I'm absolutely stunned of the vast amount of engineering that has went into the drum assy. Thought it's one big piece of nicely machined alloy, but no, it is filled with dozens of clever solutions down to the smallest room. Each of these solutions would be worth a doctoral dissertation. Wow. Also, I have to tell you that I love your Betacam trilogy, and your channel as a common.
+Max Koschuh Thanks Max. Sony certainly went all out with the design, which reaped them rewards for decades to come as the format developed. I am tempted to see how the later digital versions are different.
Those small magnets on the drum were PG (pulse generator) and FG (frequency generator) magnets, using the coils on the other part of the drum to help with the speed of the drum. Beta machines also had them, don't think I ever saw one on a VHS machine.
Thanks for another great teardown of the machines I used to maintain! They were so expensive and parts were very pricy, too. I think the full drum assembly was around $5,000 USD. The upper drum with just the video heads was about $2,000. Early on, I would jumper across the hours meter battery with a power supply to keep the memory intact, but after a while we stopped caring and just replaced the parts when they failed. The first sensor is an inductor with AC across it to sense presence of the tape leader which is metal. The head near the supply tension arm is the control track head.
Those heads can both change attitude and azimuth. 2 ceramic transducers so it can both go up and down to follow the tape path in trick mode, using a sawtooth waveform to make it follow the new path of the video track, but it also has to twist slightly to get the head gap normal to the path change, so it gets the maximum amplitude of the FM video for best performance. 1800Hz sawtooth waveform per head, with the DT15 boards being the power amplifiers, using those position sensors under the head, to get the timing per head ,along with providing commutation for the 3 phase motor drive and an index pulse. Blue wire is not a dew sensor ( that is provided on the syscon board) but a drum heater, to keep the drum warm when power is applied. The tape path heads are first full erase, then linear audio and tracking ( on top and bottom edges of the tape) and the last 2 are to record and then do the confidence playback of the audio. Auto tape cleaner is engaged at tape load and tape unload, so the video heads are cleaned. There is also a clean done if the video amplitude fluctuates a lot, indicating tape damage, so as to not have oxide shed clogging a record head. Those drums were repairable, using a microscope jig, so you could put in new head tip assemblies to replace worn ones. Worth it as the head was almost half the cost of the machine, so you would typically send it to a Sony Service Centre which would put in a refurbished head ( so you got it back fast), align it then send it back to you, then they would spend a day replacing the head tips and getting the shimming right to put it in stock. You only replaced the drum if it was worn, or if the electronics on it or the rotary transformer failed. Service was pretty expensive on those machines, but as they were the only game in town you paid.
+SeanBZA The blue wire is definitely a dew sensor. There's no drum heater. The heads (upper drum) were very expensive, around $2,000 USD, but nowhere near half the cost of the machine (I think we paid $35,000 for our decks). Lower drums were even more, like $5,000, I think. As you say, they didn't usually need replacing. I never saw refurbished drums from Sony, only new ones. Some other companies may have done refurbiishment.
While working on a BVW 75 recently, the clear plastic high voltage safety cover (already broken) fell away and I put my finger in there by accident while it was in playback. Maybe I got lucky it didn't even hurt really but it was quite a surprise. My brain instantly said '!30 hz!'. Perhaps this was 30 HZ 1/2 duty cycles of said 1800Hz but I don't get readings quite that accurate in this manor. I don't yet know exactly what is supposed to be on those test points but from how it felt I'm guessing something is driving one head at a time, not continuously. At least I didn't put a screw driver in there!
It was 30 hertz. Perhaps SeanBZA meant 1800 rpm which is the drum speed. There are two DT assemblies 180 degrees apart each with a Y and a CTDM head. A low level dither signal was added to the drive signal to improve track following. You're right that only one head is driven at a time except for a brief overlap at head switch time.
I have seen very similar slip rings devices in aircraft gyroscopes. The amount of precision tongue angles needed at the factory to make this drum assembly seems insane. With help of dedicated calibration instruments I guess.
They sure did make those slip rings small. My guess is this is to reduce wear/extend the lifetime. 12 channels and that of course doesn't include the rotary transformer channels! It seems Betacam is the pinnacle of analog video quality and complexity. I've been intimidated by it so I'm only now learning to work on them many years into this.
it is essentially a BETAMAX Video Cassette Recorder in a camera what could be simpler and this is the forerunner to the MiniDV camera system which is a miniaturized version of the BETAMAX, the small coils relay spindle speed information back to the head motor controller as well as the SYSCON board to control the speed of the feed and take up spools.
I always loved SONY for what they did. Open any kind of device from sony its a plaisure. Looks beautiful. The electronic design the mechanical design the precision just fantastic
Micron-level tracking precision...for when the video has to be near perfect as possible. This type of attention to detail is why a new drum alone can cost north of US$10,000.
I wonder what that entire assembly cost to replace? That's some of the most impressive engineering I've seen, the slip ring assembly alone is a work of art.
+ProdigalPorcupine not sure of the cost but the stickers on the video heads might have a date code of week 15, 1993 so it may have been replaced in the past
Upper drum was about $2,000, complete drum $5,000 if I remember correctly. Whole VTR was $35.000. Sony still lists these parts: BRUSH ASSY $292.25 SLIP RING ASSY $768.63
Thank you for such a thorough tear-down. The dynamic tracking heads are the larger assemblies with the piezo transducers. If I understand right, the dynamic tracking heads are for playback only (if I'm wrong I want to know). The reason (again if I understand right) is that because DT heads aren't rigidly fixed in place they might move around during recording as they won't have a track to lock onto (having just been erased). The recording head moving would result in a recording that doesn't have properly curved tracks. Although dynamic tracking on playback might be able to track that, it would not playback well on say, a BVW 70 which only has fixed heads and cannot track uneven tracks. I work on VTR's a lot and have been waiting to work with these things for 20 years and 'just' got 3 of them about 6 months ago and I'm working out how to restore full operation for actual editing. Two of them are in far worse shape then yours there and Betacam is more complex then anything I've worked with yet. so I'm getting useful info from your video that I haven't seen in the incomplete bits and pieces of manuals I have. Always good to see anyone working with these.
In Record mode the DTF heads are applied a fixed voltage relating to the centre of the desired track, to ensure compatability with non DTF machines. The DTF system was also used in the Philips / Grundig V2000 domestic machines. E.g. Vr2020 and 2x4 super. I have worked on these machines for many years and love the diverse engineering not only electronic but mechanical systems too.
+mikeselectricstuff I would think so yes, i did think about this while i was editing, that i should have checked the shim thickness between the two adjacent fixed DT read heads as i think there should be a small offset between them
Beautiful teardown (as much crying I was doing watching you cut this system up). But very nice to see the hidden aspect of design. Again, Sweeeet . Thanks
Thank you for this detailed video. I knew that helical scan systems are complex but I never realized how complex they can get. Questions: 1) Was this piezo tracking feature a necessity in Betacam, or a feature present only in high-end machines? 2) Do they have such tracking in VHS heads? 3) Do the later digital helical scan systems like DAT and MiniDV also use this, or did they eventually find a different tracking method that allows for simpler/cheaper head assembly?
It's hard to say, there are so many systems in so many markets. I would be surprised if any domestic VHS machines used it, but the professional versions might. I have never seen it mentioned on any of the smaller implementations of HS like DAT, this could be due to the width and speed of the tape. Certainly the dynamic tracking was used widely in betacam & digibeta. The Sony D-1 format also used dynamic tracking, i'd love to teardown one of those machines!
Piezo dynamic tracking heads are not needed to record or play back tape, they are for obtaining a clear playback signal at tape run speeds other than normal. This makes still images, slow and higher speed search (2 to 3x normal, possibly more) look very nearly as good as playback speed. Without dynamic tracking heads (AST) the noise bands between video frames would be visible and not correctable via electronic means, although many VTRs can hide the mess by replacing the noise with previous image information. I have seen one professional grade VHS machine that has dynamic tracking but this feature is rare in vhs. The best dynamic tracking I've seen is on 1" reel to reel, Ampex vpr-3, although I believe there were betacam SP decks made with 3x playback. As far as I know, dat and miniDV and many other other (but not all) digital formats rely on a digital buffer to hold image and other information while the tape is not in playback speed but they are able to pick up some information like track data and enough video data to make part of the frame visible. A clean still image is made by storing the last frame played into digital memory before the tape is stopped, some analog machines have a digital frame buffer to do this as well.
Any chance you could sell me the torn down head? I've been reading talk of using the bearing to make a rather cheap turntable bearing. I'd just need the mechanics rather than any electronics.
+nathnullobject If you go to my about page you can access my email, send me a message and we'll see what we can sort out: th-cam.com/users/DextersLab2013about
As themastertrevor comments; All the extremely tight tolerance engineering, technology, electronics and Betamax was said to be better than VHS; now where is it... Even the Tape surface and substrate had Physics breakthroughs... To achieve this. P.S. Spot of dirt on the tape, may jump a bit on playback but keeps going, DVD/BluRays stop died ...
The DTF system was also used in the PHILIPS V2000 VCR with the double sided video cassette, if these numb skulls don't stop butting in I am moving to Linus Media's FLOAT-PLANE.
Nice teardown! The complexity and cost of this design make modern electronics look too easy.
+Applied Science Thanks Ben!
I'm absolutely stunned of the vast amount of engineering that has went into the drum assy. Thought it's one big piece of nicely machined alloy, but no, it is filled with dozens of clever solutions down to the smallest room. Each of these solutions would be worth a doctoral dissertation. Wow.
Also, I have to tell you that I love your Betacam trilogy, and your channel as a common.
+Max Koschuh Thanks Max. Sony certainly went all out with the design, which reaped them rewards for decades to come as the format developed. I am tempted to see how the later digital versions are different.
I was just looking at a Sony DJR-22 dynamic tracking head assembly which I believe was designed for a Betacam SP camcorder. It has 15 heads on it!
douro20 probably betacam sx, that used lots of individual fixed heads. With HDCAM SR there was as many as 32 heads on the SRW-5800
Yeah, this is why those machines are so expensive.
Those small magnets on the drum were PG (pulse generator) and FG (frequency generator) magnets, using the coils on the other part of the drum to help with the speed of the drum.
Beta machines also had them, don't think I ever saw one on a VHS machine.
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Thanks for another great teardown of the machines I used to maintain!
They were so expensive and parts were very pricy, too. I think the full drum assembly was around $5,000 USD. The upper drum with just the video heads was about $2,000. Early on, I would jumper across the hours meter battery with a power supply to keep the memory intact, but after a while we stopped caring and just replaced the parts when they failed.
The first sensor is an inductor with AC across it to sense presence of the tape leader which is metal.
The head near the supply tension arm is the control track head.
Thanks Chris, the head assembly is a work of art!
Those heads can both change attitude and azimuth. 2 ceramic transducers so it can both go up and down to follow the tape path in trick mode, using a sawtooth waveform to make it follow the new path of the video track, but it also has to twist slightly to get the head gap normal to the path change, so it gets the maximum amplitude of the FM video for best performance. 1800Hz sawtooth waveform per head, with the DT15 boards being the power amplifiers, using those position sensors under the head, to get the timing per head ,along with providing commutation for the 3 phase motor drive and an index pulse. Blue wire is not a dew sensor ( that is provided on the syscon board) but a drum heater, to keep the drum warm when power is applied.
The tape path heads are first full erase, then linear audio and tracking ( on top and bottom edges of the tape) and the last 2 are to record and then do the confidence playback of the audio. Auto tape cleaner is engaged at tape load and tape unload, so the video heads are cleaned. There is also a clean done if the video amplitude fluctuates a lot, indicating tape damage, so as to not have oxide shed clogging a record head.
Those drums were repairable, using a microscope jig, so you could put in new head tip assemblies to replace worn ones. Worth it as the head was almost half the cost of the machine, so you would typically send it to a Sony Service Centre which would put in a refurbished head ( so you got it back fast), align it then send it back to you, then they would spend a day replacing the head tips and getting the shimming right to put it in stock. You only replaced the drum if it was worn, or if the electronics on it or the rotary transformer failed. Service was pretty expensive on those machines, but as they were the only game in town you paid.
+SeanBZA Thanks Sean for the extra info!
+SeanBZA The blue wire is definitely a dew sensor. There's no drum heater.
The heads (upper drum) were very expensive, around $2,000 USD, but nowhere near half the cost of the machine (I think we paid $35,000 for our decks). Lower drums were even more, like $5,000, I think. As you say, they didn't usually need replacing. I never saw refurbished drums from Sony, only new ones. Some other companies may have done refurbiishment.
While working on a BVW 75 recently, the clear plastic high voltage safety cover (already broken) fell away and I put my finger in there by accident while it was in playback. Maybe I got lucky it didn't even hurt really but it was quite a surprise. My brain instantly said '!30 hz!'. Perhaps this was 30 HZ 1/2 duty cycles of said 1800Hz but I don't get readings quite that accurate in this manor. I don't yet know exactly what is supposed to be on those test points but from how it felt I'm guessing something is driving one head at a time, not continuously. At least I didn't put a screw driver in there!
It was 30 hertz. Perhaps SeanBZA meant 1800 rpm which is the drum speed. There are two DT assemblies 180 degrees apart each with a Y and a CTDM head. A low level dither signal was added to the drive signal to improve track following. You're right that only one head is driven at a time except for a brief overlap at head switch time.
Thank you for the teardown. Very nice bit of kit, really impressive the amount of effort put in to that piece, alone.
+catt87 thanks, it really is a great piece of engineering.
I have seen very similar slip rings devices in aircraft gyroscopes. The amount of precision tongue angles needed at the factory to make this drum assembly seems insane. With help of dedicated calibration instruments I guess.
+msylvain59 Hand made and trimmed. Tell you what though, i would have loved to see the rigs used during the development of the dynamic tracking heads.
They sure did make those slip rings small. My guess is this is to reduce wear/extend the lifetime. 12 channels and that of course doesn't include the rotary transformer channels! It seems Betacam is the pinnacle of analog video quality and complexity. I've been intimidated by it so I'm only now learning to work on them many years into this.
it is essentially a BETAMAX Video Cassette Recorder in a camera what could be simpler and this is the forerunner to the MiniDV camera system which is a miniaturized version of the BETAMAX, the small coils relay spindle speed information back to the head motor controller as well as the SYSCON board to control the speed of the feed and take up spools.
I was just looking at a DJR-22 dynamic tracking drum head assembly on eBay, which I think was for a Betacam SP camcorder. It has 15 heads!
I always loved SONY for what they did. Open any kind of device from sony its a plaisure. Looks beautiful. The electronic design the mechanical design the precision just fantastic
Micron-level tracking precision...for when the video has to be near perfect as possible. This type of attention to detail is why a new drum alone can cost north of US$10,000.
Roughly the same as Video 2000 DTF?
Sony licensed the V2000 DTF
I wonder what that entire assembly cost to replace? That's some of the most impressive engineering I've seen, the slip ring assembly alone is a work of art.
+ProdigalPorcupine not sure of the cost but the stickers on the video heads might have a date code of week 15, 1993 so it may have been replaced in the past
Upper drum was about $2,000, complete drum $5,000 if I remember correctly. Whole VTR was $35.000.
Sony still lists these parts:
BRUSH ASSY $292.25
SLIP RING ASSY $768.63
There’s gold in them slip rings...I think they were around £350 to replace
Thank you for such a thorough tear-down. The dynamic tracking heads are the larger assemblies with the piezo transducers. If I understand right, the dynamic tracking heads are for playback only (if I'm wrong I want to know). The reason (again if I understand right) is that because DT heads aren't rigidly fixed in place they might move around during recording as they won't have a track to lock onto (having just been erased). The recording head moving would result in a recording that doesn't have properly curved tracks. Although dynamic tracking on playback might be able to track that, it would not playback well on say, a BVW 70 which only has fixed heads and cannot track uneven tracks.
I work on VTR's a lot and have been waiting to work with these things for 20 years and 'just' got 3 of them about 6 months ago and I'm working out how to restore full operation for actual editing. Two of them are in far worse shape then yours there and Betacam is more complex then anything I've worked with yet. so I'm getting useful info from your video that I haven't seen in the incomplete bits and pieces of manuals I have. Always good to see anyone working with these.
In Record mode the DTF heads are applied a fixed voltage relating to the centre of the desired track, to ensure compatability with non DTF machines. The DTF system was also used in the Philips / Grundig V2000 domestic machines. E.g. Vr2020 and 2x4 super. I have worked on these machines for many years and love the diverse engineering not only electronic but mechanical systems too.
The DT heads were playback only, they allowed slo mo and freeze frames. That is the difference between the BVW-70 and 75.
Guessing the DTF heads are offset pairs , so it adjusts the video head position based on the difference in signal level between them
+mikeselectricstuff I would think so yes, i did think about this while i was editing, that i should have checked the shim thickness between the two adjacent fixed DT read heads as i think there should be a small offset between them
Beautiful teardown (as much crying I was doing watching you cut this system up). But very nice to see the hidden aspect of design. Again, Sweeeet . Thanks
I'm seeking for a scanned BVW 75 repair manual vol. 2, with all pages included (15-4 etc.).
Thank you for this detailed video. I knew that helical scan systems are complex but I never realized how complex they can get. Questions:
1) Was this piezo tracking feature a necessity in Betacam, or a feature present only in high-end machines?
2) Do they have such tracking in VHS heads?
3) Do the later digital helical scan systems like DAT and MiniDV also use this, or did they eventually find a different tracking method that allows for simpler/cheaper head assembly?
It's hard to say, there are so many systems in so many markets. I would be surprised if any domestic VHS machines used it, but the professional versions might. I have never seen it mentioned on any of the smaller implementations of HS like DAT, this could be due to the width and speed of the tape. Certainly the dynamic tracking was used widely in betacam & digibeta. The Sony D-1 format also used dynamic tracking, i'd love to teardown one of those machines!
Thanks for the answer! I'd love to watch you do a teardown of one of those machines ;)
Piezo dynamic tracking heads are not needed to record or play back tape, they are for obtaining a clear playback signal at tape run speeds other than normal. This makes still images, slow and higher speed search (2 to 3x normal, possibly more) look very nearly as good as playback speed. Without dynamic tracking heads (AST) the noise bands between video frames would be visible and not correctable via electronic means, although many VTRs can hide the mess by replacing the noise with previous image information. I have seen one professional grade VHS machine that has dynamic tracking but this feature is rare in vhs. The best dynamic tracking I've seen is on 1" reel to reel, Ampex vpr-3, although I believe there were betacam SP decks made with 3x playback.
As far as I know, dat and miniDV and many other other (but not all) digital formats rely on a digital buffer to hold image and other information while the tape is not in playback speed but they are able to pick up some information like track data and enough video data to make part of the frame visible. A clean still image is made by storing the last frame played into digital memory before the tape is stopped, some analog machines have a digital frame buffer to do this as well.
Any chance you could sell me the torn down head? I've been reading talk of using the bearing to make a rather cheap turntable bearing. I'd just need the mechanics rather than any electronics.
+nathnullobject If you go to my about page you can access my email, send me a message and we'll see what we can sort out: th-cam.com/users/DextersLab2013about
excellent video, as always !
As themastertrevor comments; All the extremely tight tolerance engineering, technology, electronics and Betamax was said to be better than VHS; now where is it... Even the Tape surface and substrate had Physics breakthroughs... To achieve this.
P.S. Spot of dirt on the tape, may jump a bit on playback but keeps going, DVD/BluRays stop died ...
Руки вырвать за то что он сотворил с этим аппаратом !!!!!!!
❤
Jeez you were right about these things being junked by the hundreds, they're all over ebay!
Very nice :). Now the challenge is to put it back together :D.
+nickhill92 LOL, not much chance of that!
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Christ how they engineering that!?
+Thiago Coura Research and lots of experiments!
Damn , that drum assembly is worth more then my suv and built better too.
love the intros haha
+CreativeType :-) thanks, they seem to be following a theme...
The DTF system was also used in the PHILIPS V2000 VCR with the double sided video cassette, if these numb skulls don't stop butting in I am moving to Linus Media's FLOAT-PLANE.
1kg just in screws
feel bad for the sony betacam