ll be built from random electronic scrap. There's a darlington pair class A stage where I need to know the minimum hfe we can count on with 95% confid ence. The darlington pair consists of a small random npn followed by a 2nd tr that must dissipate 1w in hot weather with a small crude heatsink. We ca n eliminate high voltage trs from the picture.
il as it can. Peak tr current is anything upto 1A.
uggling to answer that question.
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IME its the high voltage ones that get that grim on hfe - does the same pro blem apply to some low v ones too? We can eliminate hi v power trs from thi s. Probably.
Use AC bias. It is only audio, so just make a 30 kHz oscillator and bias it ike they used to bias tape. this removes alot of vaiables, and if you give it just a little bit of inductance on the output lik=ne, will be very forgiving on devoce parameters.
Think soft.
Oh, and if Thinksoft hasn't been used for a name yet and you use it you better take care of me or I am comning over there with my gun....
it like they used to bias magnetic tape. This moots alot of vaiables, and i f you give it just a little bit of inductance on the output line, will be v ery forgiving on devce parameter variations. Think soft. Oh, and if Thinkso ft hasn't been used for a name yet and you use it you better take care of m e or I am coming over there with my gun.... LOL
Its Avlinux 6.0.1, debian based. But its faulty somehow, won't run anything I install.
Yesterday I tried to get PC no2 running it, but other problems there. Currently working on an old laptop that's sat unused for years, hopefully that will do it.
OK fixed an ancient laptop running 98 and got LTspice on it. Will post the schematic when its finished. Trouble is, the thing won't sim! It goes thru its calculations for however long, but doesn't plot anything on the graph, its just a black black area with axes. :/ What is it with computers!
be built from random electronic scrap. There's a darlington pair class A s tage where I need to know the minimum hfe we can count on with 95% confiden ce. The darlington pair consists of a small random npn followed by a 2nd tr that must dissipate 1w in hot weather with a small crude heatsink. We can eliminate high voltage trs from the picture.
Spice reckons it works nicely. Quiescent output voltage (bottom of loudspea ker) is 2.8v, which will drop a bit as tr2 gets hot.
Just one thing I'm not following. Spice says it has a V gain of over 6 - I' d expect far less given R1&2. Why so much gain?
Maybe I can answer the question. The signal source is much lower impedance than the feedback/bias resistors, so it rules. It would explain the visible nonlinearity. Adding 47R in series with signal input gives better linearit y.
Much thanks to everyone for raising potential issues. I'll build it IRL whe n I can, check it works sufficiently well in the real world.
There's nothing but scrap. Maybe one could built a meter using LEDs but why make life hard if its not needed? Time is not in generous supply, people work long hours for food.
ias it ike they used to bias tape. this removes alot of vaiables, and if yo u give it just a little bit of inductance on the output lik=ne, will be v ery forgiving on devoce parameters.
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