Re: Why positive ground?

Posted by txblu....Dell(WA) knows on November 03, 2004 at 05:48:57 from (199.46.199.230):

In Reply to: Why positive ground? posted by Rosy on November 02, 2004 at 17:36:25:

Has to do with metallic migration due to electrons leaving one point and being collected on another. Positive grounds gave less wear and tear on breaking contacts, spark plug terminals.

Neg ground came about with the transistor radio (for automobiles) and 12 volts in the '50's and inparticular the Germanium transistor they used for the output device. These were PNP doped devices requiring a negative power source for the collector as it was P (+) material and needed to be reverse biased by a (-) power supply.

Since this was a 5 watt device (really large power dissipation for the early days of solid state) they wanted to make sure it was heat sunk good.

Apparently they hadn't perfected good insulators with good thermal transfer characteristics, so they decided to hard mount the transistor to the heat sink chassis. The heat sink was a large finned hootus and was attached to the radio's chassis which was attached to the dash metal, which was attached to the auto's body, then frame.

And (according to Dell.....as I recall) that folks,.......is the rest of the story (Paul Harvey).

Mark

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