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WME_bill · 19th Mar 2018, 10:35 pm

Input FET in Scopes. Telequipment D54.
The FET used in the input stages of scopes are selected. The manufacturing process leaves wide variation in characteristics, so the FET manufacturers do some selection, varying also on packaging (TO18,TO92,TO72, 3 pin or 4 pin) to give a range of commercial type numbers.
Then the scope manufacturer specifies closer tolerance, and his supply is specially selected, at extra cost. Hence the strange numbers which no-one can recognise.

I have checked the characteristics of them in several Telequipment and Tek scopes and others.
In general, they appear to be low Vp (pinch off voltage) and moderate Idss (Zero bias gate current) eg Vp =1.5v. Idss = 3.5ma, with a wide variation. If you want something exact, try the makers.

I have seen in Telequipment scopes (some may be servicing substitutes):
151-1051=2BFW1051. dual clipped together for D54.
151-0242 = BFW0265 for S54
151-1052 = BFW1052 for DM63 & D67
151-1036 = SU2351, 2N4393, TFD1551 dual for DM63
151-1125 = SU2603K,SU2603M Dual DIL (different pinout, but board of D1010 accepts either), BFW1118 dual.
All as the input stage on the Y amplifier.
If you want something which works so that you can use the scope, then try commercial types such as:
BFW13, BFT46 (used frequently by Philips in their scopes, as ON471), 2N3823, 2N4117, BF245, BF256, 2N5246, 2N5457.
If dual, then you can use two with common clip holding them together, as BFS21, or make up your own clip.
wme_bill.

19th Mar 2018, 10:35 pm	#5
WME_bill Octode Join Date: Oct 2007 Location: Exeter, Devon, UK. Posts: 1,554	Re: Telequipment D54 ? Input FET in Scopes. Telequipment D54. The FET used in the input stages of scopes are selected. The manufacturing process leaves wide variation in characteristics, so the FET manufacturers do some selection, varying also on packaging (TO18,TO92,TO72, 3 pin or 4 pin) to give a range of commercial type numbers. Then the scope manufacturer specifies closer tolerance, and his supply is specially selected, at extra cost. Hence the strange numbers which no-one can recognise. I have checked the characteristics of them in several Telequipment and Tek scopes and others. In general, they appear to be low Vp (pinch off voltage) and moderate Idss (Zero bias gate current) eg Vp =1.5v. Idss = 3.5ma, with a wide variation. If you want something exact, try the makers. I have seen in Telequipment scopes (some may be servicing substitutes): 151-1051=2BFW1051. dual clipped together for D54. 151-0242 = BFW0265 for S54 151-1052 = BFW1052 for DM63 & D67 151-1036 = SU2351, 2N4393, TFD1551 dual for DM63 151-1125 = SU2603K,SU2603M Dual DIL (different pinout, but board of D1010 accepts either), BFW1118 dual. All as the input stage on the Y amplifier. If you want something which works so that you can use the scope, then try commercial types such as: BFW13, BFT46 (used frequently by Philips in their scopes, as ON471), 2N3823, 2N4117, BF245, BF256, 2N5246, 2N5457. If dual, then you can use two with common clip holding them together, as BFS21, or make up your own clip. wme_bill.