"John Larkin" wrote in message
...
The other trick is to add peaking inductors.
Yeah, reminds me, I took apart a bunch of monitors -- that's where I got my
BFQ221, 241, 225's and PH2369's from -- which used 1.3kohm 5W collector
resistors, and a little bit of inductance. I forget what it was, 10uH or
something. Dang, just the other day I took down the last board that I had
left up here. Ah well, it would do something like that in any case.
The simplest is to add an
inductor in series with the final 1K collector loads. The ballpark
value is
L = K * R^2 * C
Alright.
where C is the net capacitance (transistor + deflection plate +
wiring)
I'm going to guess in the ballpark of 10-50pF. How much capacitance does
300 ohm twin lead have, and what's a typical capacitance to chassis? Hmm, I
was going to look for a datasheet on the CRT, too. That would give me
deflection plate C.
Next step is another inductor, in series with the outputs. Another 20%
maybe. Finally, an optimun t-coil can increase bandwidth by 2.8x over
no peaking at all.
So series resonant with the deflection capacitance?
Please explain "t-coil".
As JP mentions, it helps to cascode the output stage, which reduces
feedback (Miller) C
Yeah, that was something else I was going to do- didn't draw it. Speaking
of things to do, is there any advantage to using collector or emitter drive?
Above, I show the outputs driven by an emitter follower. The original HK
schematic shows PNP collectors. Given the same bias current, slew rate is
about the same, so would I be better off going for the collector voltage
gain?
and allows you to use something really fast on the
bottom, like a gaasfet or a phemt maybe.
Hey, how about a fast opamp driving a phemt-C1569 cascode, with
peaking inductors?
I want to see waveforms /on the CRT/, not by the electromagnetic energy the
driver circuit is radiating! ;-)
Speaking of fast-assed parts, I'm going to need to get myself some snap
diodes some day. Got a supplier, or some extras?
Tim
--
Deep Fryer: A very philosophical monk.
Website @
http://webpages.charter.net/dawill/tmoranwms