Re: Hameg HM307-3 Cleaning and Repair
Hameg 307. input FET TIS69.
This is a low Idss N channel FET which is supplied as a pair matched to 10mv Vds and 10% Idss current. Texas 1971/2.
BFS21 is a Philips matched pair, very similar.
Otherwise use a couple of low current FETs and select in circuit for similar Idss and Vp. I have used 2N5245 and BFW12. Also try BF245, BF256A, BFW61, 2N3822, though you may need a wider range to make your selection.
As a manufacturer, it is cheaper to use tightly specified components and pay the extra purchase cost than have to select or adjust on the workbench. But for us just repairing one machine, a bit of adjustment is really the simplest, and vastly cheaper. I have found that I can get two pairs to match well from a selection of 5 or 6 from the same batch.
wme_bill
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