Good that you recognize that as cascode. I've ran into techs all over the place who have no clue what that is and think you are making a mistake and mean cascade. (as of now I can tell you my spellcheck does not now WTF cascode is)

Anyway I had to pull the Tek off the bench for a bit to do a Luxman R-117. Healthy receiver really. Thought maybe it was BFC but it's 160 a channel and built for it. But I am back on it next time I go down there.

But anyway, that is pretty much the word - cascode. Used to get the maximum voltage gain.

Usually it has a very high output impedance but they way they got it the transistor is just pulsed I think. It is like Q 4565 is used as a comparator. It would have to be because it appears to feed the R/C network created by the time/div switch.

The more I work on Teks, the more I am impressed with their designing skill.. I have never seen anything like it, it is almost scary. Like now, I am going to look into whatever specs I can get on Q 4565 before I just stick something in there.

I got a 561A that was built before I was born and the technology in it is amazing. I got the good plugins for it too, dual time base and dual trace. And almost all tube. In fact I think it may predate tunnel diode triggering. I mean, it may predate tunnel diodes :-)

And mine has a very strong CRT with no screen burn at all.

Anyhow, I think the main thing I need in this transistor is high gain. Voltage and current requirements are minimal. Frequency response should not be much of a problem these days. Since all it does is pulse, even if the ft of the replacement is up in the gigahertz there should be no problem.

I'll keep y'all posted.

And thanks.