transistor pinout question,..

With rare exceptions devices are shown from the bottom and numbering is clockwise.

This is a carryover from the days of vacuum tubes. Most early tubes had larger pins for the heater or filament. That made sure that it took a determined idiot to plug the tubes into their sockets incorrectly. When octal and loctal base tubes were put on the market, they had keys that guided them into their socket in the correct orientation.

The tab on the transistor corresponds to the key on the tube. Numbering was always as seen from the bottom because that was the direction you looked in when soldering onto the socket.

Bill

-- Fermez le Bush

Yes. IIRC, only some antique Philips tubes were numbered in reverse.

Going back to the 1960's, Mullard, for one, used a Red dot to signify the Collector. There was also a lead spacing difference but it was very small and not easily seen. This dot was used on all round can (both glass and aluminium) transistors of the OCXXX series. The OCP71 phototransistor used a white line instead of the dot to signify the sensitive area and most also had the dot as well.

Once the transistor bodies were moulded it became easy to have a moulded face or edge to do the same thing.

My stepfather worked at Mullard for 40+ years and I remember going to the New Road factory in Mitcham for his 25 years dinner in the early 1960's, and being shown round the valve production lines and then the transistor lines. They made the OC4X and OC7X series at Mitcham.

All the transistors were tested by hand and sorted by characteristics, piles of these 'new' things on the benches all being hand sorted by women with appropriate test equipment.

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web:

And the 'tab', most commonly signifies the emitter. On all the common 'TO', pinouts, like TO18, this is used.

Best Wishes

You weren't in Crawley, Sussex in the 1960's were you?

Peter

-- Peter & Rita Forbes Email: snipped-for-privacy@easynet.co.uk Web: