Active probe?

[Brenton7]

I have a Tektronix P6202A 500Mhz active probe that uses this exact circuit. However when I attempted to use it I discovered it was U/S. Must have been like this when I received years back. Tracked the problem down to the input FET chip. The half that connects to the -7 Volt was short. I have attempted to replace this chip with two MMBF4416LTI UHF Jfets but getting the bottom FET to conduct seems to be a problem. This fet was specified having a IDSS of 10mA but analysing the circuit seems in indicate higher current f around 15mA. the circuit uses + and - 7 volt supplies with only 27Ohm source resistors. Not sure whether the fet characteristics are vastly different or what the specs were for the original. Working on this front end in micro surgery with the SOT-23-3 devices making changes almost impossible.

Any ideas?

[haastyle]

This design works amazingly well:
https://jmw.name/projects/active-probe/

Files are here:
https://github.com/drandyhaas/oshw-active-probe

I've tested it extensively and it performs as advertised. Flat within 1 dB from DC to 2 GHz!

I plan to also sell them alongside the Haasoscope Pro 2 GHz open-source oscilloscope on CrowdSupply:
https://www.crowdsupply.com/andy-haas/haasoscope-pro

(I made a 3D printed case for it - looks much better now than on the webpage. )