Henry 2K-4 / 3K-A 2K Classis

Henry 2K-4 / 3K-A / 2K Classic


Soft-Start is a term describing any electrical circuit which reduces excess current during initial power-up.

The SS-100 Universal Soft-Start kit by Harbach Electronics  works perfect for Henry RF amplifiers. The SS-100 mounts inside the RF amplifier and places a small resistive load in series with the AC mains, greatly reducing inrush current. After a short delay determined by the on-board L/C circuit, the resistive load is switched-out of the circuit by the two relays. This safely limits inrush current to protect hard-to-find and costly-to-replace switches, tubes, filter capacitors and high voltage transformers. The SS-100 comes default with two 20-ohm 10-watt power resistors for 220VAC mains operation. If the amp is operated on 110VAC mains, the resistors must be changed to 10-ohm 10-watt.


Showed in the following pictures, the soft-starts are wired for 240v 3 wire configuration. A 240V 3 or 4 wire configuration are basically the same. A 4 wire configuration has two ground current paths, one is for the return (120/0/120) ground voltage side and one for earth/chassis ground. For a 3 wire configuration, both the return and earth ground current paths are on the one same wire. For a 4 wire system,  to wire the soft-start, tie the two grounds together, resulting in a 3 wire configuration.

Henry 2K Classic

Connect the Soft-Start in series with the two 240VAC power connections feeding the HV transformer terminals. Note the required green ground wire to chassis ground.



Henry 2K-4 / 3KA

Connect the Soft-Start in series with the two 240VAC power connections feeding the HV mercury relay input.



For other Henry amplifiers, reference the amplifier's schematic and adjust the installation as required.



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