Re: Transistor selection (ii)

Tim Williams tmoranwms@xxxxxxxxxxx posted to sci.electronics.design:

Digging through my parts box, I found exactly four 2SC1569's, which
probably
came from old TV video outputs. Why it isn't three or six, I don't
know... http://harmsy.freeuk.com/nic.percival/2sc/2sc150.html
300V, 0.15A, 12.5W (awfully low for a TO-220), 40 hFE, 100 fT.

These sort of transistors seem to be hard to come by. Just what do
they use
for oscilloscope deflection, anyway?

Along the way the changes in o'scope CRT deflection went from simple
parallel plates to distributed deflection. This added quite a bit to
the capacitance but improved the deflection sensitivity from many
(tens of) volts per inch to (many tens of) millivolts per inch. This
reduced the required magnitude of deflection voltage to fast
transistor range. Trying to speed up a HV deflection amplifier
without resorting to ultrafast HV FET's may be impractical.

Er well, used to, anyway. I
suppose they're almost all digital and sampled stuff *these* days...
but back in the old days they needed *something* good for hundreds
of MHz bandwidth and
hundreds of volts deflection. I can imagine pentodes doing that, or
even a distributed amp, but there's only one tube in my Tek 475.

Speaking of HF transistors, would you happen to have SRF397 in your
records
anywhere? Also, PT4576 or PT4578, CA2206, SS4556, etc. I've pulled
a bunch of RF types that don't seem to show up anywhere.

Tim

P.S. I'm thinking of modding my Heathkit IO-103. I'm thinking
either improve what's there (not much to say for it, as is..), rip
it out for a bare X-Y display (raw CRT leads ran to the front panel,
or with deflection
amps of some bandwidth), or maybe try making a whole sampling
'scope. I must say it would be impressive to hike bandwidth from
10MHz to 1GHz.

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

"Winfield Hill" <hill@xxxxxxxxxxx> wrote in message
news:1188770819.218850.326920@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
On Sep 1, 10:18 pm, "Tim Williams" <tmoran...@xxxxxxxxxxx> wrote:
So for example, say I wanted a transistor:
Vcbo >=200V
Ic 0.1-2
Pc >= 10W
fT >= 100MHz
How would I go about that?

*Wading* through Digikey's stock, I found a 2SC5993 that's almost
there
(180V). Onsemi has a nice parametric search, but nothing in the
range.
I
tried going to Fairchild's website, but their search sucks (and
the
whole
website isp barely in English anyway). I've had better luck
skimming
over
Japanese transistor tables! Too bad anything in there is
probably unobtainium.

MCM is taking orders (for later delivery) for
"subs" for Sanyo's 2SC4188 (200V 10W 150MHz) and
for Toshiba's 2sc2238b (200V 25W 100MHz), and
2sc1569 (300V 12.5W 100MHz), and for Matsushita -
Panasonic's 2sc1819 (300V 15W 100MHz).

Toshiba's 2sc2238 (160V 25W 100MHz) is in stock.


.