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Beginners Guide to Tape Recorder Basics

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ironbut:
Hey Steve, thanks for those corrections/additions. In the 1/2 track post I was trying to show a Studer 807 picture with the Sony but I guess it was too big a file. It was set up for having the "extra" playback head last just like you said (Duh!).
As I said before, I encourage any and all to post info that I've omitted  or gotten just plain wrong (I'm pretty much doing this off the top of my head). This thread is, after all, to educate and not to mislead (like my other posts). Before I move on to a totally different subject, I'll wait a week so we can keep these in the same general area.

ironbut:

By ironbut at 2008-09-01

Ok,.. just a little head basics. I won't go into lots of technical stuff since this is a beginners guide. Heads are (see top illistration) made of laminations of alloys in 2 main parts. If you look at the bottom cross section, there's a right and left half. To orient you, the tape would be traveling left to right or right to left across the top of the bottom picture. You can see that the haves are made up of "C" cores just like some transformers. Between these cores is a small space called the gap (of all things). The gap is the muzzle of the head. It's where the magnetic flux is allowed to flow out of the head and magnetize the tape. There's a spacer placed into the gap and the whole thing is epoxied into a single piece. One thing to keep in mind with these transducers is the extreme tolerances that they are machine and polished to (we're talking micro inches here). And just like lot's of things here on the planet earth, the material that heads are made of are a balancing act of compromises. In this case, it's between permeability and hardness (output and wear characteristics).
You might ask about the "glass" heads that Sony and Akai used in many of their latter models. I owned a couple of those and the problem with those heads is that they don't wear like a metal head which is usually pretty regular and smooth. They develop microscopic shearing of the crystals that surround the gap. After a while these develop into micro-chips (Hey,.. don't go there CV!) and can do real damage to your valuable tapes without you ever knowing it. Once they go bad, they have to be replaced.
With metal heads after they get worn, they can still be resurfaced (lapped). If you look at the first illustration there's a area on the top labeled "Depth of Gap". When a head wears, a flat spot begins to appear where the tape makes contact. An extreme case of this can be seen in the photo on the right. A head can be relapped until the "depth of gap" begins to equal zero. Since the gap spacer is just that, a spacer, when the gap begins to open up like the track on the bottom of the photo. That head is history.
When the wear isn't nearly as extreme as it is in the photo, the head can be reshaped and polished. How fast a head wears depends on several things.
The hardness of the metal the head is made of.
The speed that the machine is used (30 inch per second machines will wear out heads much faster than 7.5 ips machines)
The abrasiveness of the tape that's used.
The tape tension the machine is set at.
The cleanliness of the tape path and tapes.
Proper adjustment of the heads and guides.
Temperature and humidity (heads will rust ).
Most machines you'll come across aren't going to be as obviously worn at the picture above and to get a good idea of the wear you should use a magnifier of some sort and a good light. Look for the shinny flat spot (which all will have to some degree) and the real tell tail clue is grooving. This is something that you can feel. A head that needs relapping will have a ridge that you can feel with your fingernail (be very gentile, remember some of these heads are made of soft metals and you don't want any scratches on them). Even if you feel this ridge, it doesn't mean that the heads that worn either. Many heads have what's called "edge relief slots" cut into the surface right where these ridges would normally be found. They're there to keep the tape edge from being damaged by a ridge and also to prevent shedding oxide from being trapped along these ridges and escalating the tape and head wear. So, unless you get a good look at the head, you may just be feeling these slots. Also, it's important to see if the wear is even or not. That will tell you more about the condition and adjustment the heads and tape path were in during the majority of service. These are all great clues on how well the machine was cared for or if it was taken to a total hack for regular servicing. If you already own the machine, examining the head wear pattern will tell you if you need to take it in for adjustment. Worn heads can result in high frequency loss, excessive tape wear, inconsistent output (dropouts) and loss of overall output. As you can see from the open gap on the bottom of the head in the photo that this machine either needed to have the heads or guides adjusted. If the uneven wear (from top to bottom) was the result of the head being tilted back, the adjustment that would correct this (here it comes!) is called Zenith.
Just a few more things about heads for this post.
If you should need or choose to replace your playback head/s here's the main things you need to know when you choose one. The two spec's usually associated with them is DCR and fluxivity measured in nano Webers per meter (nWb-m). A service manual will have these figures. The fluxivity is a reference number when you wish to choose an alignment tape too. 185 to over 500 nWb-m heads can be found. Aside from those two figures, many times space available will be another determining factor for which heads can be used with a particular machine. Remember that with playback heads they almost always have a shield around them so the fit can be tight.

If you're interested in more info regarding relapping and head wear, John French is the man and his web site is full of info.http://jrfmagnetics.com/

Here's JFR's procedure when relapping heads:

In the JRF alignment procedure each head (erase, record and playback) is
aligned for track placement (referenced to the tape guides and set within
.0005), zenith (90 degree tilt), wrap (gap centered on tape contact scrub
pattern), and azimuth (90 degrees).  Head assemblies that do not have tape
guides attached to the head plate are mounted on our lab fixtures that
simulate the recorder tape path (with guides for height reference).

Upon re-installation of our optically aligned assembly we recommend the
use of a test tape to optimize the azimuth for phase.  This is required
because of the tolerance differences between tape width (typically .246)
and guide width clearance (.252).  As you can see, there is about .006
clearance which can allow the tape to enter the assembly incoming guide
low (or high) and exit the outgoing guide high (or low).  This potential
tape path error along with the quality of the tape slitting
and/or other components in the tape path (such as the pinch roller) will
have an effect in the azimuth that cannot be anticipated in the lab.  We
are generally dead on about 70% of the time however, I always recommend
the use of a test tape.

ironbut:
OK, that's enough on heads exclusively. To begin with recording tape, I'm going to send you to the National Media Library for a bit. This is a document that's directed to libraries and other facilities that may be dealing with recording tape in their collection. It includes sections on open reel analog, video, and digital tape. You can pass over the sections dealing with other formats of magnetic tape, but you may also find some interesting things contained in these sections which will broaden your understanding.
Those of us who are old enough will remember the days of large mainframe computers (being here in Silicon Valley I have lots of friends who worked with these at IBM and Control Data Corp). Some of the last major R&D that went into tape transports came from improvements in these data banks.
Bear in mind while reading through this document that some figures given are for a worst case (tape lasting only 10 years for example) and we will later outline what would constitute such a worst case.
There is a glossary and a tape care guide from Ampex but here again, there are items which aren't very relevant to our use (such at reel collars, which were the plastic "bands" that went around the circumference of a reel that kept dust from entering, mostly for computers).
Please pay close attention to discussions of sticky tapes since getting your head around the "stick>slip" mechanism is important. This will be a recurring theme in latter discussions (it's really an extreme cast of very uneven friction).
So here you go,.. "Take it away Dr. Bogart!)
http://www.clir.org/pubs/reports/pub54/1introduction.html

ironbut:

By ironbut at 2008-09-13
Once again, I start this episode with some pretty pictures. Nothing is too good for my special friends here at the Tape Project.
The first two are pictures of the different way that light shines through acetate and polyester tape. Holding the reel up to a light will show that the acetate lets light through. This was important since acetate was the backing that was used for films in the early days. This is the easiest way to determine what you've got. The most important reason for identifying an acetate tape is that, as opposed to polyester backed tape, acetate will not stretch. The older the acetate tape is, the more brittle it will become. For that reason, very careful handling needs to be taken to avoid breaks. Some of the things that you should do is to attach long lengths of leader ( I now splice in 2 full turns of white leader tape and 5 full turns of RMGI recording tape that I have around, just like the Tape Project tapes are done). The reason for this is that there is "no" reason that I ever have to subject the acetate to starts and stops or handling at all. The other thing to avoid is rewinding or fast forwarding these tapes. Of course this can be time consuming with 1/2 track stereo tapes but like I said,.. avoid it if you can.
This brings us to an often mentioned term of "gentile tape handling" or tape handling by a machine in general. This encompasses just about every adjustment on a machine and really starts in the design of the tape transport. For now, I'll just mention the basic adjustments that are directly related to the preservation of your tapes.
Brakes- The brakes should slow the two reel as a team rather than fighting each other. If you turn the reels on your machine with it turned off (and the brakes engaged) you'll notice that the turntables have more resistance in one direction than the other. In fact, you'll find that the side that would be pulling the tape (take up reel) always has more braking applied than the side that would be supplying the tape (supply reel) no matter which direction the tape would be traveling in. You can imagine that if the opposite were true than breakage or stretching would occur. So, having the brake tension and the timing of the braking just right is important.
Tape Tension- On most machines, it's the motion of the capstan that controls the flow of tape during play (I'll get more into the what and whys of capstans latter). The reel motors pull the tape in opposite directions applying tension to the tape. You can see this for yourself if you turn your machine on play without a tape threaded on it. The tension helps keep the tape flowing smoothly through the guides and creating an even tape pack as it goes. Correct adjustment of tape tension is important to prevent slippage as the tape is metered through the capstan/roller assembly.
If you look at the third photo of "uneven wind" you will see one of the main causes of problem tapes. Tape pack is how evenly the tape appears from the side and indicates how each layer of tape is laid upon the layer underneath it. Anything that the tape comes in contact with on it's way from the supply reel to the take up reel effects tape pack. That includes air. In fact, one of the main causes of an uneven wind is air. On the sides of a tape reel there are holes of one sort or another. On the Tape Project reels we have cool looking circle/square/triangles. On plastic reels, they're more like the holes that form spokes but it's the holes that are important. These are called windage holes and for good reason. As the tape winds onto the layer beneath it, there is air pressure created between them. Of course there is much less pressure the slower the tape is laying down but the faster this happens, the more likely that the air pressure will begin to act against the tape tension. The windage holes help to release some of this pressure. But this is one of the reasons that a tape has a less even wind in fast forward or rewind.
So what's so important about getting an even wind?  The tension that's applied to the tape as it travels through the machine doesn't go away once the tape is on the reel and put away . It's still there pulling each layer of tape toward the center of the reel. If the tape is stored like the third picture, the edges that are unsupported are allowed to move farther toward the center then the rest of the tape. Even a relatively short time of storage in an uneven wind will give this curling a memory which may not show up except on playback. If you laid a strip of a "curled" tape on a flat surface you'd see that it won't lay flat. The oxide side is lifted off the surface by the curling and the same thing happens when it tries to lie flat against the head. This results in a loss of signal on that channel. And after the discussion of heads told you, if it's a 1/4 track tape, your left channel will be lower in volume or at least, have some high frequency losses.
Other problems associated with an uneven wind is that when a tape is correctly wound, the oxide is protected by the other layers of tape on top of it. When the tape is sticking out on an uneven wind, the oxide on those layers are exposed to dust and impurities in the air.
A correctly wound tape will appear flat and a little shinny through the windage holes. The best way to ensure that this happens and avoid "curling" is to store your tapes in a played condition rather than fast forward or rewind. If you look at the polyester example, it looks pretty good except for a couple of spots that appear as a dark lines. These were probably caused by stopping and restarting the tape at those points. A correctly adjusted machine will minimize these and except for very long storage, I wouldn't worry too much about this.
Probably the most common problem with any tape is called drop outs. These appear as momentary drops of the volume on playback. The most common reason for this is dust or some other contaminant on the oxide surface which interrupts the tape/head contact. This can happen to even the best cared for tape and the narrower the track (1/4 track) the more obvious and distracting it will be. Luckily many times these contaminants can be removed. If you collect a lot of eBay tapes, you should keep a roll of Pelon cleaning tissue around. This can be obtained from US Recording Media and depending on your tape path, it can be held on the tape at any easily accessible spot and will gently clean the oxide side of your tape as it's moving. Since it's usually 7" reels that I have to clean, I use it just after the tape comes off of the supply reel. I use an old aluminum film container that I epoxied a thin suction cup on the bottom (which I kinda smooshed in) so when I stick it to the surface of my deck, it's almost flush. Then I tape some Pelon on it and play it at 15ips. I rotate the can a couple of times to keep clean Pelon on the oxide. (edit: I usually just use my finger on rewind now)
Just one other thing to mention regarding acetate tape in particular, never bake it! You shouldn't have problems with sticky shed (as mentioned by Dr. Bogart) with this type of tape but if you do, baking will ruin acetate so another solution will need to be taken.
Well, I think that's enough for this post. Next time I'll talk a little about other common problems.
http://usrecordingmedia-store.stores.yahoo.net/quclwi1x15.html

ironbut:
Sorry, no pretty pictures to start this one out. There are a number of problems you'll encounter along the road especially if you've decided to collect older tapes from auction sites or elsewhere. One that you'll come across even if your tape collection is still small is called print through.
Print through isn't something that's damaging to the tape itself but rather, it's distracting and interferes with your enjoyment of the music. It manifests itself as a pre or post echo on playback. This is similar to crosstalk that we discussed earlier in our discussion of heads and height adjustment. It's easy to tell the difference between the two since the sound of crosstalk is usually backwards while print though is not (this is on 1/4 track stereo). The sound recorded on the tape is printed on the tape by magnetizing the oxide particles. If a tape is left unplayed for very long periods, these oxide particles will begin to influence the oxide on the tape adjacent to it. A good analogy to this is the way that the early plasma screen TV's, if left with the same picture on it for 10's of hours, would be left with a ghostly image of that picture forever.  Luckily, most print through isn't heard because the music intentionally printed on the tape usually completely obscures it. It's particularly distracting during quiet passages of music when loud sections have been superimposed upon it. There's no known cure for it but there are things that can be done to help to prevent it.
The main thing to do is play your tapes. Even if you had the mythical perfect tape transport, since most tape will stretch, the odds that your tape would be wound exactly the same way twice is pretty much impossible. So do yourself a favor (in more ways than one) and listen to all your Tape Project tapes at least a few times a decade. That may sound funny but there may be some of the releases that just don't float your boat and in a decade, we'll have 100! Woo Hoo, won't that be cool! But of more immediate concern are old tapes you might buy. If you've collected for very long, I'm sure you've bought a few "dogs" with erased sections, bad splices and tons of dropouts. That will lead you to jump at tapes advertised as "still sealed" or "never played" and bid your kids college fund on them. Well, everyone has a personal tolerance level for different audio distortions and I have to admit that mine is pretty high for print through, but if your looking for tapes that don't have it, these unplayed tapes aren't for you. They're more likely to have audible print through than ones that have been played from time to time. You can reduce the level of this print through by repeated playing or rewinding. Some say that it can be reduced by over 2 dB but like I said, if the music is great, I can overlook it.
Stretching The main reason for tape stretching is poor machine adjustment. When you push the play button on a tape deck, several things happen.
1. The brakes release
2. The reel motors engage
3. The pinch roller/s push the tape to contact the capstan
The exact timing and order of these elements will vary from machine to machine but one thing is constant,.. improper adjustment of these will cause tape stretch. In actual fact, proper adjustment will cause tape stretch too but not enough to damage the tape. The thinner the tape backing, the more the tape will stretch so I usually try and avoid buying tapes that have multiple albums on them since that's how they fit them on one reel.
A stretched tape can't be fixed and the "wow" sound that is evidence of this problem is usually accompanied by dropouts since the oxide usually sheds because of the increased length.
Broken tape or bad splices If you buy really old tapes such as the acetate tapes discussed in the previous post, you'll eventually have to deal with a broken tape or fix splices from the previous owner/s which were made to either fix breaks or change song order or some other editing.


By ironbut at 2008-09-17
This is a splicing block. To fix breaks, splices or add leader to the beginning or end of a tape you need one of these. As with most of the tools that I'll mention, US Recording Media sells them. You'll also need some splicing tape, single edged razor blades and a roll of leader. I was never taught how to use one of these but the basic use is pretty straightforward and the more you use one, the easier and better the result will be. As you can see, there are two slots that cross the length of the block. The slot on the left (diagonal) is for editing and the one closer to the middle is for general purpose. There's also a channel that runs the length and is made to fit the size tape that you purchased the block for (there are 1/4" to 2" blocks). I'll use the addition of leader as a example.
Place the reel of tape on the left of the block. Place the end of the tape that you want to add leader to in the channel oxide down (no matter why you're using the splicing block, always place the tape oxide down)with around an inch past the middle slot. Press the tape securely into the channel.
Place the reel of leader(or a pre cut length) to the right of the block and place the leader into the channel with and inch past the slot. Press the leader into the channel on top of the tape. Use the razor blade and insert into the slot above the tape/leader and slice it down (think paper cutter) cutting both. Use the corner of the blade as a pick and slide the leader end out of the way without moving the tape or the rest of the leader. Take 3/4" of splicing tape and line it up with the channel (this is the part that takes some practice) by looking straight down at the tape-leader joint. Apply a little pressure to the splicing tape and remove the spliced tape/leader from the block. Put the joint on a hard surface and if you're happy with the splice, apply more pressure to the splicing tape. If there's not splicing tape overlapping the tape/leader and is perfectly straight, congratulations! Measure off the amount of leader you want (I usually add at least 3 full turns) and snip it with a pair of scissors.
If you're fixing a break or a bad (old) splice I use the same slot. The angled one is to make a smoother transition and you can try that one too but the tempo gets interrupted either way but you may prefer the angle. Other than that, there isn't that much difference just remember that the splicing tape is always applied to the back and not the oxide side of the tape.
Mold or mildew This usually appears as a dusty white coating visible on the sides of the tape. For the most part, unless the tape is fairly valuable, it's best to discard it since the spores will contaminate your other tapes via your machine as you play them. The mold is a health hazard to boot.
Just a word or two on the term tails out. With 1/2 track stereo tapes (like the Tape Project tapes) which are unidirectional, it is considered best practice to store the in a tails out configuration. This means that the tape must be rewound to listen to it. To do this you place an empty tape on the left reel platter and the full tape on the right. Thread the tape as the machine is normally done and rewind it fully. Now the tape is heads out and the full tape is on the left side (supply side). Now it will play correctly. One thing to keep in mind with 1/2 track stereo tapes is that no matter how you manipulate the reels, flipping it or moving it from side to side, rewind, play or fast forward, as long as you thread the tape the correct way, it will only play either correctly or in reverse. Nothing you can do will move the left channel to the right. That said, if you wish to change a heads out tape to a tails out one and you don't care what reel it's on, all you have to do is put the heads out tape on the left reel platter and put the reel you're going to keep it on, on the right. Play tape and now it's tails out. If you want to keep it on the original reel, you'll need a second empty reel and put it in place of the now empty original reel and rewind the tape onto that one. Now replace the empty reel on the right with the original reel and play the tape onto the original.
Next
Tape care tips.

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