You may wonder how a sixty year old transistor radio, manufactured in Britain, can be of interest today? Back in the 1960s Ever Ready batteries, along with rival Vidor, powered the majority of torches, cycle lamps and portable radios. Their blue and orange livery awakes nostalgia and long since depleted batteries from that era are still sought by collectors today. Cardboard boxed examples such as the B126 bell battery can fetch £30 and used as props or skins to hide modern equivalents.
To sell more batteries the Ever Ready company decided to manufacture radio component kits in the 1930s followed by complete radios which continued into the late sixties. You may have seen their popular tan cased Sky Leader in TV series such as Heartbeat. Battery powered transistor radios were extremely popular and the Sky Leader and this smaller Sky Master came with carry straps and car aerial sockets for portability.
These sets could receive both long and medium wavebands offering sports coverage, news and music on the go. In many ways they were the Sony Walkman’s of the day and tens of thousands were sold along with a near endless need for batteries to keep they running. They ran on zinc-chloride cells rather than the longer lasting alkaline technology used today. Rechargeable cells were an expensive rarity so disposability was unfortunately a norm.
Apart from the satisfaction of touching and seeing a past relic, owning a transistor radio from the sixties can offer several other unique benefits. Well, Radio Retro would say that, so let me try to convince you.
Germanium transistor sound
Electric guitars featured in the majority of sixties popular music and groups such as Led Zeppelin, wanted a unique sound. They found adding distortion in the signal path from a foot peddle could add volume and presence. Jimmy Page chose a Tone Bender Mk II and its magic has propelled the humble OC81D germanium transistor into a must have component to create that distinctive sound.
If you open the back of Ever Ready’s transistor radios of that era you will likely find a Mullard OC81D along with a pair of OC81 that provide the audio amplification. It’s that simple – germanium transistor sound. So why all the fuss? Mullard, who were bought by the Dutch electrical conglomerate Philips, produced a range of semiconductor devices to replace their ubiquitous valves. So most UK radio manufactures such as Bush, Ekco and Ever Ready were sold Mullard’s transistor and diode range from their erstwhile valve salesforce.
Ever Ready Sky Master Inside
This technology upgrade from valve to transistor often replaced the valve amplifier with its transistor equivalent leaving other component types unchanged. Transformers were still used in the audio output stages to match higher impedance devices to drive lower impedance loud speakers. This helped create the softer warm transistor sound that evokes memories in those that still encounter it today. In some ways it’s ironic that Jimmy’s fuzz overdrive sound from the Tone Bender has left a harder metallic legacy.
So what happened to germanium devices and why do some recall sixties transistor radios had an entirely different tinny rough sound?
One answer is silicon. Mullard along with its competitors switched to silicon semiconductor technology as it offered superior performance especially at higher temperature and power. Thermionic valves required heaters to produce electrons that allowed amplification. Germanium transistors on the other hand required no heaters but produced heat in operation, so much so that they ‘ran away’ into self destruction. Heat sinks provided some respite, you can see copper tabs to draw away heat from the OC81 transistors in the Sky Leader and Master.
Silicon devices allowed higher powered amplifiers and with them new circuit designs that did away with the heavy, costly transformer legacy from valve designs. Towards the end of the sixties, Mullard published a series of radio and audio designs using their B series silicon semiconductors replacing the O and A germanium series. The OC81 and AF180 were dead.
Ever Ready Sky Master Top Controls
Turn up the volume
So what’s this have to do with the old Ever Ready transistor radios? Well germanium powered radios are not as harsh as silicon at full volume. It’s probably due to a combination of factors the most significant of which is harmonic distortion. Even harmonics such as second, fourth, etc sound smother than their odd harmonics. The difference is easy to see on an oscilloscope.
Amplifiers faithfully track their input signals as the volume is increased until they reach their maximum output. A limit is reached when the amplifier’s voltage output hits their power supply – in this case provided by an Ever Ready 9v battery. The resultant audio waveform is clipped and the sound becomes fuzzy or distorted.
Some sixties germanium amplifier designs such as Bang and Olufsen’s transformerless Beolit range, used germanium output transistors and still sounded excellent.
The mellow sixties transistor radio sound was I feel due to a combination of transformer coupling and low gain germanium transistors. The volume could never really be described as loud even with the volume control turned right up it simply did not have enough oomph.
Silicon however offered higher amplification and with it clipping of the audio waveform as the devices saturated and hit their DC supply voltage. This sounded hash and with the removal of a fluffy transformer output could be heard.
And that’s the irony – Jimmy’s Tone Bender Mk II used a germanium transistor driven hard to create the distortion but its germanium technology produced a softer distortion than a silicon equivalent. So the obsolete OC81D (d is for driver as it was used to drive the pair of OC81s in push-pull arrangement) has become a sought after device to recreate that sound.
The final irony (if you can suffer more) is that sixties transistor radios are being ‘up-cycled’ as modern guitar practice amplifiers to offer that classic sixties sound without the expense of an additional £200 Tone Bender. And here’s an example of a Sky Master doing just that.
So keep a look out for an early sixties transistor radio with its germanium technology and take a listen to the classic sound. Here are some ways you can continue to enjoy the sound.
- Tune in to AM radio! There are still many stations broadcasting on medium and long wave.
- Add an audio input jack or convert a headphone jack to input to use the radio’s amplifier and speaker. To connect an electric guitar it will also benefit from a small preamplifier.
- Add a bluetooth receiver with a separate rechargeable battery (via a USB connector). Note the radio’s battery is not suitable for Bluetooth receivers as they operate on much lower voltages and use a negative chassis / earth unlike many sixties radios that are positive earth.
Try to reuse the original audio amplifier and speaker for an authentic sixties sound. If the amplifier won’t work reliably replace it with a small modern analogue audio amplifier using the original speaker – avoid class D switching amplifiers.
PP7 battery
Although these radios require a PP7 9v battery that’s not easily available there are several options. If you have a colour printer it’s possible to download copies of an original Ever Ready PP7 cardboard box design and make a surround. This can contain 6 x AAA cells or an alkaline PP3 battery. See the excellent VRAT forum for more details – https://www.radios-tv.co.uk/community/dials-logos-batteries/pp7-battery-ersatz-replacement/
Ever Ready Sky Master Rear view
PS
If you want the best chance of a working radio, look for models using the Mullard OC range of black tube transistors or thin silver tubes. Avoid models with the fat round metal capped AF range, like the Sky Master unfortunately chose, as they are prone to an inherent ‘tin whisker’ design fault and unlikely to work as a radio. Alternatively if you just want to use the amplifier remove the AF transistors and connect or rewire an input jack connected to the volume control.
Apologies for strange formatting in this post yet another WordPress update that’s not compatible. May go back to plain old HTML if this continues…
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