Magnetic Tape Recorder Heads

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Chapter 3

Magnetic Tape Recorder Heads

Learning Objectives

After completing this chapter, you'll be able to do the following: 1. Describe the construction, function, and placement of magnetic tape recorder record, reproduce, and erase heads. 2. Describe the preventive maintenance requirements for magnetic tape recorder heads.

Magnetic Tape Recorder Heads

Magnetic tape recorder heads are the heart of magnetic tape recording, because it's the magnetic heads (as we'll call them in this chapter) that actually: 1. Record signal or data information onto magnetic tape 2. Reproduce (play back) signal or data information from magnetic tape 3. Erase any signal or data off of magnetic tape To do these things, a magnetic tape recorder can have up to three different heads installed: one head for recording, one for reproducing, and one for erasing. Some magnetic tape recorders will use the same head for both recording and reproducing. Figure 3-1 shows a typical multitrack magnetic head.

Figure 3-1.—Typical multitrack magnetic tape recorder head. 3-2

Magnetic Head Construction

Magnetic head construction is basically the same for all magnetic heads. They're all made up of a magnetic core wrapped with a coil of very thin wire. But, there's where the similarity ends. From here on, each magnetic head is built to perform a specific job. Will the head be used on a single track recorder? Will it be used on a multitrack recorder? Will it be a record head or a reproduce head? Or, will it be an erase head? What frequency will it be recording and/or reproducing? The answers to these questions will determine the final construction of a magnetic head.

Figure 3-2 shows the construction of a typical multitrack magnetic head. Magnetic cores are wound with very thin wire, cemented together, and placed inside a half-bracket. A tip piece is then placed on top of the ferrite core, and the two half-brackets are assembled together. It's during this final assembly process that the headgap and the resulting frequency response of the magnetic head are determined. After some final contouring to give the magnetic head its curved face, it's ready for use. Figure 3-2.—Multitrack tape recorder head construction.

3-3 Record and Reproduce Heads Record and reproduce heads convert and transfer electrical signals onto and off of magnetic tape. The maximum frequency these heads can transfer depends on the size of the headgap and the speed of the magnetic tape (we'll discuss speed in the next chapter). Most record and reproduce heads are in one of these three general bandwidth categories: 1. Narrowband—100 Hz to 100 kHz 2. Intermediate band—100 Hz to 500 kHz 3. Wideband—400 Hz to 2 mHz The only physical difference between a record head and a reproduce head is in the number of turns of wire on the core. A reproduce head will have more turns than a record head. This is because reproduce heads must be able to recover low-level signals from magnetic tape. The extra turns of wire allow the reproduce head to output the highest level possible and at a good signal-to-noise level.

Record heads are always placed before reproduce heads on magnetic tape recorders. This allows you to monitor signals that you're recording. Figure 3-3 shows the placement of record and reproduce heads. Figure 3-4 shows some of the typical track arrangements used. Figure 3-3.—Placement of magnetic tape recorder heads. 3-4 Figure 3-4.—Magnetic head track placement. Erase Heads Erase heads transfer a signal to the magnetic tape that causes the magnetic particles to assume a neutralized or erased state. To do this, a high current signal that is 3 to 5 times higher in frequency than the maximum frequency response of the record and reproduce heads is used. In some audio recorders, a simple direct current (dc) voltage is used.

Erase heads are always placed before the record and the reproduce heads on tape recorders. This allows you to erase the magnetic tape before it's recorded on. Figure 3-3 shows the placement of erase heads. Q-1. Magnetic tape recorders can have up to three different heads installed. What are the three functions performed by a recorder's heads? Q-2. The way a magnetic head will be used determines how it is constructed. Name three factors that determine the final construction of a magnetic head. Q-3. What two specifications determine the maximum frequency that a recorder's record and reproduce heads will be able to transfer?

Q-4. Most record and reproduce heads are in one of what three bandwidth categories? Q-5. Why are record heads always placed before reproduce heads on recorders? Q-6. A recorder's erase head is always placed in what sequence on the record/reproduce track? 3-5

Magnetic Head Maintenance

It's very important to regularly maintain magnetic heads. If you do, you'll greatly reduce the chance of getting a poor recording or playback. Regular preventive maintenance will also increase the life of the magnetic heads. There are two things you must do to properly maintain magnetic heads: (1) keep them clean, and (2) keep them demagnetized. Cleaning Magnetic Heads Through use, magnetic heads pick up dirt, dust, lint, and oxide particles from the magnetic tape. These particles collect on the magnetic head and, if left unchecked, could cause signal dropout errors that degrade the quality of recording and playback. To keep magnetic heads clean, regularly clean them with a cotton-tipped applicator soaked in either isopropyl alcohol or in a magnetic head cleaner recommended by the recorder's manufacturer. A good rule of thumb is to clean the heads each time you change a tape reel or cartridge.

Demagnetizing Magnetic Heads Magnetic heads can become magnetized from many sources. It could happen • during ac power losses, • during testing or alignment, • because of stray magnetic fields, • from normal use. No matter the cause, magnetized magnetic heads degrade the quality of the magnetic recording or playback. To demagnetize magnetic heads, you'll use a hand-held degausser. It could be like the one shown in figure 3-5, or like the manual degausser shown in the previous chapter. No matter how they look, they all generate an ac magnetic field that demagnetizes the metal parts of a magnetic head.

3-6 Figure 3-5.—Hand-held head degausser. The procedure for demagnetizing a magnetic head is similar to the procedure for degaussing a magnetic tape. Here are the basic steps: 1. Remove the tape (reel or cartridge) from the magnetic recorder. 2. Holding the degausser an arm's length away from the magnetic head, energize the degausser. 3. Slowly bring the degausser closer and closer to the magnetic head. Don't touch the head with the degausser. 4. Move the degausser back and forth across the head for 15 to 30 seconds. Figure 3-6 shows how this looks.

5. Slowly move the degausser away from the magnetic head. When the degausser is an arm's length away, de-energize it. 3-7 Figure 3-6.—Demagnetizing magnetic heads with a degausser. That's all there is to it. It's hard to determine exactly how often magnetic heads should be de-magnetized. Manufacturer's recommendations vary from every 8 to 25 hours of operation. To be safe, check the equipment's technical manual. Q-7. What two preventive maintenance actions must you do regularly to increase magnetic head life and to ensure good tape recording and playback?

Q-8. How should you clean your recorder's magnetic heads? Q-9. What are four sources that can cause magnetic heads to become magnetized? Q-10. What type of equipment should you use to demagnetize your recorder's magnetic heads? Q-11. How often should you demagnetize a recorder's magnetic heads? SUMMARY Now that you've finished chapter 3, you should be able to (1) describe the construction of magnetic tape recorder heads; (2) describe the purpose and placement of record, reproduce, and erase heads; and (3) describe the preventive maintenance requirements for tape recorder heads. The following is a summary of important points in this chapter: Magnetic tape recorders have up to THREE MAGNETIC HEADS to perform the erase, record, or reproduce function.

Three factors that determine the CONSTRUCTION OF A MAGNETIC HEAD are the (1) type of head, (2) frequencies it will record, reproduce, or erase, and (3) use on a single or multitrack recorder. 3-8 Most tape recorder heads are designed for ONE OF THREE BANDWIDTHS: (1) narrowband, (2) intermediate band, or (3) wideband. A recorder's magnetic heads are in the following SEQUENCE on its record/reproduce track: (1) erase, (2) record, and (3) reproduce. Two important PREVENTIVE MAINTENANCE requirements for magnetic heads are cleaning and demagnetizing.

Answer To Questions Q1. Through Q11.

A-1. Record, reproduce, and erase. A-2. a. Type of head (record, reproduce, or erase). b. Frequencies it will record or reproduce. c. Whether it will be used on a single or multitrack recorder. A-3. a. Size of the headgap. b. Speed of the magnetic tape. A-4. a. Narrowband—100 Hz to 100 kHz. b. Intermediate band—100 Hz to 500 kHz. c. Wideband—400 Hz to 2 mHz. A-5. Allow you to monitor the signals you're recording. A-6. First, before the record and reproduce heads. A-7. a. Keep the heads clean. b. Keep the heads demagnetized.

A-8. With a cotton-tipped applicator soaked in either isopropyl alcohol or a head cleaner recommended by the recorder's manufacturer. 3-9 A-9. a. During ac power losses. b. During testing. c. Because of stray magnetic fields. d. From normal use. A-10. A hand-held degausser like the manual degaussers used for degaussing magnetic tape. A-11. Every 8 to 25 hours depending on the manufacturer's recommendations.