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 HV wire coming 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 strand is enough. Make sure the fuse is 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. ...