The PNP transisotrs used in the old Mag Pulse system were used for several reasons. In the day, High current transistors wete not cheap nor plentiful. Besdies, they used germanium for another reason that was not widlely published outside of an obscure SAE paper that I latched on to while we were experimenting with the Mag Pulse in my early stock car racing days.
The Germanium's were selectively sourced by GM in the day so that they worked as part of an integrated system. If you used generic replacements, you might not get the same advance curve as a factory spec'd amp might give.
Reason; They were using that germaniums transisistors to have spark fold back at high RPM. Drag racers do this via dual points where they retard ignition once they get into high gear for more power. GM was doing this by having the select fit germaniums switch slower as you went higher in the rpm range and in doing so, wah lah, spark retard without mechanical intervention..
Result was you got almost a linear spark retard as you got above 6000 rpm.
The "zero crossing" detector is also sort of unique in the circuit as this makes up for not having a bipolar supply. The zero crossing enables you to trigger on the RISE of the AC voltage that the pole piece/weight assembley signal gives to the box.
If you look hard and not too hard at that, you can take an early 4 pin HEI module and replace the guts of the Mag Pulse amp with it. IN fact, the GM circuit is exactly the same one used by Sunnen on theri now long gone distributor testors to take the distributor signal and fire the coil.
THe in line harness resistors simply limited current in case some idiot left the ignition switch on and the engine was not running.
Yes, the special mag pulse coil had a special turns ratio and it pulled lots of current. SOmthing like 8-9 amps. Some racers run them without alternators but that will limit the output voltage to the plugs. If you have a fried Mag pulse amp board, you can replace it with a 4 pin GM module once you figure out the polarity of the wires and remove the in line resistors which are not needed with the HEI module. THe vette mag pulse distributor will fire the HEI module just fine.
There is/was also an Accel distributor that is a small cap style, that triggers an HEI module mounted in or on it and fires a remote mounted coil. Good for using HEI on limited space manifolds. The late John Lingenfelter used such a distributor along with an I-6 cyliner HEI remote coil on hs A dragster for many years. He felt cheap good OEM stuff workd as good if not better than the tricked up race stuff. Such a system would surley serve adequately for most street stuff and do so with less cost and surely more durability.
The Germanium's were selectively sourced by GM in the day so that they worked as part of an integrated system. If you used generic replacements, you might not get the same advance curve as a factory spec'd amp might give.
Reason; They were using that germaniums transisistors to have spark fold back at high RPM. Drag racers do this via dual points where they retard ignition once they get into high gear for more power. GM was doing this by having the select fit germaniums switch slower as you went higher in the rpm range and in doing so, wah lah, spark retard without mechanical intervention..
Result was you got almost a linear spark retard as you got above 6000 rpm.
The "zero crossing" detector is also sort of unique in the circuit as this makes up for not having a bipolar supply. The zero crossing enables you to trigger on the RISE of the AC voltage that the pole piece/weight assembley signal gives to the box.
If you look hard and not too hard at that, you can take an early 4 pin HEI module and replace the guts of the Mag Pulse amp with it. IN fact, the GM circuit is exactly the same one used by Sunnen on theri now long gone distributor testors to take the distributor signal and fire the coil.
THe in line harness resistors simply limited current in case some idiot left the ignition switch on and the engine was not running.
Yes, the special mag pulse coil had a special turns ratio and it pulled lots of current. SOmthing like 8-9 amps. Some racers run them without alternators but that will limit the output voltage to the plugs. If you have a fried Mag pulse amp board, you can replace it with a 4 pin GM module once you figure out the polarity of the wires and remove the in line resistors which are not needed with the HEI module. THe vette mag pulse distributor will fire the HEI module just fine.
There is/was also an Accel distributor that is a small cap style, that triggers an HEI module mounted in or on it and fires a remote mounted coil. Good for using HEI on limited space manifolds. The late John Lingenfelter used such a distributor along with an I-6 cyliner HEI remote coil on hs A dragster for many years. He felt cheap good OEM stuff workd as good if not better than the tricked up race stuff. Such a system would surley serve adequately for most street stuff and do so with less cost and surely more durability.
