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MAGNETIC TAPES




REELS

Reels are wound on plastic or aluminium flange which diameter ranges from 3.1/4 to 10.1/2” for different playing time. Table below shows recording time referred to different speeds for standard and long, or extended, play tapes (one side only). You can use the table to covert the units of measure between the metric system and the Anglo-Saxon system and vice versa too.

RECORDING TIME TABLE    in hours:minutes
by www.soundfan.it

Reel size Tape
thickness
Backing
thickness
Tape length SPEED: inches per second
(cm) (inch)  (m)  (mils)  (ml)  (ft) 1.7/8 3.3/4 7.1/2 15
8 3.1/4 35 1.0 120 400 :45 :22 :11 n/a
12 5 55 1.5 180 600 :60 :32 :16 n/a
12 5 35 1.0 275 900 1:36 :48 :24 :12
18 7 55 1.5 360 1200 2:08 1:04 :32 :16
18 7 35 1.0 550 1800 3:12 1:36 :48 :24
26,5 10.1/2 55 1.5 760 2500 4:25 2:12 1:06 :33
26,5 10.1/2 35 1.0 1100 3600 6:24 3:12 1:36 :48

Double (and triple too) play tapes with reduced thickness were available at the same reel diameter. They were more fragile and deformable than standard and long playing tapes and were not used in professional field.


From the left: 3.1/4" (3M) - 5"(BASF) - 7"(SCOTCH) - 10.1/2" (REVOX) CINE - 10.1/2" (AMPEX) NAB

There are three different types of reel supports and locking systems:
  • the standard domestic CINE from 3.1/4" up to 10.1/2" reels;
  • NAB one for 10.1/2" reels for domestic and professional use. Reel to reel recorders always have the reel support plates with a three splines shaft with rotating upper part to lock both Cine reel or Nab adapter;
  • In AEG DIN support, available for studio and professional use only, tape is wound without a flange on a self support metallic core (the so called “bobby”) and locked on an open plate ("pancake") not compatible with Cine or Nab locking system (but easily interchangeable with them changing the upper part of the recorder reel supports in few minutes).
From the left: standard reel plate with CINE locking system - Nab adapter - Nab with aluminium hub - AEG DIN

Is interesting to know German sound engineers, to reduce the print trough effect and have the recorded tape ready to play, wound the tape on the metallic core with the magnetic coated side facing the outside not the inside as international standard.
This is why the Telefunken Magnetophon M series are available in two different versions one for the international market (“A wind” version) and another one for Deutsch market (“B wind” version) with the head block turned down or up
respectively
.


Professional studio recorders can use larger (14") pancake plates for very high speed (30 ips) recording or longer recording time at standard speed. (see photo below).


On the left: a 10.1/2" pancake plate fitting standard CINE locking system for domestic and semi professional recorders (as Revox, Teac, etc)
On the right: a 14" professional pancake plate with AEG DIN locking system for studio professional recorder (as Studer, Telefunken, Ampex, etc)

BE CAREFUL!AVOID:
  • use large reels or professional pancakes in domestic recorder can seriously damage recoreder mechanical parts; 
  • mix different kind of reel (plastic and metallic) and/or different diameter (5" and 10.1/2" i.e.) can damage both tape and mechanical reel parts except in some professional recorder which can manage different kind of reel at same time (i.e. some Otari models, Nagra T Audio, etc.)

DIFFERENT KINDS OF TAPE

In few words there are two kinds of tape: obsolete acetate tape and new polyester ones. They can simply recognize acetate tapes from polyester ones watching the reel in backlight: the acetate tape will look transparent. Older polyester tapes had shiny reverse side and matt magnetic coated surface; newer ones (starting from 1970 about till today) had black matt reverse side and magnetic coated shiny surface. In every kind of tapes the magnetic coated side has to face the heads.

Knowing the right kind of tape you are working on is very important in restoration to avoid damages due to wrong procedure. Different kind of tapes have different physical and chemistries characteristics and have to be treated in different ways.

Photo: courtesy by Eddie Ciletti www.tangible-technology.com

Over the years different kinds of metal oxide were tested and used to improve tape quality reducing the signal noise ratio, print trough, distortion and improve dynamic. Each tape was slightly different from the other and every manufacturer suggested the different BIAS and level settings better fit their tape.

Basically speaking the so called BIAS, in magnetic recording field, is an high frequency signal (usually from 100,000 to 150,000 hz about or higher) recorded on the tape at the same time of musical signal. This principle, discovered in 1940 by accident, dramatically improves distortion and high frequencies response giving a very high quality recording.
The Bias frequency is even the same but its level has to be adjusted according to different kind of tapes and speed (see table below) for the best MOL (Maximum Output Level) with less THD (Total Harmonic Distortion).
This is why the reel to reel recorder has to be aligned according to the kind of tape used for the best recording result.
Table shows BIAS recommended setting reffered to Studer rec and play heads. It has to be used as guide only not as absolute reference for all the open reel recorders.



Most used tapes cross reference list both for recording and BIAS level.

Most used audio magnetic tape cross reference list
www.soundfan.it
USE AGFA AMPEX/QUANTEGY BASF/EMTEC/RMGI MAXELL ZONAL 3M/SCOTCH
BACKCOATED TAPES
Studio Mastering
+9db level SP - 499 GM / GP9 SM 900 - 999 996
+6db level SP PEM 468 456 GM SM 911 or SM468 - 700 986 (old 966)
+3db level SP - 406 - XL35-90B/180B
675 206
Master-Broadcast
+6db level LP - 457 GM LPR 35 - 840 987 (old 967)
+3db level LP - 407 - XLI35-90B/180B - 207
Low print SP - 478 PER 528 - 675 -
Low print LP - - PER 368 - - -
SP
- - - - 820 -
SP - - - - 830 (*W) -
NON BACKCOATED TAPES
+6db level SP - 632 LGR 50 UD 35 - 90 844 -
+6db level LP - - - - 845 -
Note:   SP= Standard playing LP= Long Playing *W=white coated



Except Rmgi and ZONAL tapes still in production the most part of the above listed tapes are dismissed but sometimes you can find them used or NOS on the market. If you are looking for these kind of tapes be very careful: uninformed buyer can buy damaged or unsuitable tapes for music recording.
!  BE CAREFUL  ! AVOID:
buying tapes for data or instrumentation use as Ampex/Quantegy 467 or 797, 799, and 3M/Scotch 8207. These tapes DON'T WORK FOR AUDIO USE.
Pay attention to the "sticky syndrome" tapes as Ampex 456 457 406 407 produced from '75 to '85 and 3M/Scotch 226 227.
Some other tapes not defective but poor quality are
Sony SLH and AGFA PEM469 (which is nothing at all like very good 468).

At least: a basic difference in professional field is the high or low reprinting tape. High reprinting tape: expensive, high quality, low heads consumption but little echo effect on the blank part of tape (the so called "print through" effect). Low reprinting tape: cheap, low quality, high heads consumption but no or very low print through.


TAPE CARE AND HANDLING TIPS.

Magnetic tape is a strong enough support: you can record it several times and play back one time more, cut and paste with proper splicing tape for editing, but it needs some basic care suggestion.
  1. First of all AVOID ABSOLUTELY MAGNETIC FIELDS NEARBY THE TAPE (like these from TV, loudspeaker, dynamic microphone, electric and microwaves oven, electric transformers, etc.). Magnetic fields can partially (or in worst case completely) erase a recorded tape.
  2. Avoid dust collected on tape which damages tape and heads too. After use don't leave the tape unused on the recorder, recover it in its box and store in upright position.
  3. Tape recorded in one way only (full, half and multi tracks) have to be stored wound on the right reel with the start inside of the reel, avoiding to rewind tape at the end of playing. This has three advantages: reduce the print through effect which, if present, is masked by the original reverberation effects of the program; have a perfectly non mechanical stressed wound tape; they have to rewind the tape before playing this further reduce the print trough effect and "refresh" the tape.
  4. As for every media support like vinyl and CD too, avoid to touch the recorded tape with fingers, expose it to direct sun light, in smoking places and to dust.
  5. A total erasing with an external bulk eraser is recommended to full erase a blank tape and set it in pristine conditions.
  6. Last but not least the recorder has to be maintained cleaned and in perfect functional condition, right aligned both mechanical and electrical. This avoid damage the tape by stretching it, depositing debris on its surface, having poor bound on the reel and poor quality recording.

Above: two perfectly wound tapes.
Below: on the left tape wound in wrong way - on the right usual distortion due to wrong wound and high temperature storage.

The main problem is storage the tapes for long time at 40 to 90 degree F (average about 70 F) and relative humidity (40 to 60 %) as recommended by manufacturers. Sometimes it could be difficult to obtain both conditions in a non climate controlled room (like a cave or an attic where maybe you can find your dad tapes! :-))
  • Elevated temperature affect the layer to layer print through of the recorded signal, can cause layer to layer adhesion and tape backing deformation.
  • High humidity can cause, in many tapes manufactured from 1970 to 1985, the loss of glue (you will have the so called “sticky” tape) which damages definitively the tape and hardly soils the heads, capstan shaft and tape guides till to stops the tape running and damages the recorder too.

The effects on tape guides and heads due to a sticky tape rewound for 30 sec only and played for 5 second only!As you can see the dirty is not the usual "good smooth brown" collected after some month of normal use, but an hard, white /brown mixture of of magnetic fibre and dust very hard to clean.

To the contrary a well preserved, average used, 50 years old tape plays as brand new!


TAPE LIFE

Magnetic tape is still the best archiving support ever made. It is safe and durable (still used in the airplane black boxes)
The real problem about life duration of all media supports, tapes included, is the faster obsolescence of the hardware to play them than the life of the support itself.
Magnetic tape doesn't came obsolete because RtR recorder can ever been built with standard mechanical and electronics components. Technicians and ordinary people go crazy these last years to store all their data every time a new digital system came on the market because of its incompatibility with the precedent one "built to last" . . . some months :-)
Do you remember what happened to the vinyl disc when CD arrived on the market? None factory build turntables more but there were millions vinyl discs still around the world to listen to.
The same thing happened with the reel to reel recorders production stopped when digital recording went on the market. But there are hundred millions hours of recordings on magnetic tapes, not only music but the entire human history of the last century is recorded on analogue audio and video tapes.
Vinyl discs have been discovered again these last years and now many factories are producing again every kind of turntable and vinyl discs.
Many tape recorders have been destroyed in the '90es but many still stay around, jealousy conserved by their owners or restored by technicians and audio analogue lovers like me.
They will became more and more precious in the future.



TAPE RESTORING

If you discover your tape is damaged might is not too late to play it again! There are some restoring and rescue methods to play a damaged tape just one time more to copy it or migrate to a digital support.
One of the most common problem are the "sticky" tapes. The method to restore “sticky” tapes comes from an Ampex patent of 1989 the so called “baking” tape procedure. This apparently simply method has to be accurately set in practice according to the kind and tape condition to avoid damage the tape definitively (CAUTION: AVOID TO USE WITH ACETATE TAPES).
Be careful using the grand ma oven or a dryer in a box because:
  1. temperature has to be fine adjusted and controlled (about +/-45F of the set temperature) a condition you can obtain only with a professional lab oven or dryer;
  2. some electric oven have STRONG magnetic field which can erase the tape;
  3. but the worst thing is the chemical vapours of the tape can fix to the oven wall stopping your grand ma making your preferred pie :-D 
Very interesting news about professional tapes restoration are in Audio tape restoration site by Richard Hess.

I'm fully equipped to read every kind of tapes without noise reduction system or with Dolby A, B, C, S, SR, DBX, TELCOM noise reduction units. I can process old no coded tapes with a professional denoiser too.
I can transfer analogue tapes into digital or new analogue tapes with professional analogue studio machine or digital A/D up to 24 bit 196Khz using worldwide acclaimed professional HiEnd Benchmark devices.

Feel free to
contact me if  you need tape restoring and/or a backup copy.


TAPES AND ACCESSORIES

I have in stock news tapes, NAB adapters and many other accessories for open reel recorders.
Sometimes some recorder too.
Please refer to the
UPGRADE - ACCESSORIES -SPARE PARTS page.
       

SOUND QUALITY: see ANALOGUE VS DIGITAL page.



               

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