"Jasen Betts" bravely wrote to "MIKE ROSS" (13 Mar 04  07:48:31)
 --- on the heady topic of "{at}%^{at}#$%^ veroboard"

 JB> the final circuit was something like this.
 JB>
 JB>         ___________________________________________________________ +12
 JB>         |          |      |       |                |           |
 JB>        ???        10k    _L_     _L_100n   ,-[1M]--)----.      |
 JB>         |          |     /^\     ~T~       |  R7   |    |  .---|---.
 JB>         |     _____|  || ~T~ . .  |        |     |/     |  \  _L_  |
 JB>         |  |/'     |--||--+--|<|--+-[100K]-+-----|~ Q3  `-|/  /^\  RL
 JB>  ,-[1M]-|--|      /   ||     ` `     R6          |\        \  ~T~  |
 JB>  |      |  |\| |/'    1n                           |        `--|---'
 JB> _L_     |   ~`-|  Q1,2                             |          /'
 JB> ~T~     |      |\|                                 |       |/'
 JB>  |10p   |       ~`\                                |-[10K]-|   Q4
 JB>  |      |          |~~~~|                         10K      |\|
 JB> _|     2M2        3K1  _L_1u                       |        ~`\,
 JB> video   |          |   ~T~                         |           |
 JB> input   |          |    |                          |           |
 JB> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ 0V
 JB>
 JB> before I had built anything left of R6, or fitted R7 I was finding
 JB> that even connecting  the left end of r6 to +12 would not turn Q4 off.
 JB> it was then that I measured 400k between the Q3 base and collector
 JB> tracks

Thanks for the artwork. I'm assuming you are publishing your circuit
for all to see in order to get some constructive feedback, so I'll try
to be helpful.

I like the addition of the R7 positive feedback. It adds a level
sensitive trigger point to the circuit with some hysterisis. OTOH
might the addition of R7 have possibly made the circuit a little
susceptible to oscillation because of the coil inductance and stray
capacitive coupling?

The original task really boils down to 2 requirements: 1-triggering,
2-timing. Your circuit fulfills #1 very well because of the ample
input gain but I feel it neglects #2 to some extent.

However you must take my comments with a very large grain of salt
especially if the circuit in fact does exactly what it should for you!

 Mike
 ****

... Of course it's grounded!  ...watch,  ...YEEEEEAAAAAAAAHHHHHHHH!!!!
--- Blue Wave/DOS v2.30