Looking for a datasheet of a E421 J-FET. Searched high and low on the internet for this, can't find anything. Seems to be a very exclusive component. Found datasheet of U421, but specs seems an unlikely match.
Footnote: E321 is an obsolete matched N-Channel FET-pair, used as front-end differential amplifier in a Heathkit IO-4235 oscilloscope. This stage is prone to thermal drift. Trying the circuitry.
Footnote: E321 is an obsolete matched N-Channel FET-pair, used as front-end differential amplifier in a Heathkit IO-4235 oscilloscope. This stage is prone to thermal drift. Trying the circuitry.
