high voltage diodes ?

[LilBill]

i want to make some msd wires to run on a dual plugged mag setup and i'm having trouble finding the diodes. the book i'm following just gives these values "75000v and 250mA" i tried googling with no luck and none of my local electronics dealers were any help. anybody know a source for these or have a part number ? buck at goblinmillworx had them but i guess he's not around anymore ?

[nc-renegade]

Believe it or not, a good source for these diodes old microwave ovens.  At 75K voltage breakdown, you will have to run several in series though.

There are others rated at very high voltage, but low amperage.  With these, you would have to parallel them to get the current rating you want.

Here's a link that I found a while back, it list that above as a reference and provides several places to look:


http://amasci.com/tesla/diode.html

[PC_Hater]

Interesting problem.
There don't seem to be any sensible diodes that do that.
For example www.hvca.com have diodes that will handle 90KV reverse voltage at 25mA but the diode is 3" long.

Something isn't doing what I think it is!

What are 'msd wires'?
Dual-plugged mag setup I think I understand. You want to run two plugs in one cylinder head from one magneto? Or as it is a Harley, a pair of twin plug heads.
Even then, I can't think why the diode would need to handle 250mA?

You can get away with diodes in series but be careful with diodes in parallel. The current is never equally shared between them so there is always one that takes the lion's share and fails early.

[Coyote]

You can get away with diodes in series but be careful with diodes in parallel. The current is never equally shared between them so there is always one that takes the lion's share and fails early.

[LilBill]

Sorry, that's MSF (magneto single fire) not MSD (multi spark discharge) , had a senior moment there while typing up my question. Here's a link to one that J&P sells http://www.jpcycles.com/productgroup.aspx?GID=E665E998-25D0-4119-BFA0-5988EB232565
You can see in the pic that the diodes are not that big.
The values I listed were taken from a section of Bill Rooks "How To Build A Harley Torque Monster" where he describes how to build a set of these. BTW, his chapter on harley magnetos is about the best I've seen.
Buck at Goblinmillworx used to make these up and sell them so there HAS to be a source for these diodes. Buck seems to have disappeared so there's no asking him.

[nc-renegade]

Even then, I can't think why the diode would need to handle 250mA?

You can get away with diodes in series but be careful with diodes in parallel. The current is never equally shared between them so there is always one that takes the lion's share and fails early.

I too question the 250mA, perhaps 250 microamp?   You can parallel diodes if they are matched.   This is done all the time on large power inverters.

[LilBill]

What about the high voltage diode in a microwave oven ? it's rated at 75000v but i don't know about the various amp ratings ?