Early 1970’s B&O Beolit 700 resurrected

[Steph Aureus]

I’ve just resurrected my late parents’ old Bang and Olufsen Beolit 700 – a radio I remember them buying with great fanfare in Brighton in 1972/73, and with which I grew up (at least through my teenage years). It seemed to be constantly on, tuned to Radio 3 on FM, and I always remember thinking it sounded good and loving its cool, minimalist Scandinavian designer looks.

Well, 50 years on, it turns out that it had been stuffed into the back of a cupboard at some point after my folks had moved house, and was in a very sorry-looking state. The tuner cord was broken and it was covered with multiple layers of kitchen grease and grime, plus a generous spattering of what seemed to be white paint on the originally black front and rear plastic panels. The telescopic aerial was broken around half way along its length – meaning that the top part and its Beolit-unique end-cap was missing. The original cardboard battery tube had also disintegrated. But despite this, plugging into the mains and turning it on revealed that it was still working, after a fashion, although it did have a nasty mains hum and tuning was difficult (directly turning the tuner capstan on top of the FM box).

Because I don’t like to see stuff chucked out if it can be brought back to life – and particularly not for such an iconic piece of industrial design – I decided to try to restore it. First off, I dismounted the exterior panels, the aluminium end-pieces and beautifully extruded aluminium top piece (with its fascinating ‘Vernier’ tuning mechanism with captive ball bearing indicators) and gave these all a thorough overnight soak in detergent solution, followed by a good scrub with an old paint brush. That got rid of most of the grease and grime. The paint proved harder to shift, but eventually it came off (some foaming car-trim cleaner helped here). Likewise, car-trim plastic shine did a good job of bringing back some lustre on the panels once clean. I also renewed the (disintegrated) foam trim around the speaker at the same time.

Next, I turned my attention to the electronic side. I assumed that the mains hum must be from a failed 1000uF smoothing capacitor in the PSU, so replaced this with a modern Vishay axial part. That did indeed fix the hum – but I think that was probably more a result of a dry solder joint I encountered whilst doing this, rather than a failed cap per se (it actually looked OK, although I don’t have a cap tester). I decided, having embarked on recapping, to replace all the other aluminium electrolytics – even though they were probably still OK and had no signs of physical leakage. There aren’t that many – just one other 1000uF axial rail decoupling cap, two 470uF radial caps (one of which is the AC coupling/ DC blocking cap for the output stage to the speaker) and one 22uF radial cap. I replaced these with standard, good quality Vishay, Rubycon and Panasonic parts of identical capacitance value but moderately uprated voltage. All the other electrolytics in the Beolit – at least mine – are tantalums and can be assumed not to have degraded. Testing again at this stage revealed that the T0.4A slow-blow fuse in the power supply had spontaneously blown, due to age (50 year-old fuses have a habit of doing that, owing to the cumulative effects of minor thermal stress each time the circuit is energised/de-energised) so this was also replaced.

The 50Kohm plastic-bodied Preh-branded sliding volume pot was noisy, so I squirted some Servisol into it. Unfortunately this had the effect of making its action very ‘grabby’, so I resorted to opening it up (the two plastic halves need to be separated with a knife blade). Once disassembled it was relatively easy to clean the tracks and sliding contacts and to carefully regrease the slider mechanism and the transparent plastic tape that curtains the insides against dust ingress. The two plastic half-shells could then be carefully snapped back together and all worked smoothly again. This seems to be the only possible solution, as these sliding pots are no longer available.

Replacing the tuner cord proved to be quite fiddly (getting enough tension on the spring while winding the cord round the capstan) but it was eventually achieved accompanied by the requisite amount of effing and blinding. Note that the 82 cm length stipulated in the Beolit manual proved to be an underestimate and I needed close to 86 cm working length to be able to install and tension it. The aerial was a bit more of a challenge and I bought a cheapo generic telescopic from a well-known online retailer with the aim of lashing up a sort of hybrid affair, using the base part of the B&O one, with its unique detented knuckle, and fusing on the telescopic part from the replacement. Some hacking around with a junior hacksaw and lightly centre-punching the outermost tube back over the original B&O knuckle delivered the desired result (or close enough – at least until such time as I can procure a genuine B&O replacement with the correct top button, maybe from a ‘parts’ Beolit). At this point I also adjusted the DC mid-point of the output stage and checked the quiescent current – all seemed close to spec.

Thus finally came reassembly and testing. And, hey presto, it’s in great song and looks fantastic again. The sound quality on FM absolutely knocks the socks off any of our other portables (on FM, DAB or internet) – all of which sound dull, boxy and muffled by comparison. It’s a pleasure to own, listen to and look at: an absolute design classic!

[newlite4]

Well Done on restoring one of these, they are not for the faint hearted. As a "designer radio", the construction is very unusual and often replacement cabinet parts have to be home made. Biggest problem with these is the very slimline speaker which can jam if the output transistors decide to go short circuit. That said, in good working order, as yours now seems to be, they are simply unbeatable and are well worth the high asking price as vintage items.
Neil

[Ted Kendall]

Nicely done. What grease did you use on the sliders?

[m0cemdave]

I still have the 600 (battery only) version - It cost me a whopping £39.95, or about a week's wages, from Beaver Radio in Liverpool in 1975 - and still consider it to be the best sounding trannie I've ever encountered. It's been carefully maintained over the years (including new electrolytics after 40 years) and still works well.
The only annoyance is that the aerial no longer slides down the tube, with around zero chance of ever finding a replacement.
The limited FM coverage doesn't bother me as it covers all the stations I listen to.

[Steph Aureus]

Sorry, I should have been clearer. I was careful to avoid putting any grease on the tracks themselves (they didn't need anything). The 'sticky' part was the interface between the red plastic potentiometer slider (that the aluminium-cased volume control slider engages with) and the grooves in each half of the grey plastic casing; that's where I carefully applied a small amount of ordinary lithium grease, and just the smallest smear on the transparent plastic 'tape' the screens the innards from dust and moves with the red slider.

[Steph Aureus]

Originally Posted by newlite4

Well Done on restoring one of these, they are not for the faint hearted. As a "designer radio", the construction is very unusual and often replacement cabinet parts have to be home made. Biggest problem with these is the very slimline speaker which can jam if the output transistors decide to go short circuit. That said, in good working order, as yours now seems to be, they are simply unbeatable and are well worth the high asking price as vintage items.
Neil

I've no intention of selling it. It's much better than any 'dumb speaker' one could buy, and just as flexible in that it has a DIN AUX socket to which one can feed output from (e.g.) a phone. Useful if/when analogue broadcasts do ever get switched off...

[Steph Aureus]

One thing I should probably add / clarify is that I used neutral detergent (washing-up liquid) for soaking the aluminium parts of the case work. That's important, as alkaline detergents (such as washing powder) will attack aluminium and pit it, even anodised aluminium as used on the Beolit. Mildly alkaline detergents are OK for the plastic parts (including the front and rear panels), however.

[Andrew2]

WHAT a beautiful radio they are, I've always fancied one.

[Steph Aureus]

Originally Posted by m0cemdave

I still have the 600 (battery only) version - It cost me a whopping £39.95, or about a week's wages, from Beaver Radio in Liverpool in 1975 - and still consider it to be the best sounding trannie I've ever encountered. It's been carefully maintained over the years (including new electrolytics after 40 years) and still works well.
The only annoyance is that the aerial no longer slides down the tube, with around zero chance of ever finding a replacement.
The limited FM coverage doesn't bother me as it covers all the stations I listen to.

The 'hybrid' aerial I lashed together works well enough (fully retracts and extends), albeit that it lacks the correct top cap. In order fully to retract, the knuckle section has to overcome some sprung-ball detents within the bottom tube - is this the problem area in yours? Mine was still in good working order in that respect, thankfully.