Production Year 1964 at $24.95 or in kit form at $14.95
The Hallicrafters model HD-1 capacitance decade box is used for the selection of capacitors in the range of 0.0001µF to 1.0µF. The HD-1 is capable of selecting any value of capacitor in this range in steps of 100µµF, or 100pF as it is known today. This gives the unit a a total of 10,000 different capacitance values. The unit is capable of delivering these capacitance values with an accuracy of plus or minus of 10%. The maximum continuous voltage that could be applied to the HD-1 is 350 volts. The unit has a total of 16 slide switches and three banana jacks on the front panel. Each switch is connected to one of the 16 internal capacitors and is used to simply add or subtract capacitance to achieve the desired value. Both of the red binding posts are connected to the internal components of the device. The single black binding post is a ground for the case itself. The HD-1 is encased in a metal cabinet.
So what on Earth is a Decade box and what are they used for? The decade box is a powerful tool in the arsenal of the electronic technician. There are many different types and styles of decade boxes such as those used for resistors, coils, and like the one featured on this web page, capacitors. A capacitor decade box is a device containing capacitors of many different values with some type of mechanical switching mechanism that allows the user to dial in numerous individual capacitance values. In the case of the HD-1, a total of 10,000 different values can be delivered. This makes for a very convenient way of selecting and quickly changing a capacitance value in a circuit for repair, experimentation, and development work.
The decade box easily allows the electronic technician to vary the individual values of the needed component. The values are often made in submultiples and multiples of ten which is where the unit gets its name. This is normally accomplished by the use of dials or slide switches on the decade box. The decade box can easily be set to any desired value within its operating range.
The device is useful due to it being able to quickly substituted into a circuit any standard value component. It can also be used to find the optimum component value for the best circuit operation. A resistor, capacitor or coil of the size indicated by the decade box is then implemented into the circuit. This eliminates a lot of circuit splices from the cut and try methodology. A good application for the decade box is in the use of precision bridge measurements. For example, the value of a balance resistor needs to be very accurately determined. This is where a decade box really shines because trying to find the ohm value by using a variable resistor or a logarithmic taper or law potentiometer is often difficult due to it not being sufficiently linear to guarantee a precise ohm reading.