R
Rich Grise
- Jan 1, 1970
- 0
Hello Rich,
Because that one was for ham radio and the stuff for secondary user UHF
needs FCC blessing.
Ah.
Thanks,
Rich
Hello Rich,
Because that one was for ham radio and the stuff for secondary user UHF
needs FCC blessing.
Kevin Aylward wrote:
A bi polar transistor is a current controlled device actually.
A small base current is used to control a larger collector current.
A FET is a voltage controlled device.
Indeed. It is they way they work. Only the illinformed consider that the
transister is current controlled.
What we have here is an enormous amount of erroneous waffle on the
bipolar transistor. Its quite amazing really. There is no point in
perpetuating this daft myth. It only leads to confusion.
Any *actual* *understanding* of the standard 3 junction pictorial
descriptions of basic transistor operation should leave people with no
doubt as to the correct operation of a bipolar transistor. Base current
don't "cause" the flow of collector/emitter current.
My inclination is to a multiple-microphone version for later
expansion, since they do a lot of Flag Ceremonies with multiple
speaking parts.
John said:No, being 'informed' doesn't make an engineer pick a more difficult
analytical approach to quantitative circuit design; quite the
opposite.
90% of the time, a simple 0.6Vbe-plus-Beta model is the
easiest and *most reliable* way to design transistor circuits.
This is sci.electronics.design, not sci.device.physics. If I had to
analyze the physics of every component I use, I wouldn't get anything
done. What matters is how they behave.
That's like saying that poison doesn't cause death because only heart
failure *really* causes death.
Roger said:Most of us know how to design a simple bipolar transistor stage using
the current model.
The design equations and explanations need just a few rows of text.
How would you design the same transistor stage using the
voltage-controlled model?
http://www.anasoft.co.uk/EE/bipolardesign1/bipolardesign1.html
Can you show us how your way is faster, better, etc..?
How does it work in real transistor stage design?
The voltage controlled model is the simple model, and the correct one.
Not at all. This is not true in the slightest.
Please explain, as discussed in this thread, from a beta perspective,
why a hfe mismatch of 2 can result in say, 10 times mismatch in current
(or more) for || devices. Why is it not just a factor of 2?
Its not about the physics is about understanding how to design
transistor circuits correctly. To do this, one must understand that the
transistor is a voltage controlled device. The why is irrelevant. Sure,
for a simply switch one might just work out the base current needed to
saturate the device, but for any design that isnt trivial, the beta
model is, essentially, useless. The first order model for gain doesn't
even have a beta term.
This is really all getting a bit tiresome. I have explained this many
times. Base current is an effect caused by an application of voltage.
Without understanding this basic fact, it is impossible to *design* an
amplifier correctly. All one can do is piss about under the illusion
that there was a "design" performed. Period.
John said:Then I owe somebody about $200 million.
Because the beta model doesn't address current sharing of base
currents when transistors are paralleled. Discrete circuit designers
rarely (as in, never) hard-parallel bipolar transistors anyhow.
If
they ever elected to do so, they would have to analyze the situation
properly.
Nobody can afford to design without regard to min/max beta specs. Not
even you.
Well, maybe yours doesn't, but that's just the equations you prefer,
to make your point.
So, if A causes B, and B causes C, you conclude that A does *not*
cause C. OK, can't argue any more about that.
That is one reason why we changed to NiMH. The other was cost
as 9V alkalines are really expensive. They rarely go on sale like AA
batteries sometimes do.
The theatre technicians here in London UK seem to be able to source
alkaline 9v batteries at about a third of the retail price of a
Duracell.
Joerg said:Hello Laurence,
That would be 30c US. Really?
Regards, Joerg
Also, try to develop a connection with local hospitals and clinics. A
friend of mine used to get cases of alkalines (9V, AA, whatever) free.
Apparently, for medical use, they must be discarded by law when they meet
the expiry date. They were still good as new.
Joerg said:That's right, except that 9V are a lot more expensive per Watt hour than
AA batteries. But the real concern I have with 9V is that even brand new
ones fail a lot. Happened again this week at church. After just a few
minutes a brand new battery went from 9V to zero. They are just too
fickle.
Agree. At the same gig where we've gone through literally tens of thousands
of AAs in wireless mics with not a single problem, we've had probably a 1%
failure rate in 9V batteries for the few wireless units we have that take
those. Same thing as what you describe - they test okay, and then drain
within minutes.
I assume it's because of the multi-cell internal construction of a 9V.
Anno Siegel said:Perhaps because Tom Lehrer's text is different:
There is no practical example on that web page, and it surely does not
look like a simpler or faster way to design a transistor stage.
About time to start a new thread ?
It all depends. Depends on your budget and the quality you're looking for.
I'm guessing that budget is low in your case. You *can* get cheap 'voice quality'
radio mics but these aren't a patch on the Sennheisers that Joerg is using.
You get what you pay for for the most part. The receiver should have no trouble
interfacing with any kind of PA gear btw.
I'm tempted to suggest looking on ebay for a cheap unit.
I remember reading years ago that the spoken human voice could be
intelligible at a quite high distortion level. I think the amplifier
in question was 30% or somesuch, but that sounds high even to me now.
Depending on the venue, even room acoustics may outweigh any
distortion issues, I'd guess. Think of the US National Anthem sung at
a sports venue...
"for th or e la and e nd of...you get my drift.
Tom