[Eeyore]

"Michael A. Terrell" wrote:

Eeyore wrote:
John Larkin wrote:

True, none of this is relevant for audio. Anything will work for
audio.

Almost anything. RCA's 2N3055s weren't exactly the fastest in the world. 800kHz
fT IIRC. I hate to think what their germanium predecessors like the OC35 were
like.

The 3055 was developed for linear power supplies, so it didn't need a
high fT.

True enough, except Motorola's were faster anyway. Using the wrong brand in hobby
kits caused many a burnt out output stage.

Eventually I think the slower parts got an H suffix as in RCA's 'hometaxial' process.



It was scaled down from the RCA 40411, which was a 100 volt
device, VS a 60 volt, cheaper device. The 40411 was used in some audio
amps in some early RCA semiconductor data books. In fact, the 60 watt
amplifier used the 40406, 40407, 40408, 40409, 40410, and a pair of
40411 transistors, and a couple diodes to sense the temperature of the
heatsinks. I built a PA amp from that sample design in the late '60s.
It, and a preamp were also built on my first hand made PC boards.

I know the very one and still have that handbook. I built one too. The little
heatsinks welded onto the drivers were an intriguing novelty that never caught on.

In the UK, WEM 100W PA and instrument amps were based on that design for years. They
got 100W by using 6 ohm speakers !

Graham