02-02-2017, 05:22 PM
That mention of holes brought back a memory.
In 1965, Bush released their first hybrid TV, the TV135. We also had a visit from a Rank Bush Murphy field engineer that year.
He said that some of the older engineers (I was but a youngster then!) were having difficulty understanding these new-fangled transistors.
Valves, he said, are easy to understand. The cathode emits electrons, which exist. Now these electrons are attracted to the anode. Simple.
A transistor, on the other hand has holes but these holes don't really exist. Now these holes, they move ...!
As Lawrence said, you can recognise germanium and silicon types by the voltage drop across the base/emitter junction - provided, of course, that it is forward biased. In some small signal applications the voltage for a germanium type can be even lower than the figures Lawrence quoted, down to around 150mV.
If you have a data sheet showing voltages you should be able to use that information to deduce the transistor types without even touching the set!
There are two flavours of transistor that you should be aware of: PNP and NPN types. As a generalisation, most germanium transistors are PNP and most silicon transistors are NPN - but notice that I said most - not all! Silicon transistors have by far the greater numbers of PNP types mixed in with the NPNs.
The collector circuits of PNP types are fed from the negative supply rail with the emitter circuit being returned to the positive supply and if you see the positive supply rail is connected to the chassis, that is a sure sign that most, if not all of the transistors are PNP.
NPN types are more like valves in their powering arrangements - collector positive, emitter negative.
In 1965, Bush released their first hybrid TV, the TV135. We also had a visit from a Rank Bush Murphy field engineer that year.
He said that some of the older engineers (I was but a youngster then!) were having difficulty understanding these new-fangled transistors.
Valves, he said, are easy to understand. The cathode emits electrons, which exist. Now these electrons are attracted to the anode. Simple.
A transistor, on the other hand has holes but these holes don't really exist. Now these holes, they move ...!
As Lawrence said, you can recognise germanium and silicon types by the voltage drop across the base/emitter junction - provided, of course, that it is forward biased. In some small signal applications the voltage for a germanium type can be even lower than the figures Lawrence quoted, down to around 150mV.
If you have a data sheet showing voltages you should be able to use that information to deduce the transistor types without even touching the set!
There are two flavours of transistor that you should be aware of: PNP and NPN types. As a generalisation, most germanium transistors are PNP and most silicon transistors are NPN - but notice that I said most - not all! Silicon transistors have by far the greater numbers of PNP types mixed in with the NPNs.
The collector circuits of PNP types are fed from the negative supply rail with the emitter circuit being returned to the positive supply and if you see the positive supply rail is connected to the chassis, that is a sure sign that most, if not all of the transistors are PNP.
NPN types are more like valves in their powering arrangements - collector positive, emitter negative.
