[GreenKeys] Newbie BARTG ST5 Power Supply Question?

[Brooke Clarke]

Hi:

Can someone tell me the purpose of D12 and D13 in the ST5 SU?
http://www.baudot.net/creed/docs-alan-hobbs/rtty-the-easy-way.pdf

I understand that the 3k3 Ohm resistors that they shunt set the current and 
they are back biased when the related transistor is open.

I expect that they are for shunting the back EMF spike from turning off the 
selector magnet and back on in the opposite polarity.  That would seem to be a 
problem greatly slowing down the turn off time.

-- 
Have Fun,

Brooke Clarke
http://www.PRC68.com
http://www.precisionclock.com