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?DaveMerrick wrote, on one of the Hammond mailing lists:

Actually the "Death Caps" in Leslies should be replaced with modern type Y2 "SAFETY CAPS" Better known as "AC Line RFI Suppression Capacitors" These are relatively "new" types and I'm finding not a lot of techs know about them. Type Y are for Line to Chassis-Ground applications. Type X are for Hot-to-Neutral Applications.

Both type Y2 and X2 go on the power transformer primaries and must have UL listing UL1414 (In the US) or EN60950 (in Europe.) IEC950 Is the International Standard. The Idea is that a Y2 safety cap has enough insulation to keep from shorting out. (And Killing you) In older gear you will typically see Mica, Paper Wax, or even film types going between the transformer primaries and chassis ground. These older types of caps make no provision for failure. They work good, until they do (And they will) short. Then you have Mains AC directly connected to chassis. Obviously NOT GOOD! The purpose if line filtering/Interference Suppression caps are there in the first place is to send High Frequency interference signals present on the AC Line to ground. Today these suppression caps are even more needed than they were 30 years ago. Most modern electronics uses switching power supplies (Most of them of mediocre design). Originally the only Harmonic injection we had to worry about was from florescent/neon lighting, but now because almost everything has a switching power supply, harmonics are being injected into the mains wiring like never before. In fact in they are now beginning to recommend that the neutral line in new building wiring be double in gauge in order to handle the sheer amount of odd-order harmonics (additive) injected back into the neutral. Switching power supplies introduce a ton of high frequency noise back into the mains wiring of a building (Especially the Neutral). Even though TYPE X&Y caps are designed for mains applications, I'd still insert a fuse in series with them (Just in case)

Dave Cantelon has a great "non-tech" primer on using class X & Y safety capacitors in vintage tube equipment. at

ALL Techs should read and understand this document: * A Datasheet of some X&Y Types: * Another Manufacturers Info: *

Here's some interesting additional reading on mains harmonic injection: * * * * *


MouserElectronics P/N 75-F17103471000 seems to fit the bill for Leslie death cap replacements.


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