15-04-2015, 04:03 PM
(14-04-2015, 08:18 AM)Old Sparky Wrote: IIRC, there was no standard colour coding for transistor lead-out wires, and different manufacturers used different colour sleeves to denote collector, base & emitters. OC170, AF117, etc have their lead-outs in this form 'e,b,s, c' (i.e. the gap between the screen and collector is bigger than that between any of the other leads, whereas OC71, 81, etc., and some of the AC127 types have a coloured spot on the metal case to indicate which lead is the emitter. Data Books, such as those published for many years by Mullard and Towers are very helpful in identifying transistors, providing details of pin-outs, Hfe, Ic., and other parameters. Entering a type no. into a search engine will also produce on-line data sheets for many devices. (Apologies if I'm stating the obvious here!) As to misleading readings when checking transistors in situ, this is usually due to resistors or inductors being connected, not always in an obvious way, in parallel to semisonductor junctions. It's easy to assume that a transistor or other device is faulty,, when the problem is in the associated circuit. I've done so myself, including a couple of times recently, and I've been working with electronics for about 44 years!
From a superficial glance, it seems most very early transistors were bunged in with the base pretty much bang in the middle. I assume that is mostly the case. I have a 1959 Bush and I always tend to get one way readings between green centre wire and the two external leads. So, I assume the middle one is the base.
Anyway, I'm now just going to try my best, change the capacitors, check the waveband and ferrite rod and see if it can be done.
Any tips welcome.
