#836

Episode 836
What are emitter resistors and capacitors? Why are they there and what to look for if things are not working right.
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[@joeteejoetee]

I think you made the best video demonstration ever of emitter biasing, and how the capacitor's conductance in AC effectively makes iit a common emitter amp. Kind job selecting the resistor values for common parts and math reasons too. I'm glad you limited the potential infinite scope of transistor biasing and NAILED IT with these 3 Videos with real-world parts and passive components! Bravo Sir!

[@IMSAIGuy]

Thank you very much!

[@xorfive]

I'm learning a lot from this channel. Please keep them coming!

[@jimmydburrell]

Love transistor circuits. Analog or “old school” as the kids say… it’s just so much more fun :)

[@pyrokinetikrlz]

Ohhhh so many fascinating details that can be told in a video series about "advanced topics on transistors" :D

[@frankowalker4662]

That's cleared up quite a lot, Thank you.

[@stevepence9869]

Would you do a video on ESR and why it is important in transistor circuit

[@geirendre]

Excellent video series. Is it safe to assume that a Cathode resistor (and capacitor) in a similar tube amplifier stage does the same things?

[@IMSAIGuy]

I don't know tube circuits

[@thomasdial8664]

Yes. Common cathode vacuum tube, common emitter transistor, and common source FET circuits are pretty similar in behavior, although circuit component values may be quite different.

[@paulcohen1555]

@@thomasdial8664 And in the tube circuit the cathode resistor also biases the tube.

[@thomasdial8664]

@@paulcohen1555As it also does in the other circuits. The current in the emitter/cathode/source path affects the base/grid/gate bias in similar ways. It would be interesting to see a demo of the same basic circuit with each of the three types of device (or four, counting enhancement and depletion mode FETs as distinct types), although the cathode heater circuit would make the tube demo a bit messy.

[@jdmccorful]

Would you be willing to advance to transistor substitution? Replace that transistor with a different transistor and get the same results. What to know when doing the change. Thanks for the look.

[@IMSAIGuy]

That would be super advanced and very difficult. Each use case is different to determine what is critical and what is not.

[@jdmccorful]

@@IMSAIGuy oh well, just hoping.

[@RexxSchneider]

The rule of thumb is that in any common emitter stage with an emitter resistor, if the smaller of the base bias resistors is not much bigger than the collector resistor, then the biasing does not depend significantly on the β of the transistor. So any small-signal transistor that can handle the supply voltage can be substituted with negligible change to the performance of the circuit.

[@paulcohen1555]

There is something that bothers me with the values of the input/output capacitors: They are 0.01μF in the schematic. With less than 1KΩ input resistance it gives an low cuttoff frequency of about 16KHz. The frequency of the signal as can be seen on the scope is about 1.4KHz. How it fits together? ("Where is the catch")?

[@IMSAIGuy]

gain

[@RideGasGas]

Is one of the channels inverted on the scope? The output wasn't inverted from the input. I noted some phase shift, but quite a bit different than 180 degrees. Just curious.

[@IMSAIGuy]

did you watch part I

[@RideGasGas]

@@IMSAIGuy I did. There the amplifier is inverting. Here at ~6:50 it doesn't look like it so much. I have a GW Instek scope so not familiar with the Rigol and couldn't see clearly if the second channel is inverted.

[@IMSAIGuy]

@@RideGasGas Oh, ok. Yes there is a phase shift due to the capacitors

[@IMSAIGuy]

here is a video talking about phase shift: kzbin.info/www/bejne/aWWqZaOwjNdsoaM

[@RideGasGas]

@@IMSAIGuy Thanks!

[@alexstone691]

From my understanding this can't be used for DC signal, how do you do an amplifer for dc signal?

[@IMSAIGuy]

Part I showed a DC circuit.

[@IMSAIGuy]

I have a series on transistor based amp that will show lots of DC circuit ideas: kzbin.info/www/bejne/kGmtdaasm7-dgpo

[@alexstone691]

Thanks, i always found this complicated so i find it quite interesting