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WME_bill · 22nd Mar 2018, 7:08 pm

FET for D54.
Three leads are needed to make a FET work. Source, Drain and Gate. The 4th lead is substrate or screen.
On a TO72 metal case transistor, counting from the tag, comparable pins are emitter, collector, base, substrate-screen. If using the FET as a VHF amplifier, then the screen may be helpful.
For this particular use in the D54, no need for the screen. That is why the 4th lead is often cut off, as an alternative to finding somewhere to solder it to keep it from straying. The TO18 case is identical but with 3 leads only.

Many of these FET use the same chip, and the type number changes for the packaging, and sometime as a selection of closer characteristics.
The UC734, 2N4416, 2N3819, 2N3823, 2N5245, 2N5435, BF245, MPF102, J304 all use the same chip, in either TO72 (4 led metal), or TO18 (3 lead metal) or TO92 (3 lead plastic) package.
The TEK 151-1031 is 2N4416, and 151-1042 is one of a pair of 2N4416 matched for Idss within 0.5ma. 151-1070 is same but more closely matched.
Matching is to simplify set up in when manufacturing. Not important to us, as we can spend the extra 10 minutes setting up the preset controls individually. And temperature effects are not likely to worry us, unless you want to move it from -40C to +70C in an hour, and still expect readings to remain constant.

Incidentally, with most FET, the Source and Drain can be interchanged, so don't get worried if the pcb layout seems inverted.
wme_bill.

22nd Mar 2018, 7:08 pm	#18
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: Telequipment D54 ? FET for D54. Three leads are needed to make a FET work. Source, Drain and Gate. The 4th lead is substrate or screen. On a TO72 metal case transistor, counting from the tag, comparable pins are emitter, collector, base, substrate-screen. If using the FET as a VHF amplifier, then the screen may be helpful. For this particular use in the D54, no need for the screen. That is why the 4th lead is often cut off, as an alternative to finding somewhere to solder it to keep it from straying. The TO18 case is identical but with 3 leads only. Many of these FET use the same chip, and the type number changes for the packaging, and sometime as a selection of closer characteristics. The UC734, 2N4416, 2N3819, 2N3823, 2N5245, 2N5435, BF245, MPF102, J304 all use the same chip, in either TO72 (4 led metal), or TO18 (3 lead metal) or TO92 (3 lead plastic) package. The TEK 151-1031 is 2N4416, and 151-1042 is one of a pair of 2N4416 matched for Idss within 0.5ma. 151-1070 is same but more closely matched. Matching is to simplify set up in when manufacturing. Not important to us, as we can spend the extra 10 minutes setting up the preset controls individually. And temperature effects are not likely to worry us, unless you want to move it from -40C to +70C in an hour, and still expect readings to remain constant. Incidentally, with most FET, the Source and Drain can be interchanged, so don't get worried if the pcb layout seems inverted. wme_bill.