what fires the 2n5064 in the crowbar circuit? looks like the 2 gates are
tied together and go nowhere else. how does that make a diac?


"Eeyore" wrote in message
...

TimPerry wrote:

what fires the 2n5064 in the crowbar circuit? looks like the 2 gates are
tied together and go nowhere else. how does that make a diac?

You know, I'd never looked at that in detail. That's puzzling.

I do indeed use a diac myself in that application. Look at the Behringer EP2500
schematic, they copied it 'verbatim'.

Graham

"Eeyore" wrote in message
...


TimPerry wrote:

what fires the 2n5064 in the crowbar circuit? looks like the 2 gates
are
tied together and go nowhere else. how does that make a diac?

You know, I'd never looked at that in detail. That's puzzling.

maybe leakage at the p-n junction on one is enough to fire the gate on the
other under full DC conditions. just a wild guess.... or maybe the
schematics are just plain wrong. it's not uncommon, unfortunately. i don't
feel like tearing mine apart just for curiosity's sake.


I do indeed use a diac myself in that application. Look at the Behringer
EP2500
schematic, they copied it 'verbatim'.

Graham


any chance you have a QSC USA 850 schematic? a DJ blew mine up. i don't use
to anymore except as a loaner but im sentimentally attached to it.

"TimPerry"

any chance you have a QSC USA 850 schematic? a DJ blew mine up. i don't
use
to anymore except as a loaner but im sentimentally attached to it.


** All QSC's shems are here.

http://www.qscaudio.com/support/tech...rt/schems1.htm






........ Phil

"Phil Allison" wrote in message
...

"TimPerry"

any chance you have a QSC USA 850 schematic? a DJ blew mine up. i don't
use
to anymore except as a loaner but im sentimentally attached to it.


** All QSC's shems are here.

http://www.qscaudio.com/support/tech...rt/schems1.htm






....... Phil


thank you Phil, this explains why one channel remains functional with one
internal fuse blown.

"TimPerry"

what fires the 2n5064 in the crowbar circuit? looks like the 2 gates are
tied together and go nowhere else. how does that make a diac?


** It doesn't - as a rule.

Just tried two GE brand C106D1s ( 400 volt, 4 amp sensitive gate SCRs)
connected as shown in the QSC schem.

Functioned like a pair of soggy, 18 volt zeners wired back to back.





........ Phil

TimPerry wrote:

any chance you have a QSC USA 850 schematic? a DJ blew mine up. i don't use
to anymore except as a loaner but im sentimentally attached to it.

I'm sure it's at qscaudio.com, under support.

Graham

Phil Allison wrote:

"TimPerry"

what fires the 2n5064 in the crowbar circuit? looks like the 2 gates are
tied together and go nowhere else. how does that make a diac?

** It doesn't - as a rule.

Just tried two GE brand C106D1s ( 400 volt, 4 amp sensitive gate SCRs)
connected as shown in the QSC schem.

Functioned like a pair of soggy, 18 volt zeners wired back to back.

Hardly the best substitute for a low voltage diac !

Graham

"Eeyore" wrote in message
...


Phil Allison wrote:

"TimPerry"

what fires the 2n5064 in the crowbar circuit? looks like the 2 gates
are
tied together and go nowhere else. how does that make a diac?

** It doesn't - as a rule.

Just tried two GE brand C106D1s ( 400 volt, 4 amp sensitive gate
SCRs)
connected as shown in the QSC schem.

Functioned like a pair of soggy, 18 volt zeners wired back to back.

Hardly the best substitute for a low voltage diac !

Graham


it might be that purchasing got a really good deal on 5064's.

i wonder what happens when the NP cap goes bad. it fires every half cycle?