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?

Tim

--
Deep Fryer: A very philosophical monk.
Website @ http://webpages.charter.net/dawill/tmoranwms

"John Popelish" wrote in message
. ..
Tim Williams wrote:
I think I've got the key bits in there... like the common mode feedback
the
right way around.

It's a diff amp, but most scopes have a SE front end. So, like most
scopes,
the position knob goes to -in and signal to +in. A preamp might be a
good
idea for the more sensitive ranges.

The 2N5179 pair should be fast enough that I get the ~20 gain I want up
to
50MHz or so. '3904's are kind of pokey for this, but as emitter
followers,
who cares. That just leaves the hope that the C1569's are as fast as
claimed.

And if not, I could replace the *******s with a 6CL6. That'll show 'em.

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.