Resistors, Part 2: Power and Wattage Requirements, Practical Applications of Ohm's Law 

It seems for those viewers who have a background in electronics or not and do have a love of guitar tube amps, will not find a better place to learn than from you! I have searched the web and I can't find any other channel that provides a more easy practical way of explaining and showing the incredible world of tube amps. There are others who do share good info on tube amps, but not like you. Not only the teaching but Rusty and Jack provide the all important human-pet aspect. We love you! Thankz

Uncle Doug I think your whole channel should be archived in the national library. You are a beautiful human-being. Thank you for sharing your knowledge. (and YES Rusty is included!!)

I would like to point something out that I don't see commented on very often; the amount of work required to produce a clear, concise and informative video. It's not easy! After watching Uncle Doug's videos I thought I would make a video and post my first amp build and I have been greatly surprised at how much effort is required to do it correctly. Lighting, camera angles and maintaining continuity has been a hell of it's own. I find myself getting caught up in the build and remembering several steps later that I forgot to turn on the camera, so I check the lighting, camera settings, etc. and try again. Other times I notice repetition in my explanation of a specific step, in which case I stop and do it over and over,and then try to pick up the build again where I left off. I have even documented some incorrect steps that I have had to delete or replace with something else. Keeping continuity is not as easy as it looks, and I think this may be the reason I see so many demos on YT of the finished product and not very many good videos of the build. Uncle Doug makes this look easy and it's not. Another great video.I feel like I'm in a classroom.

Uncle Doug is an excellent instructor.

Very clear explanation of Ohms law related to amplifiers. I think everybody has to know this basic calculations when building or troubleshooting an amp. Thanks!

Hi Uncle Doug & Rusty, I reviewed the Resistors Part 2: Power and Wattage Requirements, Ohm's Law. Looks like I have a little math to do, no problem, I love math. I have no problem taking your word for anything amp related, your a living legend on RU-vid to any one that is into amps. You can't beat the voice of years of experience. Thankyou so much for all that you share for those who need to know the correct and proper way of things. I hope your all having a great summer. Take care, C.

Jack seems both fascinated and totally annoyed by the flying drone. xD Thanks again Uncle Doug for helping me put practical use and relearning of my high school electronics. Now in middle life, I am revisiting my youthful aspirations to understand and practically apply electronics knowledge into my passion for music.

This guy is the real deal. I wish he lived closer to me as i love learning and i love vintage vehicles !! I forgot about the kitties and the dog. As i believe they understand more than we realize they know they have it made. Keep up the great work!

Great fundamental material and presentation. Lots of clarity..... I always like your sharing of some of your personal life.

awesome series! Like most of your tutorial videos, I get more out of them the 2nd time I watch.. my M.O. has been to watch it 1x, learn just enough to be extremely dangerous, tackle the subject, get zapped, burn up at least a few components & finish by letting all the smoke out of the wires. Then, upon re-watching the videos, it doesn't seem like chinese arithmetic & a lot of things become relateable & understandable. I built myself a cooking 5f6a 1x12 combo & I've had to figure out how to assemble it, wire it & troubleshoot some 60hz hum & tweak it into shape. it is an awesome amplifier, probably the best I've ever played thru. it largely was made possible off the education I've learned here.. As always, Thanks UD!..

Thanks from Spain! When I studied electronics, tubes was obsolete! Now, I'm repairing and building tube guitar amps, and love to learn from awesome teacher like you. Thanks again!

You are absolutely awesome. Your impact as a human being is being felt by many. Thank you!

Rusty & Jack displayed Ohms of resistance by turning down Georgette and the drone, respectively. As always, an extremely interesting and scintillating presentation. Thanks, Doug.

THANK YOU again for taking the time to make this series. This is making up for all the classes I slept through back in my teenage years. I actually get it now. Jack seems to enjoy the drone.

I cannot tell you how much you have helped me understand tube amplifiers and increased my general electrical understanding! I have been reading books, websites, etc for weeks on amplifiers only to have been able to name parts and maybe what they do but not understand it. After an hour or 2 of your videos I actually get it! You rock!

I love it! As we get older, food is the only thing that really matters! My wife would vouch for that!

I've been repairing amplifiers and effects (attempting and occasionally succeeding) for myself and friends for a while now, mostly through trial and error/things I've picked up along the way. Finding your channel has really opened me up to how circuits work. I've been taking notes and applying things I've learned from you, and I gotta say, I'm very thankful for the videos you make!

Great video Uncle Doug! Nothing like using the actual readings from a working amp to get "real world" understanding of what's going on. A lot of useful info provided. A nice follow up to your previous video. Can't help but love the practicality of those old Valco amps.

Great video, as usual! Thanks Uncle Doug! Glad to see the two laggards are finally "off the dime" and back to work! I have that same type of volume control knob on my 1958 Gretsch Electromatic guitar! Love that "G!"

Great two part video! Very helpful and enlightening. Thank you!

Thanks again, Uncle Doug! Great job, as always!

Another great video Doug. I learned a lot. Thanks for taking the time to make this and post it.

Very productive and informative! Thanks for sharing your knowledge sir!

straight to the point!!! excellent videos uncle Doug, thanks a lot

Poor Rusty...”Other dogs in the neighborhood don’t have to deal with these weird tests! Arfff!!” I’m learning too much. These really are great videos! I can actually follow what the Guitologist is doing in HIS videos much better now,too.

I love this channel !! Thank You!!

Legend! So good, so useful and to the point! Many thanks and keep 'em coming!

I'm loving these videos, your teaching style is superb! You're telling us what's going on without talking over our heads. On to #3

Quite helpful. I've been shown how to connect for bias measurements, but I like seeing it on the schematic better. Much better in my brain than before.

Excellent vid, Uncle Doug, as usual...

Love this series!

I must be a supernerd. I love your shows. Very informative and a certain 3 stooges meets monty python vibe. I'm glad Rusty is still helping out.

Thanks for sharing your knowledge!!

great video Mr Doug

Just totally awsome, thank you so much.

I'm glad to see that Rusty is doing fine.

You are a great teacher! Thank you for these videos. Im batting around taking some electrical engineering classes. It has always fascinated me. And I love math lol! Just got my first tube amp and I want to know how it works.

Hi Doug! I just started watching this series and I'm glad I did. I've browsed your videos for quite a while but always skipped this resistor series thinking it was going to be too basic. But I'm now adding it to my playlist of tube amp working principle :) Btw, seeing your gorgeous 6150, it must be the exact same amp as my little Supro Super 1606b. Even the speaker looks identical.

Thank you uncle Doug, Rusty and Jack for the excellent series of videos on tube amps and other related things. So far, I have not come across any such informative and we'll explained videos such as yours. I just wanted to add something to your explanation on power. Firstly, we measure energy in Joules and power in Watts. Watt is an alternative name to the original unit of measure, which is Joules per second (J/S), named after the scientist, James Watt. As you can see, power is simply the energy consumption rate or how many Joules consumed per second. As an example, a 100W electric bulb consumes 100Joules of energy (electrical) during each second of its operation. Unfortunately, we cannot possibly covert all that electrical energy to light energy. For example, maybe 90% of that energy would be converted to light energy while 10% maybe lost as heat energy. Considering the topic of resistors, for example a 1W resistor is capable of safety dissipating heat energy up to 1 Joule during each second of its operation. Assuming that all the electrical energy in this resistor is converted to heat energy, we could calculate the maximum current through this resistor using the formula I=√(Power/Resistance). If the resistance is 1 Ohm, then the maximum current would be 1A. If resistance is 100 Ohm then the maximum current handling capability would be √(1/100) = 0.1A, without burning the resistor. Cheers and looking forward to seeing more interesting videos from Uncle Doug and his team.

why you are so outstanding.... Grace teaching style......

very interesting uncle doug thank you

VERY GOOD...THANKS!

Thankyou for your time and it was not wasted as l am learning a lot thankyou 😀

Hi Doug, thanks for the great video! I'm now going to work just before the weekend, starting with a big smile on my face:) This amp is an great condition. Is it really 50 years old? Unbelievable!

Thanks Uncle Doug. I'm sure that was an elementary question but helped me with my notes trying to learn at my age.

Excellent tutorial Uncle Doug. That amp is very clean looking. I'm restoring an old cc 1980's slave power amp (solid state not valve) and internally it was a right old mess. Full of dust, fluff and rusty terminals. I'll release a video of still photo's when it's complete - I'm completely refurbishing it with new components. I also discovered that you can use the wife's nail varnish remover to clean the PCB tracks of flux residue, although don't try this on the screen printed side as the component markings are removed..

great video. thanks. looks like Rusty's found happiness in life..and Jack was almost a victim of an in house fly by..cool amp btw too.

again, very well explained Uncle Doug. i'm getting addicted to this serie 😉. oh.. can i say, Rusty made the best choice.

Would have loved to have you as my teacher! Just starting to learn about tube amps and I enjoy the way you show how things work. Bonus , I have a black cat which is a clone of yours! Looking forward to all your videos. Leo, Montreal, CANADA

very helpful video doug.. thanks! Im not sure Jack was impressed by the drone!

Gorgeous Amp.

The Teach is back. thumbs up.

using resistors that are twice as large as what they're likely to encounter is a very good idea and i'm doing that in the project i will start soon

Great videos! I like them alot. I had a thought about drawing the B+ from pin 8 of the rectifier. It matters if you ever intend to use a solid-state plug-in rectifier instead of valve rectifiers. I hade my amp wired to take the B+ from pin 2, which was all fine. Then I plugged in an octal socket solid-state rectifier I had bought. The new rectifiers cathodes were only wired to pin 2 causing my amp to draw all the amps current through the 5V filament winding. Which might be bad, I don't know. But drawing B+ from pin 8 seems to be standard in most circuits you see.

I stay every day looking if you put something new video in your channel. That's like a food for my brain and my soul. "I'm addicted on Uncle Doug Channel" Master, do you have some other site to view these schematics beyond the "Old Frets"? Thank for share a piece of your life and time with us!

Uncle Doug, once again you have concisely yet thoroughly explained a difficult subject. (It is not surprising to discover you were an algebra teacher; much respect sir!) Here's a question about resistor wattage in the context of longevity: do higher wattage resistors tend to drift less over time, and does it depend on the material? For example: an amplifier from 1971 has a 15k 1/4 watt resistor in the tone stack, 100k 1 watt plate resistor, (both carbon based,) and 1k 5 watt ceramic resistor in the power supply. If one were to test the values of all three, assuming they were within 5 - 10% tolerance when the amp was built, which, if any, would remain closest to its original value 45 years later? (Assuming, of course, that the amplifier was all original and in good condition.) Thank you once again for sharing your knowledge!

Another amazing and incredibly informative video! A request: not sure if you've done this in the past catalogued in another video, but could you make a video on your method of properly discharging capacitors when working on an amp? There seem to be many methods out there, but I have a feeling I'd like to follow your way. Many thanks! -Alex

Hi Uncle Doug. After scouring the internet for better understanding of how tube amps work, your videos have really helped me clear the fog. I have a "learning handicap" in the sense that I find it difficult to assume things and move on without actually understanding how things exactly work, the purpose of each component etc. Your videos have been a cut above the rest, in that, you do not assume that the viewer has prior working knowledge or that something is too obvious to explain. You actually explain the function of every component. I really appreciate this. Thanks for your efforts. In the schematic you show, I have two questions 1. In the first input stage there is no cathode resistor. Can the circuit still work satisfactorily? As I understood from your other videos, the cathode resistor serves to put it at a more positive voltage compared to the grid for biasing purposes. Here both grid and cathode are effectively grounded. 2. What is the purpose of the capacitor on the primary winding of the transformer connected to mains supply. It looks like a filter cap but why would I need to smooth out the input AC voltage? Thanks again for your time.

Thanks UD.....Carl

Uncle Doug, amazing video as always! :) When you're measuring the resistance in-circuit, aren't you actually measuring the resistance in parallel with the whole circuit?

Power : Defined as when one’s wife threatens to divorce you because your spending too much time working on amplifier circuits. Boy iam going to miss her!!! Hahaha 😂 Glad im not married!! Thanks Uncle Doug your videos are so intriguing that Iam now fully engrossed in learning all about tube electronics despite having an Associate Degree in Electronics Technology that i earned back in 1995. We learned so much solid state theory then but sadly, didnt learn repair techniques much then back in the early ninetees. We were more focused on design and the ciriculum was designed to transfer to a 4 year program or gain entry level employment in the field. . I distinctly remember that we built a 50 watt push pull transistor amp that was powered by a low powered sony walkman hihi.. and that was the extent of amplifier design projects we were involved in then. Sometimes we just memorized information and regurgitated it until it became habit and kept on chugging along just to cover all the information in the semester. Your style and instruction is superb and i understand everything you show us. Tubes are so much more interesting and rewarding in my opinion to learn and will always retain a niche use in amplifiers and communications applications in the electronics field. Thanks so much for all of this instruction iam really enjoying this series and learning alot :)

My Hewlett Packard HP48 will let me plug in numbers and it has Ohms Law & Power built into an equation library. It has the RC RL RCL circuits and phase angle changes in voltage and current, reactance, reluctance, impedance, resonant frequency, inductance, etc. etc.

Hi Uncle Doug, another great video, thanks. I have a question related to resistors, I am planning to scratch build a Fender AB764 amp from parts found at garage sales but am a little confused regarding potentiometer selection. The schematic I have only specifies values needed but not type (A or B). Does it matter or is it important to use the right type for volume, tone etc. Any guidance would be very much appreciated.

I love the clarity of your presentations. I notice that you almost never stumble over your words, using um or uh to fill the gaps. I wonder if you read from a script (doesn't sound like it) or if you were a teacher in your career?

Another brilliant video, thanks. Do you have one that works backwards - how to calculate expected voltages and currents/power in a valve circuit without having the actual circuit built i.e. I want to build an amp but do not know voltages apart from the HT or wattages for each resistor???

Really Interesting video! A few questions came to mind as I watched it: 1) Why doesn't the cathode on the first 12ax7 have a resistor? 2) What is the purpose of the .001 coupling capacitor that bypasses the volume pot on the way to the grid of v2? Does this mean that the volume can never by completely shut off since some of the amplified AC signal from v1 always gets to the grid of v2? 3) Why does v2 have a larger resister (270k) on its anode DC power than v1 (100k)? P.S. Rusty and Jack need a patreon page so folks like us that appreciate their hard work can upgrade their treats and toys! Thanks for the great instruction. -Gerald

Great stuff, Rusty (and Uncle Doug). Good content, and excellent presentation. You'd think you taught for a living or something... :-)

AWESOME as always! Have you been bitten hard by the drone bug? The Nano QX is a gateway quad and I can only imagine what you might be flying nowadays.

Greetings Doug & Rosty!!!!

6:56 Stock as a what? I haven't heard that expression before. Googled around, but I must admit my ignorance. You've set yourself up for an excellent mini-series here, Uncle Doug. You could highlight just about any aspect of amplifier circuits, layout do's and don'ts, capacitance, inductance, etc. You're booked right up until we put you in a home--or they put ME in one... Another delightful video, suitable for repeated clobberings over my head for retention. My highest compliments again. And that Gretsch is certainly NSFW. Nice. Ironic, really. I have had nothing but fear and dread toward all Algebra teachers to date.

Very good demonstration Uncle Doug. I found it interesting on the Resister wattage. Now I have some 2 watt 270k & 470k ohm resisters I have been using in filter Cap usage. All seems to be ok so far. Now this is over kill I'm sure but could it lead to an issue? In my schematic some of the 270k ohm resisters have 10% wrote by the resistance value.

Like the way you explain all this doug, your videos have been an invaluable resource for understanding these concepts in an easier way. Question? : How is it that you are showing on the schematic that the power going into the tube is coming from the (Cathode pin 8) ground leg? I guess you are just measuring the voltage across the 1 watt (330?) resistor ? Please clarify, Im not seeing this right. Thanks --

Hello uncle Doug. I am new to ohms law and finding it facanating. Q. in the cathode bias resistor,356 ohms. why would you ground/earth it as shown in the schematic? I conceed that I have missed some thing fundamental here. Great video.

Digging your videos Uncle Doug! Any recommended websites to order variety packs of resistors and capacitors?

Well done as always. Rusty's choice went the way I thought, but love seemed to slow him down a bit. :)) Jack looked to be thinking up all the four letter words a cat might know. :)) Andrew

Hi Doug :) Thank you for this Video and all the other informative and well done work...Have to say.. Anode Current and Cathode Current Minus Screen Current, Very interesting and begs the question....with regard to Tube Matching....Would it be possible to Build a Tube matching device other that a tube tester for matching output tubes..? Also,,Can you do a Video on Tube testing...Triodes preamp tubes and power tubes..Thanks Doug.. Terence.

Another newbie question for you Doug. At 8:43, is it possible to determine plate current just from looking at the schematic? I am looking at a schematic and I have the plate and cathode resistor values and the B+ voltage at the transformer, but not the voltage drop across the plate resistor. It's a 12AU7 tube. Any tip on how to figure that out?

In my school (portugal) they taught volts as U instead of E (E is for energy in joule, J), so it took me a little while to understand some equations. Is it one of those US and EU preferences/disagreements in notation? Also, when you taught/teach physics how do you teach your students the notation? Thanks for the videos!

Your pets have made two interesting observations - perceived female fickleness (poodle) and applied aerodynamics (quad 'copter). Great lesson Doug. You mentioned 'Ballast Resistor' at the beginning but not as an application - later perhaps ?

Something tells me Jack has encountered that aggressive mini-drone before !! ;) ;)

Thank you Doug.In this video you use the term "voltage drop". Is this always the voltage measured across a resistor and that term is "voltage drop"? So the voltage drop is the number you use in the many calculations where "V" is a factor? The term "voltage drop" is not to be confused with any other voltages like the 6.3 filament or 5vac.These are set voltages. I think I get it now. Thank you

Great video! But I always get confused on which components must be unattached when taking measurements of components in a chassis. I know voltage measurements are taken with components undisturbed when but measuring resistance and capacitance confounds me. It looked like in your video that when you measured resistors that they remained attached. Do I have this right?

How do you calculate the volts and current coming through the cathode if your trying to build an amp and don't have anything to hook the meter up to?

Hey Doug. I noticed on this example you measure plate voltage from plate pin 3 to pin 8 cathode instead of from plate to ground when using the cathode resistor method.. They are the same i guess. If there is a difference please let me know and if it does not matter I'll just use either way. Thanks

Uncle Doug, you're videos are the best! Pass some love onto the furry ones too, plz. At 20:37 you show the circuit requiring .564W to pass thru that resistor (dam)... And you then say double it for safety. Did you not say earlier in this series how that would be like throwing a hotdog down a hallway? How the high wattage resistor would have little affect on the lower flow through the "dam"? I've learned so much from these videos, so thank you so much. But I'm baffled on this one, perhaps you could clarify in the future? 🙏☯️

Hello Doug, in a double ended PP EL84 Class AB amp with a 300V B+ into pin 9, 295V out of the plates@ pin 7 and bias resistor of 130 Ohm from pin 3 (which also includes a 25 uF cap), the power rating of the resistor I have seen is 10W. This seems high. Is there a reason for this. Perhaps because there are two power tubes?

I wish i didn't have to ask questions Doug but i'm not the sharpest knife in the drawer. I guess if its grid bias you can't use the cathode resistor method since the cathode is grounded and you could go from pin 3 to pin 8 of the 6V6 or you have to use the OT measurements to determine voltage and bias with a fixed bias amp. I was just curious about cathode bias and getting plate voltage from pin 3 to pin 8 and if pin 8 and ground were at both the same potential in a cathode bias amp If you think my questions are silly or tedious i'll get the hint if you just don't want to respond. I was good with measuring voltage at the plate by measuring pin 3 to ground and then i saw you use pin 8 instead of ground and was wondering if that was just for fixed bias or cathode bias as well? I keep watching your videos since they are fantastic and it troubles me i can't figure it out without having to worry you about it since you probably already gave the answer. Thanks

1:52..."E" for "Electromotive force" and "I" for "Intensity".

Super Nice applications for Amp Analysis.....using the lesson. Works better in my head. ps: the Director, Actor, LIghting, Writing guys that work for your Videos are really good.....(they may want to know about paypal's tip jar)----they are that good! KaChing!

+Uncle Doug Thanks for these videos! They are very informative. I have an electrical question that has always bugged me. How does electricity flow to/from the ground taps? I notice that you measured voltage across a resistor that goes to the ground. Seeing as there's no actual ground wire from the chassis, I'm assuming that the electricity actually flows through the chassis of the amp to the neutral return. If so, wouldn't this be able to create a current through the chassis that could shock someone? Also, what is the benefit of having a ground tap, if the current returns to the power transformer, and ultimately back to the neutral? Does it somehow get rid of excess voltage? I'm missing something somewhere. This whole concept has been one of the biggest stumbling blocks for me when it comes to learning about electrical circuits in general.

question for unc. doug; hi unc, I am receiving a Tandberg model 3341x reel to reel deck. It is wired for euro voltage. It has a euro plug on it. I want to use this deck if I can get it operating properly. Would you suggest changing the power transformer or trying one of the step up voltage transformers for sale on line? thanks UD

May I asked a Question? I have a 50 watt 6v6 powered amp. it's push pull, I've removed the two outter tubes , one died on me. So I though it would be nice to cut down the power on this one is that Dangerous? In my understanding it is not. Also what other power tube could be exchanged for the 6v6's? Thanks

You should make a Best of Rusty video.

I wonder why there are so many variable names for voltage. Here we used U for voltage, V seems pretty universal and common, and then there's E. There must be some history and origin to those. U might just be to be clearly distinguishable from symbols like small Nu. I suppose E has to do with potential energy? I tried calculating the plate dissipation from P = I^2 * R, but got wildly different results than with P = V * I. This makes sense when double checking the "plate voltage" via V = R * I, where the voltage calculated is actually the ~10 V voltage drop over the output transformer (or the voltage drop over cathode bias resistor), but what would you use to calculate this instead of measuring the plate voltage itself? You could calculate this of course from rectifier potential - output transformer voltage drop, but that's still measuring it, actually measuring it at two points instead of one. I take it you can't calculate that plate voltage unless you know the starting voltage of the circuit and know every resistance in the path, calculating all the voltage drops and summing them up, until plate? For the record I couldn't get anything sensible from cathode either, but I was under the impression that you could use the P = I^2 * R as well, so is there a current or resistance I should be using instead of the ones measured? Maybe I was mistaken and it was P = V^2 / R, but that doesn't yield correct answer either (the resistance probably being the problem here?). So essentially I only managed to calculate the cathode bias resistor's heat dissipation power, as well as the same thing for output transformer. This is a funny place where I went through physics in high school easily and didn't have trouble in the basic electronics physics in tech uni either, but I'm lost with as simple thing as this :) Time takes its toll I suppose and I never really learned the actual workings and rules and applications in circuits. So when you're designing your amplifier and can't measure say the voltage drop in the cathode bias resistor, do you look at the heater supply and use that voltage to calculate the voltage drop over the cathode bias resistor and get the power rating like that, so you don't have to throw in a resistor and power up the amp and start measuring what the actual power rating should be? It's sometimes a bit confusing when the schematics don't connect everything, I tend to forget the heater supply when the schematic doesn't show that it goes to the tube, only the grounding from the other side of the heater. Say there's the power supply section in the schematic with A+, B+ etc (high voltage supply for plate side of the tube?), then the tubes are labeled V1A/B, V2A/B, V3A/B and there's the other side of the power supply "opposite" from the high voltage windings, that's V1F, V2F, V3F and goes to ground. I assume these would mean the heater connections, but I'm also left to wonder where C, D and E went. The nodes at VxF are labeled 4, 9 and 5 so I assume those would be the tube pins? Maybe this is explained in the tube and power supply transformer videos.

Thanks a 6150 eh? That sounds like the Grand dad of the 5150, lol jk. I really enjoy your teaching & thank you for sharing this knowledge. This is like a great way to relax listening to a real american man that is NOT the numb skulls they make men out to be on TV. You are a Gem Uncle Doug. Gods Bless you & yours.

How practical is it to rewire a dual 6973 output over to EL84 ? I'll wait on your very very professional answer with baited breath. Thank you very much. Love your videos. Say hi to the crew for me thanks.

At around 11:55 you say that you are going to subtract the resistance value of the test probes themselves. How do you know their actual resistance values? Is that a spec that you can find from a manufacturer specification? Just curious. Also, is the tube "screen" the same as the "grid"? Sorry for the (probably) silly question, just learning this stuff now. :-)

Hi Uncle Doug; This question is not related to the video. I noticed a .001uf (one nano-farad) bright cap shorted across the terminals of the volume pot. Is this to provide mid-range punch at a reasonable practice volume, as bright caps usually have a much lower capacity? Thanks for the education.

I thought ground was positively charged and electrons flow from the power source to ground. Also that current flows opposite of electron flow, which means from ground to the power supply. In the case of direct current like in this amp, what happens in the ac dc converter to allow proper flow and type of current?

Uncle Doug, being very green to electronics a question is there right and wrong way to install a resistor? + or - wise?