Re: Q122/222 Jfet J300 subs for 2215A scope ?

Tom Lee

Instead of sticking in a socket, just measure IDSS first. I posted the current range that will work.

You may still have a problem with the bias circuit. I've never run into a 22xx scope that was anywhere near as fussy about FETs as yours. That bias circuit is quite forgiving.


Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070

On 11/16/2020 06:35, wrote:
thanks to all who replied - the 2215A scope is off the bench for now but Ill get back to it soon and will report when I get this working...I am almost at the point of sticking a high quality transistor socket there and just trying some other close to J300 specs Jfets I have on hand...FYI all the parts I have tried in the Q122/Q222 position in the scope : 2N3918, NTE133, k19, NTE132 tested good out of circuit...i have some more Jfet #s in my stock I need to try.

From the Tektronix replaceable parts reg. : 151-1124-00 = Siliconix J-2400...would'nt be surprised this was not a custom design but more likely tested/hand picked J300s jfets and assigned a Tektronix custom part# from Siliconix...searching Siliconix j-2400 brings up nothing...Id suspect most input boards from that 22xx series scopes came off the assembly line with "J300" marked Jfets in those Q122/222 positions..thanks

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