[Trevor Wilson[_2_]]

"Eeyore" wrote in message
...


Trevor Wilson wrote:

"Arny Krueger" wrote


For one thing, modern output transistors have Ft up in the megahertz
range. Back in the 70s people were still struggling with output devices
with Ft in the KHz range.

**Nope. The Japanese had a goodly number of complementary devices, with
decent Voltage, current and SOA ratings which extended well into the tens
of
MHz. By 1974, Hi-Rel had true Triple Diffused, TO3 devices with a 20MHz
fT
and 20 Amps capacity.

Hi-Rel ?

**Yep, Hi-Rel. They were a small manufacturer back then. A mate discovered
them and used their devices for his amplifiers. Very impressive devices. I
have a spec sheet somewhere. When I locate it, I will scan and post, if you
like. Purely historical, of course. The devices have been unavailable for
quite awhile. FWIW, the numbers a ED203 and EB203.



Exceptionally linear and very potent devices. I recall
them vividly, since Motorola had announced their intention to commit to
Epitaxial Base devices (ca. 2MHz), since it was impossible to produce
Triple
Diffused devices (according to Motorola). Other manufacturers also had
some
impressive devices back then. The Marantz 2325 receiver used
2SA747/2SC1116
devices. These posessed an fT of 15MHz.

I recall being impressed by Sanken devices the first time I was designing
a
serious amplifier around 1980. I settled for Hitachi lateral mosfets
instead.
Obtainability was a serious issue back then.

**By 1980, Japanese transistors were much more easily available. The 2SD555
and it's complement were my favourites at the time.



Having said all that, good gain linearity over a wide current range has
only
been a relatively recent development.

With modern low-Z driver stages, current gain linearity is no longer an
issue
the way it was.

**True enough, but, as you may recall, I have a preference for zero Global
NFB amplifiers. Every bit of linearity is helpful.

Trevor Wilson