Beolit 1000 converter.

[tommytwo]

Hello everyone, my first post since joining the forum.

I own a Beolit 1000 bought new by me in Denmark in 1970. It has worked perfectly for 49 years until recently. I traced the fault to the power converter which raises the input voltage from -7.5 volts DC to +26 volts DC output. The coil in the converter is broken and a replacement coil is not available. I am unable to rewind the the coil as I lack the skill and have poor eyesight anyway.

I would like to replace the converter with something more up to date that fits in the box, which measures 5x7 cm by 18mm deep. Can anyone suggest where I can source a suitable replacement unit and a supplier? I do not intend to ever sell this radio so originality is not a consideration for me.

Thomas.

[toshiba tony]

This radio certainly is unusual. Data on it seems scant but if as you say it ups the input voltage that makes it even more unusual. Upconverters certainly are rarer than than the other way round. Your best bet is probably to approach somebody clued up on such things. Cost would be minimal, indeed the biggest cost will be transporting it. I'm an ex tv engineer of 50 years and only recently left the trade but I'm in Lancashire. I'm sure you would find someone nearer but if not get in touch.

[toshiba tony]

What on earth have you got here, a portable capable of producing 7 watts! It looks a beast. Certainly worth sorting. I have always had a soft spot for B&O gear, even their mediocre gear is ok. Some people say its average gear made to look the part but this radio sounds to be something different. Good luck with it. They are silly money to buy, and rare.

[Station X]

There's a thread here which mentions the convertor:-

https://www.vintage-radio.net/forum/...ad.php?t=83430

I believe the circuit is available from rm.org.

[toshiba tony]

Thanks Graham, I see he is new to the site. It would be good to get him up and running. New model on me but I'm not as up as I used to be on receivers. Sounds a right piece though.

[toshiba tony]

Bored stiff waiting for the pub to open, am I allowed to offer a repair service for his psu. Been in the trade 50 years. If so I'll contact him, cheers Graham.

[Station X]

Yes Tony. You can offer to repair the set for the OP,

[tommytwo]

Thanks to all you gentlemen for the responses to my first post. As I said, I have had the Beolit for 49 years and it has travelled many places overseas with me. I was in Israel for 4 months at the time of the India/Pakistan shindig. I remember hooking the radio up to a 10 metre piece of wire that I found and listening to the war progress on short wave, the signal was very clear. The Beolit, for those not familiar with it, has a short wave expander on the FM tuning and this makes tuning in to the a narrowest short wave frequency very easy. If this radio comes your way, snap it up, it is regarded today as a design classic, and they seem to go for good money when available. I have the manual and a circuit diagram. I recently had to renew the FM side tuning cord and I found that 1mm waxed tuning cord, found on Ebay, did the job admirably.

The radio runs on 5 D cell batteries and will work until the voltage falls to 3 volts. I am told that the coverter circuit converts the DC input to a sine wave, using two MPS 6518 transistors as an oscillator, and then rectifies it back to DC, half the wave via an OA91 diode and the other half via a ZF27 diode. I am not an experienced radio engineer but the converter design looks quite ingenious to me.

I have ordered a module that converts 2/24 volts DC to 2/28 volts DC from Malaysia. If it works, I will regard it as a cheap fix, cost was £3.36. The part is very similar to the origonal converter, which I shall persevere with and fix at my leisure. My idea was to fix it inside the metal box but it may get hot in there so I will attach it to some kind of Tufnol plate for cooling purposes. Once the wood panels are on, it will be invisible anyway.

To conclude, I now find myself visiting this site on a daily basis, there is so much of interest to me here. I especially enjoyed reading about all the "works modifications" that peple have done or come across. Thanks again.

Thomas.

[Graham G3ZVT]

I was going to suggest using one of those Chinese boost converters, I have a selection of boost and buck converters and very useful they are too.

I am sure it will work in your application, but it may generate too much RF noise.

[Mike. Watterson]

A modern DC converter should run cool. The 26V is only for the varicaps? But I could be wrong.

[alanworland]

Thomas you have no doubt read my post regarding my Beolit 1000. Mine was a simple fix but I agree with you that they are fantastic sets, don't use mine as much as I used to but really enjoy it when I do.
I usually use it with the B&O power supply that was sold to go with it.
Like you I bought mine new and it cost me £68 back in 1969/70, a lot of money back then!
Hope you manage to return yours to working order - keep us posted.

Alan

[tommytwo]

Alan, I also looked at your posts when doing my rersearch. I presume you have the manual and schematic for your set, they are easily found via an online search.

My radio cost me 1000 Danish Kroner in 1970, about £70. As you say, a lot of money back then. I got a bit knocked off because a battery had leaked and begun to corrode the negative end, spring in the compartment, easily fixed. I had asked the dealer if he could get me the B & O 700 model but when I went back after 2 weeks, he said he had not been able to source one and offered me the Beolit instead. In those days, I did not realise what a brilliant radio it would turn out to be and I certainly did not think I would still have it all these years later. I just have a stabilised power adapter for it, not the B & O model.

It failed first on not running on batteries, but worked OK on FM with an adapter. Then it refused to work on the AM bands. I discovered that the power supply would only give 21 Volts. Replacing the ZF27 Zener brought me back to 28.5 volts which the trimmer would not bring down. Then I made an error and broke a tiny wire on the coil. This wire is only 0.15mm thick, dark red fabric covered so possibly only 0.10mm thick, so was hard to see anyway. I have Red and Green colour perception problems (Colour Blindness) It proved impossible to solder the wire and a new coil is not available. Hence why I have chosen the option to source a complete new power supply. Without a stable power supply, I cant even think about tracking down any other problems the radio may have.

I will post again when I have some progress to report.

Thomas

[MotorBikeLes]

Let me throw in a "left field" idea, but no idea if it would work or not. I have a NordMende Globetrotter 808 which also uses the high voltage varicaps so likely very similar.
However, 30 years ago I spent a while repairing Samsung CD players, many of which were combined with radios. These had varicap tuning, but since the units operated from mains or batteries, without a high voltage generator the varicaps used were much lower voltage, probably around 5v or so.
Is this a possible route to an solution?
Assuming this idea is dismissed, consider the old ultrasonic remote control handsets. That for the Grundig 6010/6011 etc. used a single "D" cell to generate about 80v for the "loudspeaker" bias. Modifiable maybe?
Les.

[Mike. Watterson]

All varicaps need a higher voltage to get smaller capacitance. It would be nightmare to align. Small, efficient, regulated inverters for battery to 25 to 30V are simple and off the shelf too.
The Samsung radios are unlikely to have used only 5V for the varicaps anyway.

[tri-comp]

The LT1613 Boost switcher is simple to use and readily available (Mouser etc.)
See the attached datasheet and application notes.
It requires less than 5mA quiescent so should be OK with batteries.

rgds,

/Torben

[tommytwo]

Mange tak, Torben. Jeg boede i Danmark 1969-1973 og kan en smule Dansk endnu. Jeg savne den tid. Danskerne er et rar folk.

Thanks for posting the LT1613 data sheet, I will look into that. I am awaiting a power module from Malaysia at the moment, and I hope that will solve my problem. If not, then the LT1613 may be a good option.

Thanks again.

Regards. Thomas.

[tri-comp]

Hej Thomas,
Du skriver rigtig fint på Dansk, efter så mange år.
Impressive

I hope you'll be successfull in repairing the old Beolit-1000.
The speaker is the only really weak point in these as everything else should be fixable.


Med venlig hilsen,

/Torben

[tommytwo]

The power supply that I ordered from Malaysia arrived today, was adjusted off the radio to give the required +26 volts, was fitted and works fine. I am now back to where I started with this radio, before I so unwisely tinkered with the old coverter and broke a tiny induction coil wire. The radio works fine on the FM section, the 3 FM presets work fine and it does not drift off station. It does seem slightly down on volume. I still cant get it to run off batteries. (it uses 5 D cells). In addition, the AM section will not tune any stations, although at full volume, I get a hum through the speaker.

I do not have any specialised test equipment such as a Signal Generator or a Scope, it would ge a steep learning curve for me before I could use them and understand any test result obtained. I only have an Avo 8 meter and a digital meter to hand.

So advice as to where to proceed from here would be gratefully recieved. I shall be studying the schematic tonight looking for clues.

Thomas

[Studio263]

The original converter in the Beolit 1000 is a resonant one, it works using sine waves and its output is stabilised by changing the amount of power which enters the resonant circuit. It can't produce much power, but then it doesn't need to as it is only used to provide the tuning bias voltage.

Modern DC-DC converters use switch mode techniques, which work with square waves. They are efficient and have an amazing power density but they also produce harmonics absolutely everywhere and it takes a lot of skill and knowledge to integrate them properly into existing radio circuitry. This is probably why the AM part of your set no longer works, it is swamped with noise from the converter.

The best (only?) thing to do is to repair the original DC-DC converter in the set properly. In the end its only rewinding a coil, which is hardly a difficult thing to do. I had a similar problem with my own Beolit 1000, when the MW oscillator coil went open circuit (one of the wires had corroded away). In taking it apart I broke a few more, but after an hour or so of fiddling it was all fixed and the set worked perfectly again.

These are valuable sets in clean / original condition, but unresolved repairs using the wrong parts reduce them to the status of being suitable only for parts in my view. It is something to think about.

[tommytwo]

I am happy to report a big success with my Beolit Radio. I spent 2 or 3 hours today cleaning up the circuit board tracks and comparing what I could see with the schematic. Anything iffy, I resoldered and made sure that nothing was being bridged that should not be.

When I plugged in the power adapter, the volume was so loud that it was painful. The AM section has also revived, I got a station on Medium Wave and 1 on Short Wave 2 at around 17.4 Mhz. It is likely that I had some dry joints or had components that were bridged.

The FM section now works without problems. The AM section has a lot of crackling, hissing, and motorboating. When changing the wave bands, there is a lot of crackling so the switches could do with a dose of Servisol, which I dont currently have.

This radio has been my first attempt at reviving something that was dead. It has been a frustrating experience but when one achieves some success, its a great feeling. Some way to go yet but I will get there.