"Paint By Numbers" Amp Building

[Phil_S]

I've learned much of what I know from people willing to share and be patient at on line forums. I've also been willing to do some reading and try to think for myself.

I've noticed a few different "types" hanging around at on line forums. The "problem" type (and I've been in that role sometimes) is the one who is not engaged with his problem, isn't making the effort to think it through, is failing to use good scientific method to examine and separate a problem into parts. For people like that I think it is still important to help where you can, for doing nothing may leave them in grave danger. Sometimes, I think we hope that a bit of painting by numbers will help lead to real knowledge even though we know that is not the path.

Most people, though, seem to be genuinely receptive to the knowledge people share and to show enough honesty to say what they don't know or understand. I've "met" some people who know things that I think are in the stratosphere, who have been more than generous with their time by sharing with others.

For the few who may be problem builders, the question is probably what to do about giving them answers. I can't really make a great suggestion. I, for one, am not a kit builder. I built my first amp from a kit. That was my last kit. I've built a dozen or so in the last 7 years. I've got a couple that, while not really original designs, aren't cookie cutter from an F or M schematic/layout. Some of them had build problems and some didn't. Without the on-line forums, I may not have solve the problems. So, I put it to the collective, it is important to answer people's questions, no matter how badly crafted or how in over the head they might seem.

I do agree with the OP. It is ill advised to dive into a complicated amp the first time. Some get lucky. I read over at 18watt.com about guys who do one of those as a first amp and it works perfectly the first time (mostly the exception, not the rule). That two tube amp, it gives the new builder an opportunity to build manual skills (solder, lead dress, etc.) and get some practical experience and a fairly simple but satisfying project. I see regularly where suggestions made for first timers go in this direction and it feels right.

I'm not really sure what to do about people with bad judgment who show up at on line forums wanting an instant fix. My inclination to say, let's slow them down, try to school them were we are able, and maybe help them get the project to the finish line.

I can't help but remember when I didn't understand all sorts of terms like lead dress, voltage divider, coupling cap, filter cap, B+, dropping resistor, plate load resistor, slope resistor, sleeve, tip, etc. Patient people explained with written words, for which I am eternally grateful. I am quite sure I may have been a problem poster at one time, and maybe I still am. This is about having fun with amp electronics. Try to keep it that way. Choose where you like to participate, and skip the rest.

BTW, this is a great forum and I want to say how much I appreciate all those who may have walked me though a question that was important to me, and who gave me a wide berth when I've made an error in the guise of trying to state a fact that just wasn't.

[boldaslove6789]

I've spent a few years modding/building pedals and in the recent years I've got into tube gear. I'm only 21 and although I have read a lot of tube literature, I've learned more from this forum about amps (and different characteristics of certain parts etc.) then anything. I still have a lot to learn yet (It never stops ).I'm more of a guitar player than a tweaker but my rig sounds better than ever right nowbecause of this forum! Thanks to all you guys on this forum who have taken the time to help and have even went as far as sending me stuff!

[M Fowler]

Paint by number, Leo Fender included layouts along with his schematics, only makes sense.

I don't think many amps in the Forum world would get off the bench without the layouts.

I started in electronics as a kid with those electronics labs build buzzers and all kinds of crazy circuits. My dad brought home electronic junk for my brothers and I to play with. Had many of those Platform spinner you know it turns the 45 rpm records and you plug it into what ever device you had for sound. We were DJs when the word wasn't eve coined yet.

Fixed everything insight and wrecked even more. The old radio on the shelf in the basement, no cabinet would shock me everytime I tried to tune it in. From there the console amplifiers would become my guitar amps with the single or PP 6v6s and volume, treble and bass pots nice.

Went to school for Electrical Electronic Engineering but had to drop out and raise a family, a good thing. But that schooling never taught me anything about tube technology. Messing with my Fenders did. It was about 3 years ago ? I discovered this place after being curious about those great looking Trainwreck amps and the rest is history. Good folks and tons of knowledge with very smart people to look up to, thanks you freaking gear heads.

Mark

[dreric]

I am one of the paint by numbers kind of guys. In the past fifteen years of tinkering I've fixed about 50 amps, and now build 4, soon to be more. I've never shocked myself or blown anything up (well maybe one Ampeg) I have a lot of respect for those of you who have more knowledge than I and share freely.

IMO, most of my problems come from trying to avoid the math. I had the same challenge in chemistry and bio chem, yet I learned those. When most people say "theory" it really means understanding the concepts and making them real by applying the math. The math is always where we want to skimp.

For me, there have been several missing ingredients in becoming more proficient:

1. There is no testing. IMO, the only way you learn theory and math is to study - test - pass. Building on what you know.

2. No Classes and No labs! I don't know for sure but I'd be shocked if those or you with college educations in electronics didn't have classes with required labs where you did demonstrations and experiments of the class materials.

3. I think there is vastly more info available on tubes than there was 15 years ago and in this tiny niche tube knowledge and theory has expanded via the net. Yet this information is not in the form of an accepted textbook, standardized nomenclature or an accepted method of evaluation / investigation.

Instead, have various authorities and resources who are largely self qualified and often contentious with each other. As soon as we say we've learned something from Gerald Weber or Kevin O'Connor we or they are attacked often personally as well as "professionally"

It makes it very hard to learn the information in a confident way.

Eric

[KT66]

MCRacer, I hear what you are saying. We all meed to rant a little sometimes, and I think this was prompted by a recent post by a young man who knows nothing, but wants to know how to make the ultimate do everything amp. We see these kinds of posts from time to time, and although they are somewhat naive in their ignorance, I think it's exciting when a young person is seeking knowledge about anything these days. I wouldn't worry that we never hear from many of them again - I think some lose interest and decide against it, some start out on their journey and just don't report back.

As long as you understand the safety issues, I think paint by numbers is a good way to do things. Working from a known good layout is one of the key things I recommend to newbs to ensure a successful build. When I was a lad my dad and I put together a number of Radio Shack projects and I have no idea how a shortwave radio receiver works, for example, but it still was cool when we followed all the directions and ended up with a working unit.

This little club we have here at TAG is very special. Our membership ranges from some of the most premier boutique builders to complete novices, and all the rest of us somewhere in between. As Mark expressed, I feel indebted to all those here and elsewhere on the web who I learned from, so I try to contribute when I feel that I have something to offer - which isn't all that often because you guys are all so smart !

[jimsz]

I don't know if it is just me but it gets a little aggravating or maybe just frustrating that the number of guys who don't have a clue trying to build rather complicated amps.

Guilty.

I am exactly one of those guys. I bought a Weber kit that was way above my level of understanding. It took a good 6 months to build and another 6 months of troubleshooting, but now it works great.

I really didn't want to get into amp building the way I did. It was a co-worker of mine who convinced me to do it. He is an electronics genius, you know, the kind of guy that contributes to electronics textbooks, that digs around in a pile of electronics parts that have been tossed out and builds something from a drawing he made on a paper napkin.

Of course, he told me about the dangers of amp building, but that information is on most websites, it was made explicitly clear on the Weber website where I bought my kit.

He then went on to say that although the build was complicated, I could make it as long as I followed the layout and understood the schematic. It was the troubleshooting skills I did not possess that had me stumped when certain circuits did not work properly. It was the fear of the unknown that made troubleshooting quite an overwhelming concept to deal with, but he said it was just a matter of going over the build to eventually discover the problem and fix it.

"Everything can be fixed," he said. "No problem."

Did this amp build give me an equivalent understanding compared with most folks here? Not a chance. But, after a year of working on it, I have come to understand a great deal more about tubes and electronics.

Of course, I also spent the time going over free online courses, like this one: http://www.electronicstheory.com/ which helped tremendously in understanding the components and some of the math.

If I did aggravate or frustrate anyone here, I do apologize, it was certainly never my intention. The only thing I wanted to do was learn how to build an amp and learn about electronics. The unfortunate part about this is that there just wasn't anyone around that would take the time to do it. They all refused as they were too busy.

All I could do was turn to the internet for help.

[Phil_S]

All I could do was turn to the internet for help.

I think this really sums it up. Tubes aren't taught any more. I believe, however, the OP's real complaint was about the poor attitude we sometimes encounter.

[mcrracer]

A great big Congrats, Jimsz, on your success. I want to see more of the younger guys come in and carry the torch so to speak. Just safely. I know I wont be here forever. I understand about not having someone to help because I did have someone who started me and insisted that I learn schematics and what the parts did before I made my first solder joint. As a matter of fact my first build was a crystal radio set...NO voltage . And he took me from there step by step learning as I went. Then joined the Air Force and got in depth training in electronics including tubes. I consider myself lucky to have learned as I did. I am more than willing to help new guys get started and progress.

[jimsz]

I think part of the problem of not having so many others to support us newbies is the fact that the business of electronics build and repair has literally gone out the window with the advent of the latest electronic technology. There just isn't really a market for people to teach and learn as there was in the past. It seems one of the only ways to learn is to do a DIY project like a guitar amp kit.

If any local schools or businesses offered up courses on amp building or other related products, I'd have been first in line.

[paulster]

All I could do was turn to the internet for help.

I think this really sums it up. Tubes aren't taught any more. I believe, however, the OP's real complaint was about the poor attitude we sometimes encounter.

Exactly.

Anyone can build an amp if they approach it with the right attitude and understand (and are prepared for) the complexity of the particular build they're taking on.

It's when attitude doesn't equal expectation that it can get a bit frustrating. For all concerned!

[jaysg]

EE here. I commiserate with the OP, but ime, building amps is a mechanical effort. The electronics side isn't as important as knowing how to build things in general. Designing amps...not a lot of new designs out there, however, I will admit my own take is a trap. I screwed something up on my Liverpool simply because I was trying mods people suggested and I didn't take 2 seconds to ponder what changing an RC constant does.

In my case, I'm often so pleased with the first results of a new build -- amp or pedal, that my curiosity disengages quickly. This why guys like Bob Reinhardt sells amps and I don't. He's listening for more and wants more from the experience.

[David Root]

You don't have to have Radiotron Designer's Handbook 4th edition in your head, but you do have to learn the basics.

In my learning experience I found that most of the literature does not distinguish clearly enough or early enough at the basic learning level between the DC and AC structures, let alone how they interrelate. Interstage impedance issues were not properly addressed either. This confused me considerably early on.

I have personally used a conceptual construct that the DC structure is like the human body's skeleton, and the AC structure and dynamics are the muscles informed by the mind(=guitar signal). Yes it's an oversimplification but it does work as a useful guide I think. Worked for me anyway.

Still haven't quite figured out where interstage impedance fits in this schema, opinions welcome! Loading and resistance to effort probably, but this is where analogies start to break down I think.

[Richie]

Very good thread.I've tried to pass on the things i know or have found out over the years and help others learning. I've been on many amp forums through the years.
And i have learned as much from others as i have helped others. I've seen some guys start out very novice,but now own amp companies. Started on Ampage,it that time it was the best place to be. Helpful guys and laid back. Then Helped out the start of 18watt.com
And met so many friends there.
Their is so much info out there now for people wanting to learn. Usually if they build one amp,they will get hooked and build others.
The forums are great places to hang out and learn and get help along the way.
I do understand the post. In the many years of helping, i have probably about seen it all. Some first time builders build an amp that looks as good as any. Then you see as bad as it can be.
We would have people post pics to help see what the problem was. Some, you would not have any answer. So bad that you didn't know what to say to them.
If they couldn't look at the colored layout,and all the posted pics, and get similar,then they shouldn't be building.
The things that bugged me is when you tried to help,or make a suggestion,and the person that knows nothing would say.. "I don't think that could be the problem"
And not even try your suggestion. Or 3 other gurus would lead them off to some other directions.
But really i've only seen about 3 or 4 that nothing you could do or say would help. Those should just lay down the soldering iron and step away.
The other thing for the new amp builders.
Some people are very nice. Others come in and think your supposed to be at the keyboard ready to answer every question.

And they don't or won't look for info. And may never say thanks for helping them.
A first build amp,if it turns out with no problems,thats cool. But one that has problems,you learn something when you get help in fixing it.
And the last thing, when looking for info or being in a forum,many may not know the amount of "free" time it took to compile the info and have it for everyone to just come in and use it to paint by numbers.
If it wasn't for those helping,sharing and working together it would not be there.
And if you get help, a thank you will go a long way.

[Cliff Schecht]

You don't have to have Radiotron Designer's Handbook 4th edition in your head, but you do have to learn the basics.

In my learning experience I found that most of the literature does not distinguish clearly enough or early enough at the basic learning level between the DC and AC structures, let alone how they interrelate. Interstage impedance issues were not properly addressed either. This confused me considerably early on.

I have personally used a conceptual construct that the DC structure is like the human body's skeleton, and the AC structure and dynamics are the muscles informed by the mind(=guitar signal). Yes it's an oversimplification but it does work as a useful guide I think. Worked for me anyway.

Still haven't quite figured out where interstage impedance fits in this schema, opinions welcome! Loading and resistance to effort probably, but this is where analogies start to break down I think.

The easiest way to look at AC/DC, at least for what we do, is to look at the grid and plate of a tube and the signals that they operate around. The gate gets a static DC voltage of say 10V. This is a set number that doesn't move at all (or shouldn't). The incoming AC, on the other hand, can be treated as a small wiggling DC signal, usually with a periodicity attached as well (i.e. repeats every 2*pi). DC sets the operating point and AC wiggles this operating point around in order to manipulate the plate current and develop an output voltage. The plate has a big DC signal, say 100V, and a much larger wiggle that is a function of the output current and the plate signal. I guess the big point is to realize that AC is just a wiggling DC signal. The shape and size of the wiggles determines your frequency information contained in the signal. This too is oversimplified (we never mentioned current!) but it's a good way of understanding the mechanics of AC/DC.

It's also good to know that current moves opposite the direction of voltage and that electrons move with the voltage. This is CRITICAL in truly understanding tubes. It's a goofy way to picture things but it makes sense when you look at the flow of energy in a tube. It's all really just convention but it makes sense if you picture electrons flying towards the plate while the current flows towards the cathode. Another way of looking at it is as the potential between the grid and cathode decreases, more electrons are allowed to flow from cathode to plate and more current can flow through the plate which in turn develops a higher output voltage.

A tube (or any transconductance device) is really being used as a controlled variable resistance (plate to cathode is your resistor), with the grid(s) being your control element. The plate resistor is seen as being in parallel with the plate resistance and this forms a sort of voltage divider where the bottom element of the divider varies as the output voltage varies. This literally is like turning a pot to change an output voltage, except these are active devices with a considerable amount of current gain.

Understanding how impedances play against each other is also really important in fully understanding ANY electrical system. In audio frequency designs, we typically aim for the highest transfer of voltage. Compare this to RF where everything is matched to 50 Ohms (or whatever you choose) for the maximum transfer of power from device to device. So we differ in that we are using our devices mainly for voltage gain (talkin preamps here), not current gain. Ideally to get the max voltage transfer from circuit A to circuit B, A has to have the lowest output impedance possible while B has to have the biggest input impedance possible. Low impedances love to drive high impedances, the high impedance stage has NO loading effect on the previous stage and the signal flows nice and easy. You can treat the source-->load relationship as a voltage divider, where the higher the output impedance and lower the input impedance is, the more attenuation you get through the voltage divider. That's why source/load configurations are literally modeled as voltage dividers.

As far as how impedances play against each other, it's actually pretty easy. Let's take a standard gain stage with plate resistor Rp, grid resistor Rg and for convenience, we'll tie the cathode to ground. The input impedance is set by Rg alone if the previous driving stage has a low enough impedance to not act like a voltage divider. This doesn't hold so true for something like a guitar pickup going into a preamp stage, but this interaction actually does some tone-shaping in itself with the pickups in a guitar. Rp is typically 100k and has a DC blocking cap after it before feeding the next stage (RG2). So what's our actual output impedance at the point where Rp, the tubes internal Rp, the DC blocking cap and the next stage meet? Easy, it's Rp//rp//(Cdc+Rg2) where rp is the internal plate resistance, Cdc is the dc blocking cap and Rg2 is the next stages grid resistor. The actual output impedance of the stage we are looking at can then be found by replacing Cdc with 1/(jwCdc) where j is imaginary and w is the frequency in radians. Since you know all of these parameters, you can use this info to plot out your plate resistance at DC (as well as what it looks like at various frequencies).

Something else that is good to consider with interstage impedance of your typical inverting gain stage is that your roll-off from Cdc to RG2 isn't set simply by 1/(2*pi*Rg2*Cdc). You actually have to calculate the effective impedance from the previous stage as well as the forward looking impedance. This interstage impedance "issue" tends to not cause a lot of problems though because the effective cutoff of the high-pass filter goes down instead of up. The amount it shifts is of course dependent on the previous stages output impedance. This also definitely happens in tonestacks and such if you don't use a cathode follower to drive it. Without the cathode follower with pretty dang low output impedance, you "load down" the next stage and cause the "unwanted" shift in frequency response (although many use this to their advantage).



Something I learned recently is that current noise at the input of an amplifier (units are typically pA/rtHz) gets multiplied by the source resistance. So if you are using a bipolar device input on your low-noise amplifier but you have a high driving impedaance, your LNA's performance is going to go to shit. This isn't a problem in FET and vacuum devices because we treat our stuff as voltage controlled devices with negligible grid/gate current, but this is a problem in bipolar devices where the base current is not negligible. Technically FET's, tubes and BJT's are all charge controlled devices, but it's much simpler to treat them as voltage/current controlled devices at audio frequencies. Not sure if we discussed that here or somewhere else, but this is all definitely cool stuff and what I've spent WAY too much time reading about. Is it bad that I treat my Radiotron Designer Handbook's as bibles?

[sst4270]

Just wanted to chime in here. I rarely check out the Technical Discussion threads.

I'm 43.
7 years ago I was one of the new guys. Very ambitiously I'd decided to build a 2 channel tube amp stereo system from scratch. I'm a mechanical engineer and I design speakers for Polk Audio. As a previous hobby I'd built and sold several very nice pool cues. (Still in use)
I'd build some SS amp stuff as well ala Elliott Sound Products. So I had good soldering skills, woodworking skills, CNC skills, Milling machine, Machine Lathe skills, etc... I must've researched for 8 months before making a single purchase. In the end I did build my pure analog 2 channel system. Turntable from scratch (Ala Terres style, look'em up), Phono Pre & Linestage ala Bottlehead stuff, Dynaco ST-70 clone, Single driver full-range rear loaded horn speakers. I think I spent a total of $1500 for the complete system. (With the exception of the Tonearm $500 and Turntable Motor:$750.

I learned a LOT. Made many mistakes. Learned from them. Researched some more.

Since I also sang in a band at the time I decide to build a guitar amp. My lead guitarist suggested the 5E3. More research... Built it. Learned much more from that experience. Next up... TW Express... Built it. That was all in the first year. Since then I've built and sold maybe a dozen amps for fun. (some of which I posted here at TAG) All but one are still being used regularly. (The one is a D'Lite 22 clone that I've never been happy with how it sounded so I won't let it out of the house.)

I never stop researching circuits, forums, gut shots, etc... I've read Merlin's Book, All the Pentode Press books, all the TUT series, RCA radiotron handbook, and several more that I'll probably never open again.

So what was my point...? Oh yeah. first thanks for all the help and advice you guys have given me over the years. [Bows out of respect]

Second, I think that some new builders are un-prepared skill wise or knowledge wise or otherwise for what's entailed in building something like a Dumble or TW. While that's partly their fault because the information and recommendations are certainly available (to go build something simple FIRST) The forum is also somewhat responsible for the newbie's courage (blind or not) by posting such good layouts, schematics, notes, etc... How about that Express Builder's Guide? I mean it really doesn't get much easier than that, does it? When that thing got published I thought to myself, Whoah, TAG really has reached a new level.
The wealth of information on just this forum alone is astonishing.

I had twins last year and shoulder surger in September, but I've still been continuing to build (Because I've really got the bug now) and now I've even been designing. Trying to design anyways.

So finally after all this. Just last week I was working on a simple preamp that I'd designed onto a PCB. Everything on one 4"x5" board including power supply and small toroidal transformer. I'd fired it up and it worked but I needed to solder a jumper lead that I'd missed onto the board. So I grabbed the board to pull out the tubes and ZAP. I got hit with about 350V DC. It left a pinhole blister on my finger and the pain when it hit my shoulder (remember the surgery) felt like someone had just hit me with a baseball bat. I didn't design in draining resistors for the power filter caps because I was following some generic power supply (amp-by-numbers so to speak). Fortunately the pain subsided in about 15 mintues and the only damage was my pride.

While I'm certainly not nearly as experienced as many of you here I feel very confident after 8 years in my ability to build and understand what I'm doing now. Yet I (we) all will continue to make mistakes. We are never too young to continue to learn. After all, isn't that why even the experienced builders hang out here?

Thanks again,

Steve