Compared to EI-chokes, our toroidal chokes have at least two major advantages: they have smaller external magnetic leakage fields and they make less acoustic noise. The reason why is found in the circular shape of the core in which all the magnetic field lines are captured and the special core construction, making acoustic vibrations almost impossible.

Our chokes can be divided into two groups: the CLC-chokes and the LC-chokes.

The CLC group is meant for those applications where the tube or semi conductor rectifier of the high voltage is followed by a buffer capacitor C1. After that the choke L_CLC is placed plus another buffer capacitor C2. See figure 1. This "pi-type" structure uses the choke as impedance to stop the fundamental and harmonics of the mains voltage, thus creating a pure DC voltage with almost no ripple on it.

*: For other Idc and Vac,rms values, please refer to the text and the figures 3, 4, 5 and 6.

The table above summarizes the specifications of the chokes. The 50 mA chokes are meant for tube pre amplifiers. The 100, 200 and 400 mA chokes will find their application in tube power amplifiers. The inductance of each choke equals 10 H (with the exception of choke PAT4171 with 20 H). The DC resistance of the chokes is remarkably small, resulting in little heat loss inside the choke.

Due to the low stray fields, the position of toroidal chokes inside an amp is not very critical. It is advised to keep some reasonable distance away from sensitive input circuitry. The single-screw mounting makes it very easy to place the choke on the chassis, horizontally or vertically The size of a toroidal choke is comparable to an EI-choke of equal value. Normally toroidal transformers are smaller than EI- transformers. However, we have used larger toroidal cores to prevent any saturation and to create a wide safety margin.

In the group of CLC chokes, the specified DC current is the maximum current. Smaller DC currents are always allowed, while maintaining the inductance value specified. No maximum AC voltage is given. We assume that the buffer capacitors C1 and C2 are large enough for negligibly low ripple voltage.

In the group of LC chokes, two specs are given; the DC current combined with the AC rms voltage from the high voltage winding of the power transformer. However, per LC choke other currents and voltages are allowed as long as certain limits are not surpassed. These limits are shown in the figures 3, 4, 5 and 6. The graphs indicate that higher currents are allowed as long as the AC voltage is smaller and vise versa.

A short explanation might help to understand this important feature. Inside the choke core, a part of the total magnetic flux headroom is used for dealing with the DC current, while the residual magnetic flux is used for handling the AC rms voltage. Suppose that there is less current demand, then the residual flux for the AC rms voltage is higher and higher AC voltages are allowed. Take as example figure 5 of the PAT4177. A maximum 200 mA DC current is allowed at an AC voltage of 450 Vrms. However, at 1000 Vrms a maximum DC current of 90 mA is allowed without core saturation. This means that one freely can select its own operating point on or under the limiting line while staying within the safety margins of the choke. Therefore, our LC chokes can be used in a wide range of current and voltage applications with a constant inductance as specified.