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.

--Tom

--
Prof. Thomas H. Lee
Allen Ctr., Rm. 205
350 Jane Stanford Way
Stanford University
Stanford, CA 94305-4070
http://www-smirc.stanford.edu

On 11/16/2020 06:35, charlesterrebonne@hotmail.com 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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