out. This seemed to be another game of whack-a-mole (I have nothing against the humble mole) but my rabbit running was testing my patience!

I monitored the current consumption on the high voltage side and this was well within the module’s rating. Tuning the module’s output down to 200v still resulted in it cutting out after running for over 15 minutes so I concluded it needed a fan to sustain the Becker’s demand.

But why would the new relay also fail? The IR camera showed the relay’s temperature one end approaching 40℃ so it too was suffering from heat. The circuit diagram shows a 35Ω series resistor, R4, so I wired this back in place for the new relay. This reduced the relay’s temperature but it occasionally appeared to cut out.

After several patient hours spent listening and monitoring the radio’s vital statistics it dawned on me the problem pointed to the HT module. It would suddenly cut out, the Ht voltage would drop to zero but the valve heater still glowed. It wasn’t the relay now causing the radio to stop functioning it was lack of high voltage.

Back down the warren again

I needed a new approach. Integrating new semiconductor technology inside a valve enclosure would never go well. There’s simply too much heat. At least the high voltage module proved the radio worked but I needed to restore the Becker’s power supply the way it was originally designed.

Perhaps the aged electromechanical vibrator could be made to work? I hooked up a 12v supply to its input pins and listened carefully. There was a faint buzz I’d not noticed before, expecting it would make more noise. I connected some low value resistors in series with its switching contacts and checked the output on the oscilloscope. All looked good. It had a 40/60 mark space ratio with only small glitches as it switched on and off.

I decided to remove the high voltage module, re-installed the bridge rectifier and plug the metal can back in place. Disaster, it consumed over 10A peak and the fuse popped.

There must be another fault I’d not spotted. I checked the transformer windings and the secondary seemed lower resistance than the primary. How could this be, was the transformer’s secondary short circuit after all – I’d never find another?

Then it dawned on me, doh. On the circuit diagram there’s a suppressor capacitor across the secondary winding. It’s rated at 750v and likely to have gone short circuit. It had. I replaced it with a modern X2 plastic film capacitor rated at 630v working and 2.4kV peak. It was hidden under the vibrator below the transformer and threaded through, as shown below.

Success at last, with a new suppressor and many of the capacitors replaced the radio buzzed into life running on old technology. A full soak test for over 1h confirmed the radio was working perfectly once again.

On medium wave the electromechanical switch still generates some inter channel buzzing but with a good aerial station reception is clear. Noticeably quieter than the high voltage module’s interference.

Fault and repair summary

Here’s a summary of the faults and the remedies that worked for me. Your mileage may differ so bear this in mind if the all suggestions fail look for similar instances that could be to cause.

1. Relay contact oxidation – clean relay contacts (this was optimistic given it’s a open framed device).
2. Relay cutout after 10 minutes – replace relay, ensure contact rating is at least 8A DC
3. Tubular electrolytic capacitor overheating – replace in PSU and radio with 47µF 450v, low ESR types
4. Axial electrolytic capacitors in radio – replace all due to component age for reliability. Best use axial leaded capacitors as there’s no circuit board.
5. Paper capacitor current leakage – replace with 400v polyester film capacitors.
6. Axial electrolytic capacitor high ESR in PSU – replace with 100uF 63v
7. Suppressor capacitor short circuit – replace with X2 rated plastic film type.

Footnotes

Useful links

Note Becker produced several different Europa versions including the later TR transistorised versions. The letter acronyms such as LM, MU, etc refer to the wavebands so LM has LW & MW while MU is MW and FM (VHF). Wiring diagrams and schematics for many are available for free download from the excellent Radio Museum site.

• List of Becker models available from Radio Museum – https://www.radiomuseum.org/m/becker_d_en_1.html

• Radio Museum schematic (MU export model) https://www.radiomuseum.org/r/becker_europa_mu_3.html

• Radio Museum circuit diagram (LM model) – easier to read PSU https://www.radiomuseum.org/r/becker_europa_lm.html

High voltage inverter modules

Using a high voltage switching module to generate the 240v valve HT from 12v car battery helps test the radio’s functionality if your HT circuit has failed.

Finding a high voltage module that could permanently replace a faulty electromechanical vibrator is more difficult given the high ambient temperature inside the Becker’s power supply. I can’t recommend the module I used although it allows setting a preset output voltage. The module overheats and consumed higher current than needed and a second one I tested also suffered from instability and would not start once hot. The model I used is designed to charge capacitors and required fan cooling to operate at sustained 40w power output the Becker demands.

It’s possible to replace the electromechanical vibrator with semiconductor switches. I tried one 50Hz square wave generator module designed to drive mains transformers in reverse. Unfortunately it was unsuitable as it generated +/- 12 v i.e. 24v peak to peak instead of 12v. The Becker’s transformer does have various windings on the primary (low voltage) side but the phasing is incorrect. You could probably replace the transformer with a modern mains transformer with a 24v secondary but I did not have one to try.

Vintage capacitors

Go ahead and replace all the electrolytics even if they appear to retain their capacitance. I measured several capacitors that had much higher ESRs than new ones although their capacitance was often higher than marked.

Given the high voltages involved replace all the paper capacitors as these will surely fail. Replace with polyester types for reliability.

Suppressor capacitors suffer from high voltage transients and often fail due to age. Modern metal film types are more reliable. Could add a 10-47Ω series resistor to help absorb current spikes and reduce stain on the capacitor.