"Arny Krueger" wrote
"The biggest problem with the amps is poor current haring between the output triodes. All 4 need to be matched closely to
prevent failures. Initial matching on the bench ensures initial reliability."

A hearty DOOOH! to that!

**** me. It must be a **** design then.

Do you design a transistor circuit making assuptions about h_FE?


Martin
--
M.A.Poyser Tel.: 07967 110890
Manchester, U.K. http://www.fleetie.demon.co.uk

"Fleetie" wrote in message
...
"Arny Krueger" wrote
"The biggest problem with the amps is poor current haring between the
output triodes. All 4 need to be matched closely to prevent failures.
Initial matching on the bench ensures initial reliability."

A hearty DOOOH! to that!

**** me. It must be a **** design then.

Do you design a transistor circuit making assuptions about h_FE?

**Some do. Fortunately, BJTs offer very long term hFE stability, once
chosen. Valves, OTOH, vary all over the place, with time.


--
Trevor Wilson
www.rageaudio.com.au

In article , Fleetie
wrote:
"Arny Krueger" wrote
"The biggest problem with the amps is poor current haring between the
output triodes. All 4 need to be matched closely to prevent failures.
Initial matching on the bench ensures initial reliability."

A hearty DOOOH! to that!

**** me. It must be a **** design then.

Do you design a transistor circuit making assuptions about h_FE?

Yes. I assume it will vary over a range bigger than written in the
databook, and slug the value accordingly. :-)

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

"Fleetie" wrote in message

"Arny Krueger" wrote
"The biggest problem with the amps is poor current haring between
the output triodes. All 4 need to be matched closely to prevent
failures. Initial matching on the bench ensures initial
reliability." A hearty DOOOH! to that!

**** me. It must be a **** design then.

Do you design a transistor circuit making assuptions about h_FE?

Yeah, I presume that h_FE will be all over the map. While Trevor is right
about a given device sample having stable characteristics, that's only true
if the device is operating under tightly-controlled circumstances that are
unrealistic in the real world.

IOW h_FE varies with temperature, current, applied voltage...

And it varies from device to device.