how many times can you record on the same tape?

[amnesia]

just wondering, to save costs I am going to copy my recordings to tape to give them that tape sound, but as we all know 1/4" tape is expensive, so how many times can i record on the same tape before i will hear loss of quality? or can i buy a new tape record once on it and demagnetize it and start again?
new to tapes

[ironbut]

Unfortunately, that's a kind of complex question. There's a number of variables involved but the simple answer is that theoretically, the oxide shouldn't wear out in it's ability to flip it's magnetic charge. The barriers that prevent this "flipping" are determined by the charge of the molecules so this shouldn't change either. These barriers maintain the orientation of the charges so it prevents the magnetic imprint from changing (although these potentials can be changed by temp.).

What makes this a complex question in the real world are differences in the tape and the machines ability to fully erase the previous imprint. Using a bulk eraser makes this less of an issue since they're usually much higher powered than our little erase heads.
I used to do some work at a radio station when dinosaurs ruled the earth and we used to use bulk erasers on the cartridges that we used for ads and other prerecorded spots. We used those carts over and over again and they did wear out and sound terrible after a while (that's not to say we stopped using them though!). I believe this was more to do with the awful state of the cart machines (nobody ever cleaned those things until they absolutely had to).
So it really depends on the tapes ability to be erased correctly (which might be counter to it's ultimate sound quality) and how completely you can erase what was previously imprinted on it. Considering the few choices we have in tape formulas, I'd suggest using a tape that you like the sound of and finding a bulk eraser on eBay for cheap.

Maybe one of the other members here can chime in on a good bulk eraser to look for since all I can remember about the one I used was it was red!

To increase the life of any tape, good machine maintenance is key. Check out the Beginners Guide on tips about cleaning. It can be found above the General forum in one of the Stickies.

[Brian]

I used to work in a reel-to-reel duplicating facility "loaning" radio programs to subscribing stations (boy, I just dated myself!).  We would reuse our 7" reels 25 times - not because of the oxide "wearing out" but because of physical damage to tape edges by the equipment our member stations "sort of" maintained.

Each tape was degaussed on its return using a unit similar to this one, currently on eBay (I've seen similar ones by Magnetech or Ampex going for $10 - $200)

http://cgi.ebay.com/Comprehensive-Video-Supply-CVC-2500-Tape-Degausser-NR_W0QQitemZ200375864410QQcmdZViewItemQQptZVintage_Electronics_R2?hash=item2ea7550c5a&_trksid=p3286.c0.m14

If the unit "buzzes" when turned on, the only thing you have to worry about is whether both of the coils in the unit are working or just one - drop a penny onto each corner of the unit and look for equal vibrating. 

You should probably have a variac or similar variable transformer to fade up and down the degausser - it is the slow removal of the magnetic field that actually does the erasing.  Technique is:

1.  Turn on degausser with variac at zero.
2.  Put reel onto the spindle in the center of the degausser.
3.  Start spinning reel on the spindle (about 33 rpm should do)
4.  Slowly fade up variac to full power - over about 2 seconds.
5.  Hold degausser at full power for a second or two.
6.  Slowly fade down variac to zero - in about 4-5 seconds.
7.  Remove tape reel.
8.  Repeat with next reel.
9.  Do this for 8 hours while reading Playboy magazine and you'll experience my first real job.

Variac's are also available on eBay for $10 - $100.  Make sure voltage and max. current match those of the degausser (the inexpensive 10 amp variac should work for the kind of degausser in the link above). If you can't afford a variac right now, an alternate technique it to leave the tape off the degausser while you turn it on, slowly move the reel into the magnetic field, spin the reel, and slowly remove the tape from the surface of the degausser.  Ideally, you keep spinning the tape in your hand while moving it into and out of the magnetic field.  Start and end this process with the reel 2-3 feet from the degausser. 

This awkward process has been improved on in later models of degaussers that mount the coils under a conveyor belt.  Turn the unit on, put a reel on one end of the conveyor and, when it comes off the other end of the belt it has been slowly moved through the magnetic field and erased.  These units (by Gartner and others) can also be found on eBay for $500+ or new for $2000+.  I suggest waiting for a $10 Ampex or Magnatech unit and a $10 variac.

Hope this helps.
Brian

P.S.  After my first week of nonstop degaussing my supervisor informed me that I was now completely sterile and could have sex without any worries - fortunately I didn't have a girl friend at the time on which to test his theories (the supervisor had 6 kids of his own so. even as a dumb teenager, I tended to be a bit skeptical of his prognosis).

[ironbut]

Great tales from the trenches there Brian. BTW, I think that if you'd mentioned your wages at that time you'd really be dating yourself! (IIRC My first job at a dairy paid $1.25/hr and I was stoked!)
Your post may be very timely too since there is a query regarding some prerecorded tapes that are B wind in the General forum which you may be able to shed some light upon.
http://www.tapeproject.com/smf/index.php/topic,1091.0.html

There was a thread on the Ampex list a while back that was started by a fellow who was trying to erase some tapes with a center track time code imprinted on them. I believe he'd tried some generic degaussers but wasn't able to get rid of the audible time code (he wasn't sure of the original track configuration). It was suggested that he procure an Ampex Model 111 (I believe that was it) which several posters agreed was particularly effective for tough jobs. They do seem to be a little expensive though (I've seen a couple in the $100 range) so I'm sure the original poster can do better price wise.

[ironbut]

Hey Brian, since you're an "expert" at using a bulk eraser, I'd like to run a little info that I'm thinking about posting in our "Beginners Guide" for future reference.
I went back and checked the Ampex list archives and found a post regarding the "eraser dance" as they put it. Any practical advice or criticism would be appreciated.
This post is pertaining to a common problem with improper use of a bulk eraser where audible thumps are left which effect the re-recording. The poster is Jay McKnight.

"I've never been sure exactly what causes the thumps: Is it the
residual magnetization from the erasing field itself, as you imply?
Or is it that the earth's field is a "dc" signal that is "biased" by
the erasing field? If this is the case, it would seem that there would
be an optimum orientation for the eraser coil, to minimize the thump.

Sunday, September 21, 2008, 12:46:04 AM, euclid wrote:

e> The most important thing, assuming that the eraser is powerful
e> enough and big enough to do a good job on your tape, is to move
e> SLOWLY. If you put a tape on the eraser, spin it quickly, and
e> remove it quickly or turn the eraser off before the tape is far
e> away from the eraser, you will get the thumps. If you move
e> painfully slowly you will probably not get the thumps. As you move
e> the tape out of the field, it gets magnetized in one direction and
e> then in the opposite direction as the polarity of the field
e> changes. The trick is to move the tape out of the field slowly so
e> that the magnetizing of the tape decreases slightly each time the
e> polarity of the field reverses. If you move slowly, the remaining
e> magnetization will be almost nil when you finish.

e> An eraser using a frequency higher than 60 Hz would allow you to move the tape faster."

Through the magic of our modern social networks, here's a video of someone erasing a 10.5" 1/2" reel of tape;

http://vids.myspace.com/index.cfm?fuseaction=vids.individual&VideoID=3629317

Like I said, I don't know much about the subject but want to place these in our Guide so anyone with something to change or footnotes that should be included, speak now,..

[Ki Choi]

Just picked up the bulk eraser Brian had pointed out above to try instead of the old Radio Shack handheld video tape eraser I had been using.  It was working well but I noticed one of the test tapes I had erased had very low frequecy rumble like sigals left on (but no music) the tape even with multiple erasing with the RS eraser.  The signal couldn't be heard through my Studer meter bridge monitor speaker's low frequency range but could be seen with the VU meter.  The odd signal can be heard when I rewind or FF with repro head engaged and periodic chirpping sound.  Strangely enough, if I were to record with no inputs using the deck's erase head, I get silence... For a while I thought my headblock was magnetized but the tape behaves the same on other machines.

I will try the Brian's process with the big bulk eraser when it gets here.  Good thing I got two kids out of the way and don't have to worry about the side effects of mega eraser...

Thanks,
Ki

[Brian]

This post is pertaining to a common problem with improper use of a bulk eraser where audible thumps are left which effect the re-recording. The poster is Jay McKnight.

"I've never been sure exactly what causes the thumps: Is it the
residual magnetization from the erasing field itself, as you imply?
Or is it that the earth's field is a "dc" signal that is "biased" by
the erasing field? If this is the case, it would seem that there would
be an optimum orientation for the eraser coil, to minimize the thump.

I've heard a couple of different explanations of "thumps" but all seem to agree with Jay that it is residual magnetism from the degaussing field itself - they just differ on the the cause.  One is it is because the tape was rotated too fast, another says it was rotated at an uneven velocity, another that one of the two coils in the degausser was blown, and yet another says the degausser was turned off before the tape was out of the field and what you are hearing is the transient pulse of the collapsing field.  My personal favorite is this last one - turning off the degausser too soon.  I am positive it is not uneven rotation, since this produces a "swishing" sound (sometimes mistaken for a problem with the recorder).  Too fast rotation usually only produces incomplete erasing. 

In my step-by-step I should have mentioned that this was our technique for the old Scotch red oxide, low signal level tape.  For modern tape that is really holding a hot signal you should rotate much slower - about 2 rpm and, after degaussing one "side", you should flip the tape over and repeat the process for the other "side - but reversing the direction of rotation.  With this technique it is possible to reduce noise even below that left by a good erase head with properly adjusted bias.  I once ran a test in my studio comparing noise levels from brand new unused stock and the same stock bulk erased prior to its first recording cycle.  The bulk degaussed virgin tape had noise about 4 db lower than that of the factory new tape. 

e> An eraser using a frequency higher than 60 Hz would allow you to move the tape faster."

Yes, absolutely.  Some of the Hollywood studios used to use 400 Hz aircraft power supplies to power their degaussers.  Since tape recorder bias is in the 150 KHz to 180 KHz range, there isn't any limit to how high you theoretically could go (avoiding "microwaving" your tape would probably be a good idea!)

Through the magic of our modern social networks, here's a video of someone erasing a 10.5" 1/2" reel of tape;

http://vids.myspace.com/index.cfm?fuseaction=vids.individual&VideoID=3629317

The degausser technique is OK but the degausser shown is designed for 7" reels maximum - not 10.5" and definitely not 10.5" of 1/2" tape.  Also, a degausser has two separate coils in it and is built so that, if you're spinning the tape on the spindle, the tape is always moving at a right angle to the flux fields.  If you're going to spin it without a variac, or use a single coil unit like the one shown, or manually move the tape into the field - you should find out how the degaussers coils are situated inside the case so you can move the tape into and out of the fields at a right angle to their flux lines. 

And again, I definitely recommend spending the $10-$20 extra for a variac (also known as a powerstat or autotransformer).

Hope some of this helps. 
Brian

[Ki Choi]

I have seen an instruction on demagnitizing tape path in Sony APR service training manual that showed sprial motion of the demagnitizer approaching the tape guides and heads but never touching (1/16" limit) - after turning it on from about 3' away.  Does it make sense to do the same for each individual part or make the initial approach while sprialing but move horizontally once you get to the tape path and sprialing away when done...?

Ki

[Brian]

Hi Ki

Probably the expert on tape head/guide degaussing was R.B. Annis who's company still makes their excellent "Handi-Mag".  His instructions say you can "wiggle" the Handi-mag a bit when it is at its closest to the head or guide (but not touching it) but that the wiggle is optional - it is the slow removal of the magnetic field that does all the degaussing.  This is done to each part in the tape path individually (since, as you correctly point out, you want to move the degausser about 3' away from the head/guide - it would be impossible to do the entire tape path in one continuous degaussing operation). You don't have to turn the Handi-mag off and on between each head/guide, just move it at least 3' up and away from the head/guide and then slowly move it back into proximity with the next metal item in the tape path.  Don't forget to also do capstans and their idler wheels and the dash pots.  Sony's spiral motion would also be optional - but could be harmful if it it ended up increasing the speed of the degausser moving away from the head/guide.  If you want to satisfy yourself empirically that each item is magnetically neutral, Annis also markets a magnetometer for that purpose. It is included in the Handi-Kits or can be purchased separately.  The Handi-mag by itself goes for for around $75 and the kit with the magnetometer and accessories goes for around $150.  I have seen them on eBay - but always closing for about the same price.  I wouldn't by a used magnetometer - too delicate.  Here's a link to the Annis site:

http://www.rbannis.com/products/handmags.html

Brian