# I have a problem with formulas & schematics (warning, long post)

#### martinlb

##### TDPRI Member
I work as a teacher, and I hope none of my students has ever thought a mean-spirited one. The difference in learning from concrete examples versus learning from abstractions and generalities (a rule, a formula) is a difference a lot of learners have. A lot of instructional material fails to support that style of learning.

As soon as you want to know how much current is running through a resistor (for example to bias a tube), or how much voltage is dropping across a resistor (for example to know why the first dropping resistor in a Champ is 10k Ohms and the second dropping resistor is a 22k), then you can use Ohm's law. It can be question/curiosity-driven, and it can be attached to one particular moment of curiosity, and never mind if you end up asking the same kind of question a bunch of times. Memorizing the general formulas or reading through an entire chapter of a tube amp textbook and forming an abstract understanding of the topic can be a really heavy lift for anybody.

Since you're self-motivated, there's no time limit, there's no need to learn efficiently, there's no quiz or people to impress. A question as simple as 'What would changing this coupling cap here do?' opens the door to some really useful stuff, and a person can pick how far to take it.
Thanks. It sounds like you're the kind of teacher I would have loved as a kid. What you say about abstractions vs. concrete examples is 100% accurate. I appreciate your suggestions.

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#### martinlb

##### TDPRI Member
Did James Clerk Maxwell complain about teachers and textbooks? Did he have multimeters and oscilloscopes? Or YouTube? Or Fender amps? Or community colleges? No. He had a cat, an amber rod, and maybe a DIY electroscope. He didn't even have formulas initially, until he wrote them to torture the rest of us.
I guess I'm not really sure what point you were making. Would you mind elaborating? I don't want to simply assume I understand.

#### martinlb

##### TDPRI Member
Have you tried getting a decent text or working through an open course?

In a decent course you'll start small and work up to more complex circuits, and work through lots of example problems to get familiar with how to apply the concepts.

Also you can do experiments yourself if you have a battery or power supply, some leaded components, and wire, perhaps a breadboard, and a digital meter. Later you can get a low cost USB oscilloscope, and probably a signal generator, as well.

For example:

Yes, I've signed up for, and even paid for, some online courses. One of them, in particular, is taught by someone who clearly understands the theory behind tube amps and electronics in general. The problem for me was that his homework assignments pushed me into the very areas I need to succeed with, but I think he may understand those things so well and so clearly that what he may have trouble with is understanding those of us who don't understand.

I will check out the MIT courses, thanks!

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#### martinlb

##### TDPRI Member
If you are going to work with Valves/Tubes while understanding what you do you must learn "loadline principle"!

Begin A-class and you understand how triode pre amp resistive stages are set. There Ohm Law is used to set Operating Point (bias point) to loadline selecting Operative Voltage, Anode Current. OP and cathode resistor.

Then advalce to power pentode which use a Single Ended Output Transformer.

When you increase SE bias current setting negative Control Grid-1 voltage which lift OP up and OT becomes "pre loaded with energy". Same time the end of loadline on right moves to the right and potential for Anode voltage sweep doubles what actual Anode voltage is. To me this is most interesting feature on OT!

Also how the Anode Current potential on left end rise when Loadline rise and there comes possibility to produce power to the OT Primary Impedance making OP move. Then study g1 curves which are needed to make OP move and this is called Drive Signal. Sometimes a Water Valve is used to explain how vacuum tube operates.

Then study OT "winding ratio" and you understand how high voltage/low current tube power sweep is turned to high current/low voltage loudspesker signal.

Then advance to Push Pull AB-operation and then distortion/clipping and you have very good understanding how tube amps operate.

When studying use this loadline calculator. After you select a tube it often pre loads default values and you can change only one parameter and immediately see the effect it has to loadline. At first use 12AX7 which is most common instrument amp tube.

Then select 6V6GT which is used in many guitar power amps. Its SE OP gets too much to the right so first change V1=anode voltage and Bias Current so that OP comes center of Loadline.

If you don't hate e-books you could buy Giuseppe Amato book of loadline designing. It was only \$5 when I bought two years ago. Everything is possible to learn in internet pages but it has everything needed. Perhaps it is in paper too but I think will cost more?

Thanks 2L man. I'll keep the progression you're recommending in mind. I may, though, have trouble at this point with some of the complexities but I'd hope that as I learn I'll get there.

#### Sconnie

##### Friend of Leo's
Did James Clerk Maxwell complain about teachers and textbooks? Did he have multimeters and oscilloscopes? Or YouTube? Or Fender amps? Or community colleges? No. He had a cat, an amber rod, and maybe a DIY electroscope. He didn't even have formulas initially, until he wrote them to torture the rest of us.
He was one of the most gifted physicists in history! He did it all on paper too, he was not an experimentalist. I could go on about that guy, he's one of my favorites.

Anyway, addressing the OP now. Going from a schematic to an actual layout is one of the first challenges of stepping into electronics. Schematics are done in a standard way to make them easy for engineers across the globe to understand, and they never match an actual layout. Take them in bite sized pieces, no one learns a schematic by staring at the whole thing all at once. Figure out which chunks correspond to each part of a circuit and learn them one at a time. Eventually you will learn to spot power sections, data/signal manipulation, safety interlocks, I/O modules, and now I'm digressing into industrial control panels... it's all the same though.

Formulas are tough to get around though. At a certain point you will just have to step up to the plate and power through, but in the same way I described above. Stick with the simple manifestations of Ohm's law, Coulomb's law, the basics. You really only need algebra to do guitar/audio electronics, no field theory required (Maxwell's equations).

To build intuition without a penny of investment in equipment or supplies, use these tutorials from CU Boulder. Their physics department is really great, and I'm not just saying that as an alum. We used these tutorials throughout my entire undergrad, not just gen phys 1.

#### Sconnie

##### Friend of Leo's
Another thing! The math that governs electronics is eerily similar to the math of fluids. The best analogies to circuit flow is water flowing in a pipe. Voltage is analogous to pressure, current to flow, resistance to drag, transistors to valves, the list goes on. I'm sure the internet is full of elaborations on that analogy. I hope you can build some intuition with that too, good luck!

#### guitar_paul1

##### Tele-Afflicted
@martinlb
"What I'm working on now is rather than the two channels playing clean the sound is like that of overdriven tubes - it's distorted even at the lowest volume levels. It also breaks up with static-ish sounding noise when I hit the strings hard."

Sounds like maybe a leaky cap feeding the grid ?
That can allow DC from the previous stage to bleed thru and goof up the grid voltage?
Check screen, plate and grid voltage and see if they make sense. At least that's where I would start.
Hard to say more without a schematic.

#### Kev-wilson

##### Tele-Meister
I found the Uncle Doug videos on YouTube to be very helpful for an Ohms law refresh, I can rearrange equations but was hazy on amps (i amps just as much as bottle amps ) & watts so seeing the guy using it in its different forms was great. I also found (still find) the RobRobinette site to be very useful as a learning and reference tool.

#### martinlb

##### TDPRI Member
He was one of the most gifted physicists in history! He did it all on paper too, he was not an experimentalist. I could go on about that guy, he's one of my favorites.

Anyway, addressing the OP now. Going from a schematic to an actual layout is one of the first challenges of stepping into electronics. Schematics are done in a standard way to make them easy for engineers across the globe to understand, and they never match an actual layout. Take them in bite sized pieces, no one learns a schematic by staring at the whole thing all at once. Figure out which chunks correspond to each part of a circuit and learn them one at a time. Eventually you will learn to spot power sections, data/signal manipulation, safety interlocks, I/O modules, and now I'm digressing into industrial control panels... it's all the same though.

Formulas are tough to get around though. At a certain point you will just have to step up to the plate and power through, but in the same way I described above. Stick with the simple manifestations of Ohm's law, Coulomb's law, the basics. You really only need algebra to do guitar/audio electronics, no field theory required (Maxwell's equations).

To build intuition without a penny of investment in equipment or supplies, use these tutorials from CU Boulder. Their physics department is really great, and I'm not just saying that as an alum. We used these tutorials throughout my entire undergrad, not just gen phys 1.

The bite sized approach to schematics sounds promising. And thanks for the link.

And the encouragement.

#### martinlb

##### TDPRI Member
@martinlb
"What I'm working on now is rather than the two channels playing clean the sound is like that of overdriven tubes - it's distorted even at the lowest volume levels. It also breaks up with static-ish sounding noise when I hit the strings hard."

Sounds like maybe a leaky cap feeding the grid ?
That can allow DC from the previous stage to bleed thru and goof up the grid voltage?
Check screen, plate and grid voltage and see if they make sense. At least that's where I would start.
Thanks, I'll check those.

Hard to say more without a schematic.
Without a WHAT???

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