Biasing Basics, Class A

[sloppyoscar]

Interesting stuff. I was wondering if you can measure the grid voltage with a voltmeter -- black probe connected to chassis and red clamped to grid pin on tube. Is that safe? I'm new to alot of this and don't want to get toasted

[AllAmericanFiveRadio]

@sloppyoscar

I always use an isolation transformer. And with power on, I only work with one hand. The best place for your other hand you are not using is in you pocket. So I set everything up first before applying power. Download my ebook, you can find the link on my channel, page 105 would be a good place to start.

[sloppyoscar]

@AllAmericanFiveRadio Thanks! Will do so.

[lai2ke4]

HI, first thanks for the excellent expanations . I recently got a hybrid tube amp and tried to roll some tubes on it. I used an oscilloscope to mornitor the output. It turns out only one out of five tubes I got can get the perfect signal shape without distortion, and I checked the bias voltage for that "good" tube and found it is way below the specified value for the circuit. Does that mean most of my tubes are actually no good or the circuit design is problematic?

LK

[AllAmericanFiveRadio]

@lai2ke4

Check into why the bias voltage is low. That could be the problem.

[hermeticoguitar]

WOW.

This is a real Master lesson.

I highly appreciate this info. Clear, graphical and absolutelly cleaver.

THANKS A LOT!!!

[AllAmericanFiveRadio]

Thanks hermeticoguitar

[neutroniumamp]

I'll be getting back to this AAFR - it does take some time and patience to grasp and for now sans a DVD my only complaint is the quality of the schematic drawing. Nice sharp crisp lines would make learning easier but your slow and methodic voice helps. If more musicians educated themselves on this stuff, they could argue a pitiful amp head repair cost based on knowledge as power.

[monahf]

hi and thank you for this useful video :)

i have a little question, actually how u know that this resistor and that capicitor is for biasing how could u realize that?? is it with experience or a method to follow?? and how could u make the difference between class A, B ..... etc.

is it some method to follow I m really lost.

thx

monah

[AllAmericanFiveRadio]

Thanks. That information is supplied by the manufacturer. The manufacturer who wants to sell their produce, supplies the customers (engineers) with sample circuits and data useful for the customer. The manufacturer gets this circuit and data information by the work their development engineers do in their laboratories. So the bottom line is the information is supplies by the manufacture.

[AllAmericanFiveRadio]

And you can look at existing circuits to get this information. A particular produce has to be used the way the manufacturer intended or is simply will not work.

[monahf]

ok thank you :)

So lets suppose that i found a new circuit, though without the shematic circuit , it would be impossible to understand the way it works?? and would it be impossible to understand this R or such C aim to which objective?

thank you

monah

[AllAmericanFiveRadio]

Hey Monah,

Sure! I do it all the time with old radios. When I can not find the wiring diagram I make my own drawing of the circuit. This makes you concentrate on each component as you draw up the circuit. It is a very good way to understand circuit design.

[monahf]

thx u so much its much clearer now.

[Albinorama]

1000x Thanks.

I finally know what Biasing is!.

Always thank you very much.

Put all these videos together and I will buy the DVD ;)

[AllAmericanFiveRadio]

Thanks. It makes me happy that the video helped. I may do a DVD, might be a good idea.

[zbyszekskibinski]

very good and valuable video, you're a great engineer and and good teacher too, many thanks for that.

[AllAmericanFiveRadio]

THANKS!

[cometogetherband]

I could never fully understand biasing but I do now! Thank you Rick.

Mike

[AllAmericanFiveRadio]

You are welcome and THANKS!

[windoes98se]

yup, thats hou the distortion works on my guitar amplifier

[AllAmericanFiveRadio]

THANKS!

[eufaula1]

Excellent video Rick! That video filled in a lot of the gaps in my knowledge about old radios. Thanks again.

[AllAmericanFiveRadio]

Hope it helped! Thanks.

[BadEditPro]

Interesting video... I've set bias before but by doing exactly what the service manual said to do.... It's nice to get a clear picture of what's really going on. You might consider doing a similar video on push-pull circuits. I'd love to have that broken down the way you've done this. :) JC

[AllAmericanFiveRadio]

Thanks. Ill put it on the too do list.

[Lockemeister]

Thanks for this video. I was wondering what those resistors did in the schematic. I just replace the ones that seem too far out of tolerance, but don't really know what they all do. This video really helps!

[AllAmericanFiveRadio]

Thanks. Lost of drawings in this one and this is the third upload. I am happy with this one. Thanks again.

[AllAmericanFiveRadio]

The engineers who design these circuits use their schooling, passed experience, lab work, and information from the manufacturers about the tube/transistor and manufacturer example circuits. The manufacture engineers use their labs for developing circuit designs so they can sell more tubes and transistors est.

[Lockemeister]

I don;t feel as inadequate now for not understanding why they capacitor bypass a biasing resistor that goes to ground in the radio I have. Or maybe it's not a biasing resistor. At any rate I hope to power it up ina few weeks.

[AllAmericanFiveRadio]

OK! I think I got it this time.