B&O Beovision 600 - UK Vintage Radio Repair and Restoration Discussion Forum

Studio263 · 25th May 2014, 9:03 pm

I was given this set at Mikey 405’s TV Junk Swapmeet by forum member Bobby Ball, who had bought it for a nominal sum to save it from becoming landfill. It is a Beovision 600, B&O’s first fully transistorised TV set and was introduced in around 1972. They are a 17” portable model which use the same tube as the familiar Philips G17T320, although the cabinet is much smaller. There was also a 24” version with a similar chassis, the Beovision 1600, but I’ve never seen one of those.

Most of the first generation solid state monochrome chassis from Europe and Britain gave their far amount of trouble and the B&O is no exception. Funny how none of the manufacturers had much luck with big transistor monochrome sets, but all seemed to be hot running, unreliable and short lived. Adherence to thick necked tubes which required a lot of scanning power now doubt had a lot to do with it, but all caused a lot of aggro when compared to the absolutely dependable generation of small screen Japanese sets of the same era.

The little B&O uses quite a bit of odd circuitry which owes quite a lot to valve practice. Most significantly as much of the set as possible is run from a stabilised 180V rail, including the line, frame and sound output stages, the latter requiring the use of a special 800 ohm loudspeaker. This rail is derived from the mains, which is rectified and then stabilised and smoothed by an “electronic mains dropper” circuit which consists of either two power transistors in series or four in two series – parallel pairs, depending on the version. This one has two, but there are places on the PCB for the others. These transistors are shunted by a conventional high wattage resistor which provides a bleed to start the circuit up and is tapped at its mid point to enable the transistors to share out the voltage in a “totem pole” arrangement. An isolated winding on the LOPT provides a 60V boost to make 240V for the video output stage (see diagram below), 1D5 is the rectifier for this and it can be seen that the other end of the winding (part of the LOPT, note the overwind next to it, the rest isn’t shown here) is returned to the 180V rail. This supply is also used to control the regulator; since it has no hum in it it makes the “dropper” transistors act like an active filter so there is very little in the way of conventional smoothing in the rest of the circuit. Regulation acts so that the output of the line stage stays constant with the 180V rail being adjusted to compensate for changes in mains voltage, beam current etc. Because of this stabilisation it is possible to DC couple the video stages and gives accurate control over the black level of the picture without risking damage to the LOPT, which was a problem with some other sets which tried to do the same without having accurate EHT control. As with the Philips 320, the power supply does not give full output until the line output stage starts up, although this is done in a different way.

To take advantage of the possibility of providing an “instant picture” from the transistorised circuitry the tube heater of this model is left running all the time, receiving 4.2V AC even when the switch is off. It really does work and fortunately these 17” tubes seem very durable, although with the 24” ones it seems less of a good idea…

The reported fault with this set was a frame collapse and at first it seemed as if some work had already been done in this area. However, most of the affected components were in the regulator, so once this was all tidied up there was still no frame scan. The reason didn’t take long to find, both the height and the linearity control fell apart when touched and when replacements were fitted the frame scan was restored. This revealed a lack of width and an odd-shaped single (50 Hz) hum bar, whose magnitude varied with picture content. The “set HT” control worked but even at maximum could only provide 155V instead of the correct 180V. The chassis was running warm but not excessively so, so I decided that there must be a fault with the power supply rather than something else dragging things down. As it is easy to reach, my first port of call was the main reservoir capacitor 2C6. It is supposed to be 250uF but it only read about 170 so I replaced it with a 220uF one from a TX10 with an extra 22uF in parallel. This made no difference at all, other than causing the single rectifier diode 2D1 to fail high-resistance shortly afterwards. This produced the oddest shaped raster that I’ve ever seen, like a squat wide-mouthed vase whose opening was approximately in line with the centre of the screen. I didn’t leave the set on long enough to take a picture as it didn’t look at all healthy, a new BY127 to replace the too odd diodes twisted together that the last person put in cured it though.

Back to the hum bar. All the large parts of the circuit (transistors, resistor 0R1 etc) were checked and found to be OK. The picture itself was pretty reasonable other than the hum with loads of contrast and rock steady sync so I felt that the fault had to be in this area somewhere. Then I did what I should have done from the start, check the 240V supply to the video stage. It was low at roughly the same reduced voltage as the main HT rail, with the voltage across 1C61 close to zero. At first I suspected that either 1R98 or 1D5 must be open circuit but they were fine, the real culprit was 1C61 which was open circuit and when removed proved to have a big crack in its side. It is often the case with circuits that rectify pulses of a short duration that when the relevant capacitor fails the DC level of the output falls to near zero and in this case a new 4.7uF 100V electrolytic brought the 180V supply back up to normal and a returned a solid, hum-free picture. It is important with these sets to set up the “set HT” control using the exact method that the service sheet specifies since it is the line output stage power and not the supply voltage which is stabilised, getting it wrong can damage the line output transistor, the transformer and the insulation around the EHT rectifier stick.

I had a look around and found a few more capacitors of the same type as 1C61. Another also read practically open circuit so I replaced the lot; this resulted in a set which gives outstanding performance and one which has so far proved to be stable and reliable. The tube is very good and the high level of picture and sound quality make it a joy to watch.

Note that the attached circuit is taken from the Beovision 601 manual, which is a similar set although there are seemingly endless detail changes. I’ve done this because all the 600 / 1600 diagrams I have show the 4 power transistor version, even the one which is still in the original envelope inside the set and shows the correct type number. The 601 circuit is correct for this set although the component reference numbers are different.

marsbar · 26th May 2014, 2:55 am

Lovely set, hope you manage to repair it? If you do, I suggest you install a computer fan from an old computer psu. Use a 7808 to lover speed from 12v, thus making the fan silent. I did so in an old bo, because it got to hot inside, burning all components. Went from hot hot hot to room temp on aall components!

bobbyball · 26th May 2014, 10:31 am

I knew when I saw this set advertised locally that it had "a certain person's" name on it and needed to be saved. Considering the tube is 17" it is a very compact thing and not excessively heavy given the unusual circuitry contained within.

At the time, and with colour sets still very expensive, the black and white set was still very popular, and needless to say this offering from B&O proves the point as they clearly thought it worthwhile to introduce such a set. Nice work as ever!

Nickthedentist · 26th May 2014, 3:17 pm

Quote:

Originally Posted by marsbar

Lovely set, hope you manage to repair it?

Studio263 can mend pratically anything, and has already fixed this, if you look carefully:

Quote:

Originally Posted by Studio263

...this resulted in a set which gives outstanding performance and one which has so far proved to be stable and reliable. The tube is very good and the high level of picture and sound quality make it a joy to watch.

Nick

marsbar · 27th May 2014, 1:56 am

I am jealous, I also want a B/W TV.

Studio263 · 27th May 2014, 7:35 am

Quote:

Originally Posted by marsbar

I suggest you install a computer fan from an old computer psu.

I encounter modifications like this from time to time and I always remove them on sight, such things should not be necessary if the set is working correctly and positioned in a suitable way. B&O always include in their user instructions a diagram showing minimum clearances around the set with are required for normal, reliable operation and these should be taken as an absolute minimum. Keeping the chassis clean and the various slots in the cabinet clear of dust also helps. Fans seem to draw in a lot of muck which can make the problem worse - look inside a computer of any age and you'll see what I mean!

I've seen some really lethal mods, including fans powered from the isolated side of the power supply attached to things on the "mains" side with no additional protection, the possible consiquences don't bear thinking about...

Some of the early B&O sets run hot in the UK because of the measures taken to deal with our "high" mains voltage of 240V (which it still is here most days). Additional resistors were added to drop the surplus 20V, which in the case of the 600 means 8 more watts to get rid of in that tiny cabinet somewhere. Still, it seems superbly designed and it copes well. Models with 20AX tubes (4402 etc) and later all use so little power that the backs hardly get warm so no issues there.

Hottest running set we ever had: Grundig 1510GB portable, you couldn't touch the back after a few hours of use. I wish I'd kept that but the tube (14" Toshiba RIS) was dead flat, has anyone seen one recently?

gec2110 · 27th May 2014, 12:05 pm

Very nice set and in such good conditon as well
any chance of a photo of the set working
i remember these were capable of a good monochore picture and sound

Studio263 · 28th May 2014, 6:54 pm

Quote:

Originally Posted by gec2110

any chance of a photo of the set working

Your wish is my command! I've pulled the scans in a little so that it is clearer how good the geometry is. Appologies for the reflections, believe it or not out of 10 photos this was the best (least rubbish) one...

Set is a cracker.

marsbar · 28th May 2014, 8:35 pm

Neat! Often heat can be a problem in products. I guess a bw tv stays cooler than a colour since colour tv has 3 times the components and thus 3x the power consume...

I have had so many items gone to trash because of poor design due to heat. Like keeping a circuit board horizontal with no air flow when it should be vertical to let air pass all components instead of locking it in... in some cases the pcb is brown and black of heat.

Computers indeed need a fan, and also regularly cleaning by high pressure air once in a while to get rid of dust. Everything need maintenance!

Synchrodyne · 29th May 2014, 1:35 am

Excellent! It reminds me that when I lived in London in the later 1970s, I had a B&O 24 inch monochrome TV receiver that also delivered an excellent picture. I bought it from a local shop in Ealing Broadway; I think that it was NOS after the model had ceased production. The chassis was Type 3806 – I kept a copy of the schematic - and I think that the model was Beovision 1601, but I am not sure about that. Something I recall is that one could easily set the black level to where it should be with the brightness control, and then it would stay put. The brightness and contrast controls did exactly what they were supposed to do, with no material interaction, unlike some valve-era TVs, where the black level tended to drop as the contrast was turned up. Also, it had very good sound. I gave it away to a friend when I left London, after having fitted the accessory audio tape recording unit; the DIN socket was already in place, it was only necessary to fit the isolating transformer and wiring. This delivered an output that I reckon was around 100 mV at full modulation, a bit low to fully load the auxiliary/line inputs of typical amplifiers of the period. But I guess that it would have been fine for many tape recorder radio/line inputs.

Cheers,

Studio263 · 29th May 2014, 7:17 am

Type 3806 was the Beovision 1600, the 24" version of this set. Logically there could have been a 1601, based on the 601 chassis, but if there was I have no record of it so I think that it probably wasn't made. The same goes for the Beocenter 1700, which logically should have been a combination of the Beomaster 901 receiver and the Beogram 1100 turntable. This certainly was not produced, even though a gap in the numbering exists for it.

The black level performance of the Beovision 600 is partly down to a neat little trick where the bottom end of the contrast control is returned not to the chassis or some other arbitary point but to a DC potential which is equivalent to the black level that the line gated AGC circuit generates, therefore altering the contrast has no effect on this part of the picture. Since the video channel is DC coupled all the way through it is easy to get good performance from this arrangement without the need for elabortate clamp circuits etc.

Years ago in 'Television' there was an article on the 1600 which explained how to replace the linear power supply with a thyristor circuit similar I would presume to that used in the Philips 320, the aim being cooler running. Despite much looking though I've not been able to find it, does anyone know which issue it was in?

gec2110 · 29th May 2014, 1:09 pm

That is a good picture

Hybrid tellies · 29th May 2014, 8:10 pm

What a set. I never came across the this B&O set but it looks good and nice to work on. Really enjoyed your excellent write up.

Synchrodyne · 31st May 2014, 12:32 am

Quote:

Originally Posted by Studio263

The black level performance of the Beovision 600 is partly down to a neat little trick where the bottom end of the contrast control is returned not to the chassis or some other arbitary point but to a DC potential which is equivalent to the black level that the line gated AGC circuit generates, therefore altering the contrast has no effect on this part of the picture. Since the video channel is DC coupled all the way through it is easy to get good performance from this arrangement without the need for elabortate clamp circuits etc.

Quite neatly done, then, and evidently the B&O designers understood the importance of getting the black level right. Thanks for the description.

Cheers,

Okto1984 · 1st Jun 2014, 12:15 am

Looks like a very nice TV. I'm surprised how modern the design is for 1972. One thing is puzzling me though, where does the sound come out of?

Studio263 · 1st Jun 2014, 8:57 pm

Quote:

Originally Posted by Okto1984

One thing is puzzling me though, where does the sound come out of?

Ah, there is a nice big loudspeaker fitted in the rear cabinet shell, even most full-sized colour sets don't have one of this size and quality! Sharp-eyed B&O spotters will immediately realise that the set in this picture is a Beovision 601, but the 600 is very similar.

Maarten · 2nd Jun 2014, 2:30 am

I belive Philips uses this or a very similar speaker in some of their own sets as well.

Studio263 · 16th Jun 2014, 1:00 pm

My appologies to forum member Synchrodyne, there WAS a Beovision 1601! It was sold in France (and possibly elsewhere too) and was, as expected, a Beovision 1600 with the later 601-type chassis.

More interesting than that, there was also a 901 which is like a 601 (similar to the 600 shown here) but with a 20" tube and a different handle. It looks really nice in the picture, curse - I want one now!

The 600 is still going strong by the way, even in this lovely warm weather that we've been having.

25th May 2014, 9:03 pm	#1
Studio263 Octode Join Date: Apr 2007 Location: Hampshire, UK. Posts: 1,578	B&O Beovision 600 I was given this set at Mikey 405’s TV Junk Swapmeet by forum member Bobby Ball, who had bought it for a nominal sum to save it from becoming landfill. It is a Beovision 600, B&O’s first fully transistorised TV set and was introduced in around 1972. They are a 17” portable model which use the same tube as the familiar Philips G17T320, although the cabinet is much smaller. There was also a 24” version with a similar chassis, the Beovision 1600, but I’ve never seen one of those. Most of the first generation solid state monochrome chassis from Europe and Britain gave their far amount of trouble and the B&O is no exception. Funny how none of the manufacturers had much luck with big transistor monochrome sets, but all seemed to be hot running, unreliable and short lived. Adherence to thick necked tubes which required a lot of scanning power now doubt had a lot to do with it, but all caused a lot of aggro when compared to the absolutely dependable generation of small screen Japanese sets of the same era. The little B&O uses quite a bit of odd circuitry which owes quite a lot to valve practice. Most significantly as much of the set as possible is run from a stabilised 180V rail, including the line, frame and sound output stages, the latter requiring the use of a special 800 ohm loudspeaker. This rail is derived from the mains, which is rectified and then stabilised and smoothed by an “electronic mains dropper” circuit which consists of either two power transistors in series or four in two series – parallel pairs, depending on the version. This one has two, but there are places on the PCB for the others. These transistors are shunted by a conventional high wattage resistor which provides a bleed to start the circuit up and is tapped at its mid point to enable the transistors to share out the voltage in a “totem pole” arrangement. An isolated winding on the LOPT provides a 60V boost to make 240V for the video output stage (see diagram below), 1D5 is the rectifier for this and it can be seen that the other end of the winding (part of the LOPT, note the overwind next to it, the rest isn’t shown here) is returned to the 180V rail. This supply is also used to control the regulator; since it has no hum in it it makes the “dropper” transistors act like an active filter so there is very little in the way of conventional smoothing in the rest of the circuit. Regulation acts so that the output of the line stage stays constant with the 180V rail being adjusted to compensate for changes in mains voltage, beam current etc. Because of this stabilisation it is possible to DC couple the video stages and gives accurate control over the black level of the picture without risking damage to the LOPT, which was a problem with some other sets which tried to do the same without having accurate EHT control. As with the Philips 320, the power supply does not give full output until the line output stage starts up, although this is done in a different way. To take advantage of the possibility of providing an “instant picture” from the transistorised circuitry the tube heater of this model is left running all the time, receiving 4.2V AC even when the switch is off. It really does work and fortunately these 17” tubes seem very durable, although with the 24” ones it seems less of a good idea… The reported fault with this set was a frame collapse and at first it seemed as if some work had already been done in this area. However, most of the affected components were in the regulator, so once this was all tidied up there was still no frame scan. The reason didn’t take long to find, both the height and the linearity control fell apart when touched and when replacements were fitted the frame scan was restored. This revealed a lack of width and an odd-shaped single (50 Hz) hum bar, whose magnitude varied with picture content. The “set HT” control worked but even at maximum could only provide 155V instead of the correct 180V. The chassis was running warm but not excessively so, so I decided that there must be a fault with the power supply rather than something else dragging things down. As it is easy to reach, my first port of call was the main reservoir capacitor 2C6. It is supposed to be 250uF but it only read about 170 so I replaced it with a 220uF one from a TX10 with an extra 22uF in parallel. This made no difference at all, other than causing the single rectifier diode 2D1 to fail high-resistance shortly afterwards. This produced the oddest shaped raster that I’ve ever seen, like a squat wide-mouthed vase whose opening was approximately in line with the centre of the screen. I didn’t leave the set on long enough to take a picture as it didn’t look at all healthy, a new BY127 to replace the too odd diodes twisted together that the last person put in cured it though. Back to the hum bar. All the large parts of the circuit (transistors, resistor 0R1 etc) were checked and found to be OK. The picture itself was pretty reasonable other than the hum with loads of contrast and rock steady sync so I felt that the fault had to be in this area somewhere. Then I did what I should have done from the start, check the 240V supply to the video stage. It was low at roughly the same reduced voltage as the main HT rail, with the voltage across 1C61 close to zero. At first I suspected that either 1R98 or 1D5 must be open circuit but they were fine, the real culprit was 1C61 which was open circuit and when removed proved to have a big crack in its side. It is often the case with circuits that rectify pulses of a short duration that when the relevant capacitor fails the DC level of the output falls to near zero and in this case a new 4.7uF 100V electrolytic brought the 180V supply back up to normal and a returned a solid, hum-free picture. It is important with these sets to set up the “set HT” control using the exact method that the service sheet specifies since it is the line output stage power and not the supply voltage which is stabilised, getting it wrong can damage the line output transistor, the transformer and the insulation around the EHT rectifier stick. I had a look around and found a few more capacitors of the same type as 1C61. Another also read practically open circuit so I replaced the lot; this resulted in a set which gives outstanding performance and one which has so far proved to be stable and reliable. The tube is very good and the high level of picture and sound quality make it a joy to watch. Note that the attached circuit is taken from the Beovision 601 manual, which is a similar set although there are seemingly endless detail changes. I’ve done this because all the 600 / 1600 diagrams I have show the 4 power transistor version, even the one which is still in the original envelope inside the set and shows the correct type number. The 601 circuit is correct for this set although the component reference numbers are different. Attached Thumbnails

26th May 2014, 2:55 am	#2
marsbar Triode Join Date: Apr 2011 Location: Stavanger, Norway . Posts: 49	Re: B&O Beovision 600 Lovely set, hope you manage to repair it? If you do, I suggest you install a computer fan from an old computer psu. Use a 7808 to lover speed from 12v, thus making the fan silent. I did so in an old bo, because it got to hot inside, burning all components. Went from hot hot hot to room temp on aall components!

26th May 2014, 10:31 am	#3
bobbyball Octode Join Date: Jul 2011 Location: Stockport, Greater Manchester Posts: 1,217	Re: B&O Beovision 600 I knew when I saw this set advertised locally that it had "a certain person's" name on it and needed to be saved. Considering the tube is 17" it is a very compact thing and not excessively heavy given the unusual circuitry contained within. At the time, and with colour sets still very expensive, the black and white set was still very popular, and needless to say this offering from B&O proves the point as they clearly thought it worthwhile to introduce such a set. Nice work as ever! __________________ Robert

27th May 2014, 1:56 am	#5
marsbar Triode Join Date: Apr 2011 Location: Stavanger, Norway . Posts: 49	Re: B&O Beovision 600 I am jealous, I also want a B/W TV.

27th May 2014, 12:05 pm	#7
gec2110 Retired Dormant Member Join Date: Feb 2008 Location: Croydon, London, UK. Posts: 408	Re: B&O Beovision 600 Very nice set and in such good conditon as well any chance of a photo of the set working i remember these were capable of a good monochore picture and sound

28th May 2014, 8:35 pm	#9
marsbar Triode Join Date: Apr 2011 Location: Stavanger, Norway . Posts: 49	Re: B&O Beovision 600 Neat! Often heat can be a problem in products. I guess a bw tv stays cooler than a colour since colour tv has 3 times the components and thus 3x the power consume... I have had so many items gone to trash because of poor design due to heat. Like keeping a circuit board horizontal with no air flow when it should be vertical to let air pass all components instead of locking it in... in some cases the pcb is brown and black of heat. Computers indeed need a fan, and also regularly cleaning by high pressure air once in a while to get rid of dust. Everything need maintenance!

29th May 2014, 1:35 am	#10
Synchrodyne Nonode Join Date: Jan 2009 Location: Papamoa Beach, Bay of Plenty, New Zealand Posts: 2,944	Re: B&O Beovision 600 Excellent! It reminds me that when I lived in London in the later 1970s, I had a B&O 24 inch monochrome TV receiver that also delivered an excellent picture. I bought it from a local shop in Ealing Broadway; I think that it was NOS after the model had ceased production. The chassis was Type 3806 – I kept a copy of the schematic - and I think that the model was Beovision 1601, but I am not sure about that. Something I recall is that one could easily set the black level to where it should be with the brightness control, and then it would stay put. The brightness and contrast controls did exactly what they were supposed to do, with no material interaction, unlike some valve-era TVs, where the black level tended to drop as the contrast was turned up. Also, it had very good sound. I gave it away to a friend when I left London, after having fitted the accessory audio tape recording unit; the DIN socket was already in place, it was only necessary to fit the isolating transformer and wiring. This delivered an output that I reckon was around 100 mV at full modulation, a bit low to fully load the auxiliary/line inputs of typical amplifiers of the period. But I guess that it would have been fine for many tape recorder radio/line inputs. Cheers,

29th May 2014, 7:17 am	#11
Studio263 Octode Join Date: Apr 2007 Location: Hampshire, UK. Posts: 1,578	Re: B&O Beovision 600 Type 3806 was the Beovision 1600, the 24" version of this set. Logically there could have been a 1601, based on the 601 chassis, but if there was I have no record of it so I think that it probably wasn't made. The same goes for the Beocenter 1700, which logically should have been a combination of the Beomaster 901 receiver and the Beogram 1100 turntable. This certainly was not produced, even though a gap in the numbering exists for it. The black level performance of the Beovision 600 is partly down to a neat little trick where the bottom end of the contrast control is returned not to the chassis or some other arbitary point but to a DC potential which is equivalent to the black level that the line gated AGC circuit generates, therefore altering the contrast has no effect on this part of the picture. Since the video channel is DC coupled all the way through it is easy to get good performance from this arrangement without the need for elabortate clamp circuits etc. Years ago in 'Television' there was an article on the 1600 which explained how to replace the linear power supply with a thyristor circuit similar I would presume to that used in the Philips 320, the aim being cooler running. Despite much looking though I've not been able to find it, does anyone know which issue it was in?

29th May 2014, 1:09 pm	#12
gec2110 Retired Dormant Member Join Date: Feb 2008 Location: Croydon, London, UK. Posts: 408	Re: B&O Beovision 600 That is a good picture

29th May 2014, 8:10 pm	#13
Hybrid tellies Nonode Join Date: Jan 2004 Location: 1966-1976 Coverack in Cornwall and Helston Cornwall. 1976-present Bristol/Bath area. Posts: 2,967	Re: B&O Beovision 600 What a set. I never came across the this B&O set but it looks good and nice to work on. Really enjoyed your excellent write up. __________________ Simon BVWS member

1st Jun 2014, 12:15 am	#15
Okto1984 Retired Dormant Member Join Date: Dec 2013 Location: Winchester, Hampshire, UK Posts: 288	Re: B&O Beovision 600 Looks like a very nice TV. I'm surprised how modern the design is for 1972. One thing is puzzling me though, where does the sound come out of?

2nd Jun 2014, 2:30 am	#17
Maarten Dekatron Join Date: Dec 2007 Location: Haarlem, Netherlands Posts: 4,203	Re: B&O Beovision 600 I belive Philips uses this or a very similar speaker in some of their own sets as well.

16th Jun 2014, 1:00 pm	#18
Studio263 Octode Join Date: Apr 2007 Location: Hampshire, UK. Posts: 1,578	Re: B&O Beovision 600 My appologies to forum member Synchrodyne, there WAS a Beovision 1601! It was sold in France (and possibly elsewhere too) and was, as expected, a Beovision 1600 with the later 601-type chassis. More interesting than that, there was also a 901 which is like a 601 (similar to the 600 shown here) but with a 20" tube and a different handle. It looks really nice in the picture, curse - I want one now! The 600 is still going strong by the way, even in this lovely warm weather that we've been having.