Bruel & Kjaer 7003 and 7004 Tape Recorders

This very well designed recorder was build by Bruel & Kjaer in the seventies as a battery operated portable recorder. The 7004 is a 2 track regular audio recorder and the 7003 a 4 track FM modulated recorder. With the 7003 signals from DC up to 20Khz can be recorded without distortion. It is carried in a sturdy leather case with a flip top for the person to operate the machine. The tape path is dust-proof sealed by a lid. Operation is done by means of two levers and a few buttons left and right of the tape heads.

The left lever is for fast forward and rewind. the buttons control stop and play/ record. The right lever controls Playback or record. The button releases the lever to its neutral position.

If both levers are in the 0 (off) position, the recorder is off. if one of them are set, Power is on. The recorder will not play directly after setting the right lever. it is in the pause mode. After pressing the play or play/rec. buttons on the left side, the tape will run. This seems odd, but in normal use in the field, only the stop and rec./play buttons are used and when not running, the machine is in the pause mode. The machine can be remotely set to play or pause. Underneath the right "Release" button is the speed selector. the red lights next to the switch seem a little confusing, but there is also a hidden "mode" switch under the black head protector. The "Mode" switch selects between two distict recording systems. the one marked 1.5 ips is for the IRIG recording system, used for technical mesurements. The one marked 7.5 ips is for audio recordings with the IEC system (normal audio tape recorder system) use this mode for normal audio use. in this mode, you can switch on the front between 7.5 ips and 15 ips.

Input and output are provided by 4 BNC connectors. On the 7004 only ch1 and ch2 are used. There is no direct gain control, so a external mixer has to be used for audio recording. Behind the black plate in the middle of the picture, there is a trimming spot for the four channels, but these are calibrated in the service-center, So don't use them, unless you really want to. The DC setting of a channel can only be used on the 7003 FM recorder, so set for AC. Note that both the tracks will be erased when recording on a 7004. on a 7003 there is no erase-head. Data can be recorded on a track basis. the 7004 has a signal to noise ratio of 55dB. the 7003 only has 30dB.

The small meter on the right can be switched to monitor the channels and battery life.

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Here you can set the tape speed. this is a three speed machine, but the switch has only two positions. the down position equals 15 ips, the up position can be preset to 7.5 or 1.5 ips. (the "mode" switch is underneath the head cover).

Of course there are the outputs, again with the BNC connectors.

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Here are the connectors for external power, remote start/stop and microphone.The microphone input is used for commenting recordings recorded on channel 1 with automatic gain. a dinamic microphone can be connected to pin 1 (hot) and 2 (earth). With a switch connected between 2 and 3 you can set the microphone to be a monitor for the signals recorded. (this provision is mainly for scientific uses where the signal recorded is not always "audio". The power connector has four pins. they are for direct power and for charging the internal battery-pack if available.

Power is done by a long battery-pack containing 6 D-size batteries. They can be changed for NiCad and can be recharged internally.The battery-pack slides in from the back. There is also a mains power unit (B&K 2808) with the same size you can use.


Here you can see the first look of the bottom after removing the bottom plate. an explanation is on the inner side of the bottom plate. There you can also see how to place the batteries is you make your own battery-pack like I had to. The 7003 is missing the small pcb on the left middle. Its the erase oscillator board. when the main pcb is removed (3 scews of two different types! be aware where to put them) you get a look on the beautiful drive belt.

The main drive belt is of a small film type. Adjusting the tension is done with the small wheel here seen under the black bar in the middle of the picture. But if its not necessary, don't do it. The round metal thing on the right with the three red dots is'nt the motor but the tachometer to monitor the speed. You can clearly see the two capstans on the left (the ones with the big holes) and the central drive pulley in the middle.

In the top-left corner you can see the main fuse of the machine. as stated on the picture below it is a 2.5A slow blow type.