Ground Reverse Alternative

[UltraHookedOnPhonix]

In light of HADs use of a "1-N-2" Ground switch, it's a known fact that all reverse polarity switches are a safety concern since the capacitor that's supposed to filter the AC line can be leaky or become so with age.
Something struck me as a viable alternative to this antiquated way of filtering line noise. Namely, common-mode filters or EMI filters.
[IMG:200:60]http://i205.photobucket.com/albums/bb17 ... Filter.gif[/img]
These line filters fulfill the same purpose as the polarity switches and are deemed safe (UL approved). A single stage EMI filter includes three caps (one is across-line and two are line-to-ground) and a common-mode choke of small inductance like the one from Qualtek in the attached PDF file.
What's good about the caps in this filter is that the maximum leakage to ground is .25mA (115VAC @ 50Hz) and if they were to fail, they'll open like a fuse instead of shorting which in turn creates the dreaded "hot" chassis.
I suppose if one wants to, they could simply substitute a class Y2 (line-to-ground) cap for the .047uF "Death cap" and essentially have a safe 1-N-2 ground switch. Read more about safety caps here: www.justradios.com/safetytips.html

Happy New Year to all Amp Garage members!
-UltraHookedOnPhonix-

[ic-racer]

That is an interesting solution. I am working on some vintage HiFi stuff now and have needed to reverse the plug on occasion. Thus the need to either keep the two prong cord or hook up a ground switch.

For my guitar amps with a ground switch, I make sure the fuse is in between the cord and the switch. Thus, the fuse will fail if the death cap fails. If I were paranoid of mis-wired service lines, a second fuse, on the other line would blow in the unnusual case of a mis-wired service line and a failed death cap.

[UltraHookedOnPhonix]

For my guitar amps with a ground switch, I make sure the fuse is in between the cord and the switch. Thus, the fuse will fail if the death cap fails.

That'll work unless you have a leaky death cap which won't blow the fuse. It looks to me that just substituting the normal PVC/orange drop variety for an application specific line-to-ground safety cap will take care of the problem. I'd never trust "normal" caps in those relatively high AC applications where they live under constant load. Obviously, HAD did but it's a dance with the devil!
Another unsafe way ODS amps were built was that some amps had a "convenience" outlet (some MM amps too?). When using this add-on outlet there's juice on the power chord prongs that are dangeling from the head cab.
Someone correct me if I'm wrong but looking at the schematics would lead me to believe it's wired that way...

Safe 2009

[UltraHookedOnPhonix]

Here's a class Y2 capacitor offering from Evox Rifa that looks good for "Death Cap" applications/substitutions:

Mouser part#: 80-PME271Y547MR30

Downsides: rather big, pricey and with a +/-20% value tolerance.

[Structo]

Aren't those available as well in the IEC format?

[Structo]

Like this?

http://www.mouser.com/Search/ProductDet ... eEGw%3d%3d

[UltraHookedOnPhonix]

Like this?

Yeah! Or you can use chassis mount filters if you're using a strain relief receptacle for the power chord.