Brüel & Kjær Model 2301 Level Recorder

A vacuum tube based chart recorder which weighs about 35 kilograms. It comes from the damp basement of my friend Barney, and picked up some damage from that. Not that I would have tried to make it work again, it's entirely obsolete. Maybe a nice platform for something like a Paraset.

The round black thing is some kind of a linear motor that moves the pen back and forth. And it's not really a pen, just a sharp point and special paper.

The pen motion is fed back via the strip on the bottom of the "Potentiometer" box on the left-hand side.

The gearbox gives ten different paper feed rates.

The valve lineup is (left to right) a EZ2 full wave rectifier, 2 x EBL21 audio output pentodes with dual diodes (the diodes are not used), 2 x EF8 low noise variable μ pentodes, an EB4 double diode and two more EF8.

I'm not so sure that this gearbox gives the exact rates (100 / 30 / 10 / etc mm/sec) because every section looks identical. It would therefore presumably divide by the same ration every time?

resistor network

Inside the "Potentiometer" box. The assembly on the right is a dagwood of metal and insulator, with a wire from each metal plate to a different place on the (50dB!) resistor network.

resistor network bottom

The non-pen end of the shaft has a wiper that wipes along this track, that gives feedback as to where the pen is. The linear motor is massive and the pen assembly is light, this thing must have a seriously fast response time.

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