Hi, I'm that Hondaman from the SOHC4 forums! Someone asked me to drop by with some explanation about the Transistorized Ignition.
It's an old design from the 1970s, updated in 2006 to use modern components. The box itself is 2" x 4" x 1" thick, normally with the wiring coming out the short side, but other custom configurations are available upon request, including a SPTT center-off toggle switch to kill it in case someone wants to hotwire your vintage bike for someone else's ride...
This box detects the temperature of the points baseplate to provide a stronger spark for cold-start, and then it backs off that mode as the engine warms up, and slightly extends the spark duration (as compared to stock) by more smoothly buffering the back_EMF from the coil(s). This helps with many vintage bikes as a too-short spark duration was very common in the older designs, particularly those where 2 sparkplugs are fired by one coil. The power to the points is less than 0.1 amp and the power transistors can handle up to 5 amps for coils like the Dyna 3-ohm units if you wish to run those. It is not a simple switch like the one shown above: instead this one will run in systems from 4.6 volts to almost 28 volts power situations. These have been in use on the Honda SOHC4 bikes since 2006, and apart from a batch of bad power transistors I received from Malaysia in 2011 (I think it was) when all 25 units built with them failed in less than 5 hours of operation, only 2 other units have ever died in normal use. Both of those were miswired first, which damaged the transistors inside, so then they failed shortly after being wired correctly. It is a very old and tested design.
If you're interested in one, drop me an e-mail at
SOHC4shop@gmail.com. My website at SOHC4shoo has been 'down' along with some 10,000 other server users there, since last month: I'm working on getting a new website built. Something apparently happened to seriously damage the OS Commerce group in the computer farm in Ireland last month, where we all were hosted.