Amp techs and tinkerers: where do I get started?

Discussion in 'The Workbench' started by GuitarIV, Mar 26, 2020 at 6:39 PM.

  1. GuitarIV

    GuitarIV Well-Known Member

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    So this whole Corona thing freed up a lot of my time.

    I enjoy being able to finally play guitar a lot more, every day, practice, get better.

    At heart however, I am a tinkerer. I am fascinated by gear. I learned to solder, mod my own guitars, do setups, the whole shabang.


    Amps have always been something I was too afraid to tackle. I respect electricity, I respect voltage. You fuck up the wiring in your guitar: no harm no foul. You open up the cavity again and redo the connections; you fuck up in an amp, you might die or set something on fire.

    Now my JCM 800 either needs some new tubes, or possibly a resistor drifted and the bias is off, one of the 4 valves is exhibiting some red plating. I already had my amp tech over, we talked about what needs to be done, however now that we're in quarantine I wanna use the time to learn this stuff, so I can delve into the world of tube amp circuits, how to service, how to repair, how to mod, build my own.


    Now I am sure I have to watch a few Youtube videos to make sure I am 100% spot on with soldering, stuff like desoldering wire, suction pumps etc., that's something that is easily done, I'd still be thankful for pointers; I own a soldering station

    I have a Voltcraft Multimeter, do I need to upgrade? Any insight on that would be great as well.

    I am a person that wants to understand basics; why does something work the way it does? I have material to learn about voltage, current, etc. the physics behind the stuff; but I wanna know why an amp is built the way it is and what happens with the signal that comes out of your guitar when it enters the input jack; what does every part of the circuit do? How does the transformer convert the voltage etc.

    I wanna learn how to read diagrams, how to study schematics, know what's happening and why.

    I have some old tube radios in my basement, should I start there?


    Basically I am looking for help here from all the experienced guys. @ampmadscientist @MickeyJ @NewReligion

    How did you start? What would you recommend I check out first? Any books, online material, Youtube videos?


    I am a bit clueless as it's too much to digest all at once, but I am open minded and ready to learn.

    Hell, I wanna be able to build a 2203 kit start to finish and then add the mods I have in my head myself :)


    Any help is appreciated!

    Stay healthy and safe,


    Cheers
     
  2. ampmadscientist

    ampmadscientist Well-Known Member

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    I think there are some videos on amp building. Learning how to solder is a big +.

     
    Last edited: Mar 26, 2020 at 6:57 PM
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  3. MickeyJ

    MickeyJ Well-Known Member

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    you can start with your bias problem.

    bias supply is a bit tricky, because it twists and turns, and the terms the people use are..almost ridiculously illogical.

    However, if you persevere, the bias 'thing' will become clear to you

    terms like cathode, current and voltage are used.

    there is an amazing word picture someone came here with involving a vacuum cleaner...seek out that word picture.

    In your journey, try not to match the words people are using to what is going on, because the words are illiogical mostly ... think of what's going on as a sequence of videos, or images that you can see in your mind.

    Current is an illogical word on its own...but when you think of water pissing out of a hole in a dam wall, and then just trickling out, from the same size hole...suddenly current means something.

    Look for these word pictures, to me, it all becomes clear with those.

    Look at power supplies first.

    Ac converted to dc with rectifier diodes and a capacitor...wtf is that again?

    but when you break it down, its real easy to understand.

    just one thing at a time.

    Ac waves going from left to right up and down. they meet diodes which chop one half off...so it's just the top half now going from left to right...add a filter capacitor to smooth the line at the very top, the bumpy one, and bam...you have it in your head forever...rectified DC voltage.

    Start at power supplies is my advice.

    wtf is a transformer?

    wtf is AC?

    wtf is DC?

    wtf is transconductance?

    check it all out, and it will all form in your mind.

    be careful what people type out, a lot of it is simply spurious advice..well meaning but simply repeated errors.

    look for the truth in between the lines, filter what you read.
     
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  4. MickeyJ

    MickeyJ Well-Known Member

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    I believe everything you're after is either on or between uncle dougs youtube videos, and rob robinettes web pages.
     
  5. Guitar-Rocker

    Guitar-Rocker Well-Known Member

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    Your red plating could be tube failing, bias issues, or screen resistor for starters.
     
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  6. Nik Henville

    Nik Henville Well-Known Member Premium Member

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    College, or apprenticeship. In my case... both.

    :hippie::pirate::uk:
     
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  7. Filipe Soares

    Filipe Soares Well-Known Member

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    Same here, following.
     
  8. marco_giampa23

    marco_giampa23 Active Member

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    Im in the same boat, uncle dougs videos are pretty good on youtube for explaining how amps work. Just do some googling on how to understand a schematic there is heaps of stuf out there, familiarise yourself of what each part of a schematic is so it is easier to understand how it works
     
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  9. SmokeyDopey

    SmokeyDopey Well-Known Member VIP Member

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    Uncle Doug in youtube. Highly recommended.
     
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  10. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Start with DC electronics. Ohm's Law, Thevenin's Theorem. Volts, Ohm, Amps, Watts.

    Then AC electronics. Inductance, capacitance, inductive reactance, capacitive reactance. AC circuit theory, RC, LC, RLC circuits. Impedance.

    Then tube theory. (And then, semiconductor theory, too.) Rectification, diodes, triode amplification, tetrodes, pentodes. Semiconductor diodes and transistors
    and the ways to use them.

    This is called basic electronics. This makes it SO much easier to know what's what and how it works.

    Learning electronics along this course path will shave YEARS off the time it would take you to acquire equivalent knowledge by experimentation without the academic learning that will give it to you in an orderly manner.

    So put down the soldering iron. Don't look at your parts stash.

    Crack the books or get online courses. LEARN ELECTRONICS and THEN start figuring out how amps work and if you can make your own.

    If you can look at the schematic for a simple amp like a Fender Champ, and can point at EVERY component in the circuit and can tell me what it does and how it does it and why it's there, and what would happen if it were changed in value, or removed, then at that point you will have the basic grounding in electronics that you MUST have in order to make sense of amp design.

    Until you can do that, you're not ready.
     
  11. MickeyJ

    MickeyJ Well-Known Member

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    if he can point at every component and do so, then he has already made sense of amp design, silly post matthewsguitars.
     
  12. ampmadscientist

    ampmadscientist Well-Known Member

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    How did you start?

    The label said: "no user serviceable parts inside."

    I just ignored that, and did it anyway.

    Recklessly opening up tube equipment and shocking myself.
    Eventually I learned not to shock myself. :lol::lol::lol:

    Oh yeah, getting shocked is part of the experience.
    If you are the type who whines and cries over a few hundred volts, you shouldn't be working on tube amps.
     
  13. MickeyJ

    MickeyJ Well-Known Member

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    NewReligion, this guy...you know the dark room with the swirling smoke, the whispers..the shadows..the colors appearing then disappearing..This is where NewReligion is, he is beyond the science of it, this guy...he lives in the world of sweet, sweet tone.
    Pls note, tone is far from schematics, very, very far from it.
     
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  14. ricksdisconnected

    ricksdisconnected Well-Known Member

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  15. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Second vote to build a tweed Champ. If you haven’t been yet, check out all the kits at Mojotone.com. They use good quality parts.
     
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  16. Wenander

    Wenander Active Member

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    start with learning basic electronics, ohms lawthe other dude´s name´s law .... and reading schematics! because most amp kits come WITHOUT a step by step guide (wich basically would make it grown up´s LEGO)

    so reading schematics is important to say the least
     
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  17. Nik Henville

    Nik Henville Well-Known Member Premium Member

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    Not so - from tone stacks to input circuits to power amp and feedback loops...
    ...the schematic can, sometimes, be the key to tone. Ignore it and work blind by all means :cool:

    :hippie::pirate::uk:
     
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  18. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Tone is frequency response. Component values dictate frequency response. Applying the appropriate mathematical formulas will tell you what's what and how to change it to be what you want it to be.
     
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  19. AlvisX

    AlvisX Well-Known Member

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    Yeah ,that's it ,keeping an eye on where your body is in relationship to the equipment and GROUND ...or as they say in England ,"Urth" (Earth)

    Remember.....it's the CURRENT that kills ya ! Don't become the circuit
     
  20. NewReligion

    NewReligion Well-Known Member VIP Member

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    IMO (And thank you for the great words gentlemen) once you have read and understand enough to be SAFE and confident, then proceed.

    I started by purchasing a early 90's reissue Plexi model 1987X with no loop.

    I then carefully measured for the mounting holes and drilled. Followed instructions from George Metropoulus. Good deal, all was well as it worked perfect.

    I then bought a turret board and populated it. (Ensure it will provide the proper placement for components and connection points (Though many can be done later in your evolution as point to point off of sockets etc...). I pulled the PCB and installed the turret board in order to easily replace brands and values of components like lego's to better understand with my own ears what "I" preferred.

    This amp went from a stock Plexi to a crying high gain amp. Pick the brains of individuals with alluring questions they can not resist. Along the way many will help you down the path so long as you are SAFE and humble.

    I have had a few mentor me but Guitar-Rocker took me on to teach me the important lesson's. Thank you Terry! To this day if I have a question I call and we discuss the issue at hand...Very very smart out of the box critical thinker.

    I delve into the high gain world where you will find a lot of disinformation and deception. I do not intend to sound negative but it is just a fact you should be aware of.

    My point is look for those you may trust.

    Remember Safety Safety Safety. Always drain your caps. So buy a 100k 5 watt or 10 watt fire proof ceramic filled wirewound resistor to drain the caps so the amp is safe. You will also need insulated 2 alligator clips and wire.

    You will at some point get your cherry popped when you accidentally hit DC or AC. It IS going to happen so please take your time think about everything you do when the power is on and the circuit is exposed and even when not. Drain that SOB.

    I suggest buying a nice Fluke meter and a couple Wal-Mart junkers for other applications and a nice soldering station.

    Be SAFE and have fun.

    Thanks again Guitar-Rocker!

    David a.k.a. New Religion.
     
    Last edited: Mar 27, 2020 at 10:55 AM

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