Excellent description of back-tension and how it's achieved in various machines. At work we had a very expensive device called a Tentelometer for checking tape tension.
Used to use one of those, too. Bloody expensive! First engineering job was at Technicolor Videocassette - huge duplication plant, tens of thousands of JVC BR-7000 decks, which thankfully had "proper" reel motors with electronic back tension adjustment. Had all the proper gear, of course...MH-2(?) Test tapes, Tentelometer things, those other things with a little dial (forgot the name) for drum eccentricity adjustment, etc etc. I think the tool kit for the Sony 1" decks came with a Tentelometer too. Anyway...enough of my rambling down memory lane...😄
@@njm1971nyc Interesting. The company I worked at (in central London) also had a duplication facility with dozens of BR-7000's - I worked on many of them!
Another comment to add...on my SVO-5800 VHS decks I do sometimes go into the service menu and temporarily alter the back tension to get troublesome old tapes to play better. Can certainly come in handy being able to do it without disassembling the deck and messing around inside!
Funnily enough I had a DAT deck misbehaving just this past weekend. Played fine for a few seconds then suddenly speeded up. At first I suspected capstan servo issues, but in fact it was back tension trouble. The tape was riding down (completely)on the capstan and the high speed playback was just the take-up spool pulling the tape with zero input from the capstan/pinch. Thankfully it was a good quality DAT with electronic back tension control/ independent reel motors. Just a tiny tweak of the (helpfully-labelled)) pot was enough to fix the problem. Yay! 🙂
hello, just to add some precision on back tension on N1502/1700. the way you rotate the supply spool is actually the way it spin in rewind, so it has to spin freely as possible and totally normal. you really don't want excessive back tension in fast rewind. by trying to add back tension in rewind, you'll dramatically increase the desirable back tension (as you experienced it :)) what happen with the fricition system itself is the clutch under the spool tend to crack, because there's a metal frame in it... and cracks make the surface "bumpy" so the felt pad have less surface contact. so you need to lightly sand paper (800) the surface to get it flatter, then back tension come to normal. you probabely also see the 2 rubber brake under the clutch, they are crucial as in play direction they block the clutch and release it in rewind. they need to be there and in good shape, and it's not always the case, sadly. PS : did you get my last email about the cvbs amplifier pcb i sent few weeks ago ?
I think that "uncontrolled" back tension, either mechanically applied with friction pads or clutches or magnetically applied essentially amounts to the same thing: setting a constant torque on the supply reel (of course in the mechanical systems the reel needs to be rotating for this to be true). With the mechanical system, this torque can periodically vary along one rotation due to uneven friction surfaces and will be susceptible to wear. But the end result is similar, the back tension will be inversely proportional to the radius of the supply spool in both cases.
Yes i've had my fingers in to the back tension band on my old jvc piano beast years ago. Tracking will move slightly with tension. For a rough head guide set up, i wound the tv height down a bit so i could see the head switching at the bottom. Also i found the tracking changes as i watched or recorded videos. Another problem is squeeling or vibration of the tension band, one tiny drop of light oil on the band and it shut up for years. I didn't repair other peoples vcrs the same wayi did mine.
Many better open reel audio tape machines used servo backtension, either mechanical or electronic. A very few cassette decks such as the Tascam 122 MkIII used electronic servo back tension. Direct tension sensing is not really possible in an audio cassette so the Teac electronics inferred tape back tension from reel speed and made the correction via a magnetic clutch/brake in the supply table.
Thanks for mentioning the problem of excessive back tension with very small diameter open reel tapes. It can be exacerbated as customers often bought the very thin based , easily damaged tapes to make longer recordings. Often a safer machine to play these fragile reels is one like a Uher Report which in later models used mechanical servo back tension.
Another advantage of servo back tension in both audio and video machines is longer head life. Back tension can be set to be just high enough for reliable tape to head contact but no more, resulting in lowest wear. Whereas with no back tension regulation, BT must be set for adequate tension at the start of the reel where tension is lowest. From then on through the reel, back tension increases as does head wear rate.
hi you can change the back tenson on pro reel to reel sony tc755 is down the side of the decks good point in the video decks the home decks i have not had alot of hrs on fixing them you are right about the motor in the pro decks some times the card that deal with the motors goes bad just change over card alot of the time and recap it
Inside the JVC VCR you demonstrated, I've always assumed the flywheel on the left side of the video drum that sits on top of one of the idlers acts as a speed ripple dampner, Is it what I think it is?
Hello. I want to ask a question not entirely related to this topic, but I watch your RUclips channel and I know that by recording analog video you can have knowledge. I'm interested in your experiences in converting between TV systems... especially different versions of NTSC to PAL. Can you recommend any devices or method for this purpose?. I would like to privately convert video material from several NTSC Laserdiscs to PAL DVDs. My LD player is an old junk.. Maybe others would also be interested in this topic. Regards.
Some standards converters do a much better job than others for this. The best one I have is a G2 MSTC Ultima. But all of these units are hard to source now.
Thank you for your answer. Unfortunately, the model you provided is not available to me. But I have the option to buy a used Datavideo STC-100, or Kramer FC-4000, or a new digital 'Oerei' from India. I have no idea which one will be good for my laserdisc work. Which one do you think would be best for this purpose? Greetings from Poland.
Hi, now i watched your video, i remember our first video recorder, a Hitachi VT8000, it's a toploader but already with touch-button servo mechanism, we had it a long tme, until there was an anoying gong sound that it made, so we bought an otherone, could this gong sound be related to the back tension problem ? Looking through my collection of VHS tapes i only discovered two really bad VHS tapes Sonor, and a 3M Scotch tape, which have random white dropouts (no bars) so i guess the dropouts are from missing oxide particles ? could another VHS vcr do a better job in compensating/masking these drop outs, for better digitizing results ?
yes, drop-out compensation can be very different between VHS manufacturers. from my point of view, the only manufacturer who provided very good DOC, even on big ones, is philips. they had long experience in that from VCR to V2000, and their home made VHS circuitry took advantage of that.
What about personal stereos that had no supply reel motor, just a peg that stuck up where one should be. Did the compact cassette housing take care of the tape path and/or back tension reducing the need for it or were those mechanisms just bad?
hi this is a very good point i know a man he got slave decks there have to be binned because the back tenson of the reel motors are very bad emi btr4 slave i tryed to max out the back tenson the decks have done alot of hr they will rew ff but the on tenson on the tape when it's say ff the tape to the reel it's just speed with out tenson you got to have tenson in the ff rew yes the decks come to the end of there life now 1957 about the decks are
Excellent description of back-tension and how it's achieved in various machines. At work we had a very expensive device called a Tentelometer for checking tape tension.
I used to use a tentelometer, but only on 3 motor drive machines.
Used to use one of those, too. Bloody expensive! First engineering job was at Technicolor Videocassette - huge duplication plant, tens of thousands of JVC BR-7000 decks, which thankfully had "proper" reel motors with electronic back tension adjustment. Had all the proper gear, of course...MH-2(?) Test tapes, Tentelometer things, those other things with a little dial (forgot the name) for drum eccentricity adjustment, etc etc. I think the tool kit for the Sony 1" decks came with a Tentelometer too. Anyway...enough of my rambling down memory lane...😄
@@njm1971nyc Interesting. The company I worked at (in central London) also had a duplication facility with dozens of BR-7000's - I worked on many of them!
Another comment to add...on my SVO-5800 VHS decks I do sometimes go into the service menu and temporarily alter the back tension to get troublesome old tapes to play better. Can certainly come in handy being able to do it without disassembling the deck and messing around inside!
Funnily enough I had a DAT deck misbehaving just this past weekend. Played fine for a few seconds then suddenly speeded up. At first I suspected capstan servo issues, but in fact it was back tension trouble. The tape was riding down (completely)on the capstan and the high speed playback was just the take-up spool pulling the tape with zero input from the capstan/pinch. Thankfully it was a good quality DAT with electronic back tension control/ independent reel motors. Just a tiny tweak of the (helpfully-labelled)) pot was enough to fix the problem. Yay! 🙂
New subscriber - i love of all sorts of physical media and i find these videos fascinating, thanks for sharing your knowledge 👍👍
hello,
just to add some precision on back tension on N1502/1700.
the way you rotate the supply spool is actually the way it spin in rewind, so it has to spin freely as possible and totally normal.
you really don't want excessive back tension in fast rewind. by trying to add back tension in rewind, you'll dramatically increase the desirable back tension (as you experienced it :))
what happen with the fricition system itself is the clutch under the spool tend to crack, because there's a metal frame in it...
and cracks make the surface "bumpy" so the felt pad have less surface contact.
so you need to lightly sand paper (800) the surface to get it flatter, then back tension come to normal.
you probabely also see the 2 rubber brake under the clutch, they are crucial as in play direction they block the clutch and release it in rewind.
they need to be there and in good shape, and it's not always the case, sadly.
PS : did you get my last email about the cvbs amplifier pcb i sent few weeks ago ?
I think that "uncontrolled" back tension, either mechanically applied with friction pads or clutches or magnetically applied essentially amounts to the same thing: setting a constant torque on the supply reel (of course in the mechanical systems the reel needs to be rotating for this to be true). With the mechanical system, this torque can periodically vary along one rotation due to uneven friction surfaces and will be susceptible to wear. But the end result is similar, the back tension will be inversely proportional to the radius of the supply spool in both cases.
Great camera work on the N1502 while taking the reels off. :) (and a great repair)
Yes i've had my fingers in to the back tension band on my old jvc piano beast years ago.
Tracking will move slightly with tension.
For a rough head guide set up, i wound the tv height down a bit so i could see the head switching at the bottom.
Also i found the tracking changes as i watched or recorded videos.
Another problem is squeeling or vibration of the tension band, one tiny drop of light oil on the band and it shut up for years.
I didn't repair other peoples vcrs the same wayi did mine.
Totally agree, for some reason the auto back tension on the Panasonics NV HS1000 is gone so dry that it can’t even play.
Many better open reel audio tape machines used servo backtension, either mechanical or electronic. A very few cassette decks such as the Tascam 122 MkIII used electronic servo back tension. Direct tension sensing is not really possible in an audio cassette so the Teac electronics inferred tape back tension from reel speed and made the correction via a magnetic clutch/brake in the supply table.
Thanks for mentioning the problem of excessive back tension with very small diameter open reel tapes. It can be exacerbated as customers often bought the very thin based , easily damaged tapes to make longer recordings. Often a safer machine to play these fragile reels is one like a Uher Report which in later models used mechanical servo back tension.
5:40 "ackshuallee" the amount of back tension would depend on the current through the motor (not the voltage).
Another advantage of servo back tension in both audio and video machines is longer head life. Back tension can be set to be just high enough for reliable tape to head contact but no more, resulting in lowest wear. Whereas with no back tension regulation, BT must be set for adequate tension at the start of the reel where tension is lowest. From then on through the reel, back tension increases as does head wear rate.
hi you can change the back tenson on pro reel to reel sony tc755 is down the side of the decks good point in the video decks
the home decks i have not had alot of hrs on fixing them you are right about the motor in the pro decks some times the card
that deal with the motors goes bad just change over card alot of the time
and recap it
Did Michael inspire you ? That lovely old NV-333 :)
I found the Nv333 to be a good old beast that performed well, even when old.
Inside the JVC VCR you demonstrated, I've always assumed the flywheel on the left side of the video drum that sits on top of one of the idlers acts as a speed ripple dampner, Is it what I think it is?
Something like that, yes. These appear on various VHS decks but certainly not all, so it's possibly not a vital component.
Hello. I want to ask a question not entirely related to this topic, but I watch your RUclips channel and I know that by recording analog video you can have knowledge. I'm interested in your experiences in converting between TV systems... especially different versions of NTSC to PAL. Can you recommend any devices or method for this purpose?. I would like to privately convert video material from several NTSC Laserdiscs to PAL DVDs. My LD player is an old junk.. Maybe others would also be interested in this topic. Regards.
Some standards converters do a much better job than others for this. The best one I have is a G2 MSTC Ultima. But all of these units are hard to source now.
Thank you for your answer. Unfortunately, the model you provided is not available to me. But I have the option to buy a used Datavideo STC-100, or Kramer FC-4000, or a new digital 'Oerei' from India. I have no idea which one will be good for my laserdisc work. Which one do you think would be best for this purpose? Greetings from Poland.
Hi, now i watched your video, i remember our first video recorder, a Hitachi VT8000, it's a toploader but already with touch-button servo mechanism, we had it a long tme, until there was an anoying gong sound that it made, so we bought an otherone, could this gong sound be related to the back tension problem ?
Looking through my collection of VHS tapes i only discovered two really bad VHS tapes Sonor, and a 3M Scotch tape, which have random white dropouts (no bars) so i guess the dropouts are from missing oxide particles ? could another VHS vcr do a better job in compensating/masking these drop outs, for better digitizing results ?
yes, drop-out compensation can be very different between VHS manufacturers.
from my point of view, the only manufacturer who provided very good DOC, even on big ones, is philips.
they had long experience in that from VCR to V2000, and their home made VHS circuitry took advantage of that.
@@whaka54000 There are also Philips VCR's that are rebranded ones i'm affraid...
What about personal stereos that had no supply reel motor, just a peg that stuck up where one should be. Did the compact cassette housing take care of the tape path and/or back tension reducing the need for it or were those mechanisms just bad?
Back tension may be less critical due to the felt pad in the cassette but it's clearly not ideal.
two channels i watch releasing a video mentioning back tension on the same day, lottery ticket odds...
(StvB8i5dqUE)
hi this is a very good point i know a man he got slave decks there have to be binned because the back tenson of the reel motors are very bad emi btr4
slave i tryed to max out the back tenson the decks have done alot of hr they will rew ff but the on tenson on the tape when it's say ff the tape
to the reel it's just speed with out tenson you got to have tenson in the ff rew
yes the decks come to the end of there life now 1957 about the decks are
*sigh* I have to say it. "SHWING! SCHING!" No I'm not proud of myself.