Harbach Electronics HINT User Manual

A HELPFUL HINT

To help protect your SB-220/221 from high voltage current transients, try making and
installing a simple HV fuse. It will protect against blown resistors on the rectifier/metering board,
destroyed plate current and grid current meters and other BAD things.

Take a small piece of circuit board material about 1½” x ½” and place a solder pad on
each end, leaving about a 1” gap between the pads. Find the HEAVY BLUE
from hole “J” of the left side of the rectifier/metering circuit board that goes to the HV feed­through insulator “CK” to the left of the circuit board. Cut this wire in the middle and solder the
ends to the pads on your HV fuse. Take a piece of small wire, about #32 to #36, and solder it
between the pads on the fuse. If you do not have the small gauge wire, you can get it from any
110VAC extension cord of the cheap variety – ONE
clear of any other components or wires. This can also be adapted for the SB-200/201.

NOTE: A good source of #36 wire is ONE

strand from a discarded computer ribbon cable.

strand is enough. Make sure the fuse is

HV wire coming