Quote:
Originally Posted by Argus25
I have never been sure how the manufacturer did the test for the Ft and just accepted the published value.Obviously in a grounded emitter circuit (from the AC perspective) the source impedance at the base will have a significant effect on the high frequency performance, the lower the impedance the better.
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They would use something like a General Radio 1607A Transfer Function and Immitance Bridge, introduced in 1958. This could be fitted with one of several transistor adaptors for grounded base and grounded emitter. Worked from 25MHz to 1.5GHz. Needs practice to use this beast.
http://www.ietlabs.com/pdf/Manuals/G...20Function.pdf
Or a Boonton 250A or HP250B with transistor test adaptors for 9MHz to 250MHz. Similar vintage to the GR
http://bee.mif.pg.gda.pl/ciasteczkow...onton/250a.pdf
http://www.jamminpower.com/PDF/HP/HP%20250B.pdf
Also described here
http://hpmemoryproject.org/wa_pages/wall_a_page_14.htm
For lower fT, simpler test jigs were appropriate - some of the Ge transistors were lucky to get to 1MHz.
Craig