[Amps] Crowbar components

[Frank Goenninger]

Hi all on the list:

There have now been several posts here pointing
to

http://www.qsl.net/oe5jfl/flashover.htm

as a suitable crowbar circuit. I want to copy that 
one...

When searching for suitable components I could not
find a suitable opto-coupled Diac as shown in the
mains circuit. 

My HV transformer will draw abt. 21A of current so
I need a Diac able to withstand that or I have to
substitute that part with ??? A diac controlling
a thyristor ? Or ?? 

Are there any such diacs or what would a suitable
replacement circuit not altering speed too much
look like? 

Thx for your help!

73, Frank DG1SBG