Tim Williams wrote:
"John Popelish" wrote:

This reminds me of the vertical amplifiers in my old
Heathkit 5MHz scope. I perked up the high voltage stage by
cascoding those high voltage transistors. I tied their
bases to the +8 volt supply rail (+9 in this case) and added
faster, low voltage transistors in series with their
emitters. This gives the output stage something like a
pentode effect.

Yeah, I'm thinking of modding my IO-103, actually.

I suspect this circuit draws wee too much current for its supply though.
Suppose I could always add another transformer...

What kind of bandwidth did you get with the cascode?

I didn't even own a signal generator when I did this (poor
college student with 2 kids), but I was able to greatly
reduce a couple capacitor frequency boost networks between
pairs of emitters and still have a nice square wave response
with less ringing and squarer corners. I think I built a 1
MHz multivibrator as a test signal. The scope had a 60 Hz
voltage reference waveform generator that I used to get the
low frequency response back to where it started.