All Things Microsoft > Microsoft Software
Muzzy, why does Windows rule?
jtpenrod:
Do you know what? I've never really thought about it, I just acepted that valves are more linear than transistors.
That is perfectly true: valves are more linear than transistors. However, all too many folks latch onto that one fact and forget all about that output transformer. Linear valve + Nonlinear transformer= Nonlinear output. Valves also are low gain devices, so that there is insufficient open loop gain to linearize the transformer with inverse feedback. So a whole folklore grows up around these misconceptions, the marketing guys get hold of that, and the hype is lapped up like antifreeze at a petting zoo.
--- Quote ---
A little learning is a dang'rous thing; Drink deep, or taste not the Pierian spring: There shallow draughts intoxicate the brain, And drinking largely sobers us again.
-- Alexander Pope (1688-1744)
--- End quote ---
Nonlinear BJT + Inverse feedback + No output transformer= Linear output. It's really that simple.
Having said that nothing beats traveling wave tubes, klystrons and magnetrons in low noise high powered VHF and microwave amplifier and oscilator applications.
True: that's where "hollow state" beats solid state: RF applications.
piratePenguin:
I think it's time to get back on topic.
Windows is shit.
Aloone_Jonez:
--- Quote from: jtpenrod ---Do you know what? I've never really thought about it, I just acepted that valves are more linear than transistors.
That is perfectly true: valves are more linear than transistors. However, all too many folks latch onto that one fact and forget all about that output transformer. Linear valve + Nonlinear transformer= Nonlinear output. Valves also are low gain devices, so that there is insufficient open loop gain to linearize the transformer with inverse feedback. So a whole folklore grows up around these misconceptions, the marketing guys get hold of that, and the hype is lapped up like antifreeze at a petting zoo.
--- End quote ---
It's ok I understand I meant valve amplifiers in general, Valves alone are very linear, like you said it's lack of negative feedback due to their low gain and the output transformer being very non-linear that generally increases the distortion of valve amplifiers. Modern solid state amplifiers have a very high open gain despite the transistors are less linear than valves, the negitive feedback caused by the high open loop gain reduces the distortion, and there's no output transformer to mess things up.
I'm sure a class B valve amplifier (correct me if I'm wrong but valves lack crosover distortion so class AB isn't required) driving a high impedance loudspeaker for a load will have very low distortion, but it'd be bloody expensive and I bet you a cheaper modern solid state design could achieve similar performance.
--- Quote from: jtpenrod ---Nonlinear BJT + Inverse feedback + No output transformer= Linear output. It's really that simple.
--- End quote ---
In fact the bigest non-linear element in modern audio systems is the loud speaker system, but these have improved a lot too.
--- Quote from: jtpenrod ---Having said that nothing beats traveling wave tubes, klystrons and magnetrons in low noise high powered VHF and microwave amplifier and oscilator applications.
True: that's where "hollow state" beats solid state: RF applications.
--- End quote ---
I'd like to get my hands on some of these devices one day. :D
jtpenrod:
I'm sure a class B valve amplifier (correct me if I'm wrong but valves lack crosover distortion so class AB isn't required) driving a high impedance loudspeaker for a load will have very low distortion, but it'd be bloody expensive and I bet you a cheaper modern solid state design could achieve similar performance.
That's another unfortunate misconception. All active amplifiers show considerable nonlinearity at low currents, so all Class B amps have crossover distortion. They did try high impedance speakers in the late 1930s, however, I don't know what ever became of that.
Aloone_Jonez:
As I'm only 23 I've only covered transistor and op-amp amplifers in the courses I've taken so far - apart from RF vacuum tubes are considered to be obsolete. I've obviously also picked up many myths about valves and valve amplifiers in general.
Is there anywhere I can read about valves and valve amplifiers that will debunk the most common myths?
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