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October 03, 2025, 04:06:57 PM

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Too much base ?

Started by saturated, September 27, 2025, 02:01:08 AM

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saturated

I wanted to set up a circuit and see what happens.

Previously I was trying to do something different and after gathering a few components my calculations showed a voltage drop across the collector resistor of 23.9 when Vcc was 24 volts  :grr

So today I wanted to put together a circuit with a lower base resistor and see 🙈 if it would melt or blow up the transistor I had no idea what it would do.

Here is the schematic

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So I put it together and dialed up the voltage and kept watching for smoke but really nothing bad happened (I don't think)  :loco

Also I measured emitter current

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And here are my results

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One thing I am noticing is the lower beta value seems iirc in all the book experiments i did beta was about 170  xP

Seems like the base emitter voltage drop looks good so maybe I was nowhere near Chernobyl territory idk and that wasn't what I was trying to do.  I tried to feel if the transistor was getting warm/hot but it's tiny and I couldn't really tell.

My main interest was with the suspected huge voltage drop across the collector how much was gonna be left for the emitter resistor  :grr


I ask stupid questions
and make stupid mistakes

criticism, critique, derision, flaming, verbal abuse welcome

J M Fahey

The classic "universal" values for these ultra simple gain stages is:

3k3 to 4k7 load resistor with 1M Base>Collector.  NOT Base>+V as you show.
or
10k load resistor with 3M3 Base>Collector.

The beauty is that it is self-adjusting so it works with almost any transistor, no need for careful selection or trimming.

Try it and post results.

You will see Collector self biases *near* V/2 which is what we want.

Back in the day (in the 80s) I designed and published a series of Magazine articles showing how to DIY a ton of projects, from a single transistor Guitar booster to 6-12 channel mixers.

Many still in use today, 40 years later!!!!


galaxiex

Hey JM are any of those articles/projects around anywhere online?  <3)
If it ain't broke I'll fix it until it is.