Fets for the MigFet

[comradehoser]

Given the extremely specific information on the 5457 specs in the Migfet build docs, I used my little box of Chinese Magic, the LCR-TC-1 Multi-function tester and no fewer than 11 through-hole 5457s. It gives the report as

IDSS
Id
@Vg
Id
@Vg

It's not super clear to me what these mean, I assume one is Vg on and the other Vg off. @owlexifry stated that he tried to find jfets with Vgss of 3 ma and Vp of 1.5v.

Closest I come is idss of 2.3, 2.0, then 1.8 ma. No idea what Vp corresponds to, but the only TC-1 measure I have in that range is the second @Vg figure, ranging from 1.58v to 1.32 v.

Build docs reference idss of 2.23, .90 and .87. Lowest I've got is 1.1.

Not sure what I should be aiming for--as high as I can for Q1 and then as low as I can, or.... (?)

 

[owlexifry]

bear in mind, the testing methods are different.
i used this vero circuit:

(could be breadboarded instead)

just found my notes. looks like i grabbed a handful of 11, measured as per above method, and just picked x3 with the highest Idss.


tbh i wasn’t really able to comprehend the JFET selection requirements as specified on the build doc, so idk, whatever i did worked and it sounds great