I sent this:



Greg

The flasher circuit shown on this webpage

               http://www.gregsbasicelectronics.com/circuits/ledoscillator.=
htm

and on the cover of your introductory book and elsewhere, cannot work
in any reliable or repeatable sort of way.

The two resistors from transistor bases to ground should be from bases
to V+. Without this arrangement the transistors will not have forward
bias and the circuit will not start. It may be able to be made to run
if certain actions are performed but it is NOT a proper astable
multibibrator as shown.

The attached images show a large number of 2 transistor astable
oscillators (google image search) and, as you will see, ALL these (or
all that I noted) use formal forward base bias.

If it DOES start it is because the leakage current through the
capacitors is very high by normal standards. eg to get the bases to
say 0.5V needs I =3D V/R =3D 0.5/ 10k =3D 50 uA.
Low quality caps may exceed that level, but standard caps from eg
Panasonic, Cornel-Dubilier and Kemet have lower or utterly marginal
leakages.

See also circuits here:

           http://bit.ly/TransistorAstables

_______________

SK - won't work
http://www.cde.com/catalogs/SK.pdf

Panasonic Type A series M - no
http://industrial.panasonic.com/www-cgi/jvcr13pz.cgi?E+PZ+3+ABA0012+ECA1CM1=
01I+7+WW

Nichicon VR - just maybe
http://www.nichicon.co.jp/english/products/pdfs/e-vr.pdf

SMG may work :-)
http://www.chemi-con.co.jp/e/catalog/pdf/al-e/al-sepa-e/004-lead/al-smg-e-1=
11201.pdf




      regards


                      Russell McMahon
--=20
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