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Thread: AmpClones.com Mesa Boogie Mark IIC+ Help total newb

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    Member WesPalladini's Avatar
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    AmpClones.com Mesa Boogie Mark IIC+ Help total newb

    Hello.

    My dream amp (right now) is a mesa boogie mark IIC+. I was tired of constantly getting out bid on e bay for one, then waiting months for another to appear. If I won and wanted to send it to Mike B at mesa for a mod/upgrade it is even harder because he said if it comes from the states they can only ship it out once they upgrade it to someone in the states, (I live in Canada). So that means I would have to get it shipped to me then ship it to Mike then him ship it back, such a mess. So I decided to give a shot at making one.

    I ordered the chasis and the PCB from MARK 2C+ Chassis + Complete PCB set - $155.00 : AMPCLONES.COM, Tube guitar amplifier PCB boards, chassis, transformers and DIY kits
    It came with 3 boards, and 6 pages of schematics. FML this is not as easy as lego, nor as safe.

    1) So I thought my first step should be to take a picture of each PCB, start writing down every component I need to buy and how many and open the picture up in paint and scratch off that component as I go.
    2) So I am trying to match the boards with the schematics, I believe I have found the board and schematics that are responsible for the Graphics EQ but have some questions:

    I noticed it says 60Hz on the schematic but the equalizer on the boogie is 80Hz (Small issue for the most part, I think)
    RV8 to RV12, does RV mean Variable Resistor (Pot)?, if so why do they call it RV instead of VR?
    are all of those pots supposed to be 50k Ohms?
    How do you call a pot like this that is not round but supposed to be vertical, and where can I buy some?
    Is the pot supposed to fit between position 1 and 2 after the 470 and 1k resistors or in each pair of spots labelled 3?
    How do those 3 holes at the bottom left of the board match up with the schematic?

    Any help would be EXTREMELY appreciated, I think I am in over my head and will need a lot of walking through this, I thought amp clones would have included a lot more detailed instructions.

    THANKS!!!
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    Lets see, capacitors and coils affects the resistance in a circuit. The resistance varys over different frequencys. So the eq has coil+cap connection to get a frequency band. The 5 controls are there so that you can vary how much of the frequency band will get through to the next stage.

    The eq-controls, you posted a picture. Isn't that your picture..? The 5 controls seems to be mounted already.

    By the way. I like your spirit - jump in the deep end! Just don't underestimate the voltages you're going to mess around with.

    Edit. I just had an other look on your picture. The switch is to stop the signal to ground dump. In other words, a switch that works as an on/off to the eq.

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    Don't forget the joker g1's Avatar
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    Have you contacted them and asked if there is more info/instructions available? That should be your first step.
    Yes you are in way over your head. Not impossible but it's going to take a LOT of time and money. Have you priced out transformers? I don't think there will be much room in there, you will need something very close in size or exact replacements if you don't want to redrill the chassis mounting holes. You should look into transformers before you go much further.
    Once it's all built, the routing of the wires (lead dress) will be critical. It may take a long time to work out wiring issues.
    Sorry to sound scary, but you need a realistic idea of what you are up against.
    Quote Originally Posted by WesPalladini View Post
    1) So I thought my first step should be to take a picture of each PCB, start writing down every component I need to buy and how many and open the picture up in paint and scratch off that component as I go.
    This will be the easy part. Again suggest you do more research first so you don't end up with a bunch of stuffed pcb's you can't find/afford hardware for. Also, the schematic does not show wattage for the resistors or voltage ratings for the capacitors. You won't be able to get the right parts without that info.

    Quote Originally Posted by WesPalladini View Post
    2) So I am trying to match the boards with the schematics, I believe I have found the board and schematics that are responsible for the Graphics EQ but have some questions:
    I noticed it says 60Hz on the schematic but the equalizer on the boogie is 80Hz (Small issue for the most part, I think)
    Small issue, maybe even a typo on their schematic. Does the chassis you have say 60 or 80? Is that their schematic? Get the proper mesa schematic and check if that circuit is the same.

    Quote Originally Posted by WesPalladini View Post
    RV8 to RV12, does RV mean Variable Resistor (Pot)?, if so why do they call it RV instead of VR?
    Maybe that's how they do it in Russia?

    Quote Originally Posted by WesPalladini View Post
    are all of those pots supposed to be 50k Ohms?
    Yes, the frequency depends on the cap and the coil, as uberfuzz stated

    Quote Originally Posted by WesPalladini View Post
    How do you call a pot like this that is not round but supposed to be vertical, and where can I buy some?
    They are called slide potentiometers. You will have to find parts suppliers (mouser, digikey etc). Prepare to spend a lot of time looking for parts. Google is your friend.

    Quote Originally Posted by WesPalladini View Post
    Is the pot supposed to fit between position 1 and 2 after the 470 and 1k resistors or in each pair of spots labelled 3?
    The slide pots will have 2 legs at one end that go in 1 & 2, the other end will have a leg that fits in #3. The middle hole #3 is probably optional.

    Quote Originally Posted by WesPalladini View Post
    How do those 3 holes at the bottom left of the board match up with the schematic?
    The schematic is showing a bit more than the eq board. Some of the parts on that schematic (LDR5 and the upper half of schematic) are probably on the main board. One hole goes to pin 3 of LDR5, one hole to the ? you drew lower left, one hole the the ? you drew at Q3.

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    Member WesPalladini's Avatar
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    Quote Originally Posted by überfuzz View Post
    Lets see, capacitors and coils affects the resistance in a circuit. The resistance varys over different frequencys. So the eq has coil+cap connection to get a frequency band. The 5 controls are there so that you can vary how much of the frequency band will get through to the next stage.

    The eq-controls, you posted a picture. Isn't that your picture..? The 5 controls seems to be mounted already.

    By the way. I like your spirit - jump in the deep end! Just don't underestimate the voltages you're going to mess around with.

    Edit. I just had an other look on your picture. The switch is to stop the signal to ground dump. In other words, a switch that works as an on/off to the eq.
    No the controls are not mounted yet, I just google searched an image of the Mark IIC+ then cropped the graphics EQ part and pasted it in this picture to give people a better idea of what I am talking about.

    Yes high voltage stuff is what I am worried about, any tips on staying safe?

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    Safety... Well I guess the best thing to do are some google searches.
    In short
    • Always one hand on the back while you're got the amp fired up.
    • Make sure you know how to drain the filter caps on your amp and why you need to do it. (They hold juice even if the amp is turned of or un plugged.))
    • Measure from ground to point. A simple subtraction is safer than point to point measurements.
    • Always triple check every thing. (Might save other things than your life.) ;-)


    Edit, no point in reanswering questions answered by g-one.

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    Last edited by überfuzz; 11-08-2011 at 05:58 PM.
    In this forum everyone is entitled to my opinion.

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    Old Timer tedmich's Avatar
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    you'll really need an accurate "Bill of Materials" (BOM) to build this up, as the PCB is designed with very specific parts, ie the spacing of the lead pins on the linear pot will only work with the pot it was designed for. Did they send a BOM? You can even build up a BOM at Mouser if you register and then buy parts as you can afford them.

    Putting parts on the PCB is a no brainer, just be sure that orientation is observed for EL caps (+/-) and any transistors LDRs etc as there is only one right way to mount them. Lead dress/running wires between the PCBs is where it can all go south for a high gain amp, take your time and totally mimic some of the beautiful build's documented at sloclone and the sloclone/smashguitars commercial sites.
    Soldano SLO100 Log


    If ampclones has an online build guide/photo diary this would be PERFECT, even if its in russian its the pictures you'll need to copy.

    Nothing bad can happen except:

    -electrocute/kill yourself, burn down house
    -very noisy amp which drives you nuts

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    Member WesPalladini's Avatar
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    Thank you for your comments so far.

    I have e mailed them to see if they have a BOM or a picture journal. Also I am still waiting for the chasis and I just got my new soldering iron !

    I am just thinking that there must be a good book/text book that I should purchase to teach myself more about this field. Any suggestions?

    It would be cool if there were a few dedicated people to help guide me through this, I would post videos/pictures to make a journal for future builders.

    -WP

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    Old Timer tedmich's Avatar
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    the build guide I posted is a good study, and there are MANY online, for intros to tubes
    try here:
    Technical books online
    (the Crowhurst books are great)


    For guitar amps try Merlin's web site,
    How to design valve guitar amplifiers
    some of it is down ;(

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    keep in mind that the mark IIc+ is a bit more complicated then the slo.

    well a lot more complicated actually.

    that being said the parts themselves should be all available on mouser or something like it.

    The inductors for the eq and the slide pots are probably going to be the most expensive.

    Other then that take a look at some MarksII's to get an idea of what you are getting into.


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    Are you absolute sure you'll pull this off..? I'm not a pro builder, more like average, this scheme seems kind of gnarly.

    This forum has more than a "few dedicated people" eager to help. So if you think you can land this jumbo jet by instructions. Go for it dude! My first build was a Twin Reverb and I loved every bit of it. Eh now I love playing/listening to it.

    Keep us nerds updated. :-)

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    ToneOholic! big_teee's Avatar
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    Quote Originally Posted by überfuzz View Post
    Are you absolute sure you'll pull this off..? I'm not a pro builder, more like average, this scheme seems kind of gnarly.

    This forum has more than a "few dedicated people" eager to help. So if you think you can land this jumbo jet by instructions. Go for it dude! My first build was a Twin Reverb and I loved every bit of it. Eh now I love playing/listening to it.

    Keep us nerds updated. :-)
    Hi, and best of Luck:
    I'm a 40 year Communication Tech, and I just built from scratch my JCM800 2204 Marshall Clone.
    It was plenty tough for me, Your Project is way over my Head.
    If I were You, I would put that thing in the closet.
    Build some lesser Kits, and get the skill and confidence up.
    That way you could learn some practical amp experience, with the transformers, and Cap discharging Procedures.
    Don't mean to scare or discourage you, but looks like a Heavy chore for Sure.
    Good Luck,
    Terry

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    Terry

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    Supporting Member Corona Blue's Avatar
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    Quote Originally Posted by überfuzz View Post
    The switch is to stop the signal to ground dump. In other words, a switch that works as an on/off to the eq.
    This is correct. But there is more. The original switch for the EQ was a 3 position switch that was setup this way:

    UP = EQ on

    MID: IF channel = "Rhythm" THEN off. ELSE, on.

    Down = EQ off

    So the lead channel switch also closed the circuit for the EQ when the EQ switch was in the MID position. This is where I leave mine most of the time, although with some guitars, I will switch the Graphic out completely.

    As if that wasn't enough, there was also an auxiliary footswitch box available to switch the reverb or the graphic in or out. On the originals, there was a stereo phone jack up under the chassis pan, just to the right of the speaker (looking from the back). It's a pain in the butt to reach around all the tubes to plug it in, but it is great to be able to control these features with the footswitch.

    Mine is a December of 1983 Mk II C Simul (Reverb, EV12L, hardwood combo) that was upgraded to a C+ a few months later by the Mesa techs. I ordered and picked it up directly from the factory as I lived in the SF Bay Area at that time.

    I agree with what Big_Tee says... it's a huge undertaking to build one of these for a first amp build. Finding transformers that will operate and sound like the originals will be very challenging as well. The OT's on these amps were designed to run specifically around the performance parameters of the Sylvania STR-415 power tubes. You can use other tubes, and some will sound pretty good. But the unique character of these amps was, in my experience, largely found in that combination of the OT and the 415's. I pass that along just as anecdotal info.

    There must be other builders who have built this kit before. What kind of information are you getting from them about things like proper trannies and inductors?

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    Old Timer soundguruman's Avatar
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    Well, the design is very complicated and it's not for a beginner. You will probably wind up taking it to a tech and spending a lot of money to make it work.

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    Hi, i have a mesa mark III and i was going to copy the eq and untilize it in a different amp. If you'r having trouble finding inducers take a look at futurlec. I haven't personally had any expierience ordering from them but i have heard that they'r a little slow if your in a hurry but they should be reliable at least as far as i know.

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    Member WesPalladini's Avatar
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    Thank you

    Just wanted to say thank you to everyone who has posted so far. I am going to post the schematics they gave me so you can all see. And respond to all your comments later today just had a lot of school due for university in the past few weeks.

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    Member WesPalladini's Avatar
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    Quote Originally Posted by überfuzz View Post
    Are you absolute sure you'll pull this off..? I'm not a pro builder, more like average, this scheme seems kind of gnarly.

    This forum has more than a "few dedicated people" eager to help. So if you think you can land this jumbo jet by instructions. Go for it dude! My first build was a Twin Reverb and I loved every bit of it. Eh now I love playing/listening to it.

    Keep us nerds updated. :-)
    I am I sure I can pull this off? Yes, alone will take a long time. But yes I think I can land it with instructions from home base.

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    Member WesPalladini's Avatar
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    Quote Originally Posted by überfuzz View Post
    Safety... Well I guess the best thing to do are some google searches.
    In short
    • Always one hand on the back while you're got the amp fired up.
    • Make sure you know how to drain the filter caps on your amp and why you need to do it. (They hold juice even if the amp is turned of or un plugged.))
    • Measure from ground to point. A simple subtraction is safer than point to point measurements.
    • Always triple check every thing. (Might save other things than your life.) ;-)


    Edit, no point in reanswering questions answered by g-one.
    Yea so they said no BOM and no picture/video diary. They felt it was quite easy to build based on the schematics. I guess they didn't plan on making this easy for the average DIYer. They said I could ask them 1 question at a time.....

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    Member WesPalladini's Avatar
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    Quote Originally Posted by Corona Blue View Post
    This is correct. But there is more. The original switch for the EQ was a 3 position switch that was setup this way:

    UP = EQ on

    MID: IF channel = "Rhythm" THEN off. ELSE, on.

    Down = EQ off

    So the lead channel switch also closed the circuit for the EQ when the EQ switch was in the MID position. This is where I leave mine most of the time, although with some guitars, I will switch the Graphic out completely.

    As if that wasn't enough, there was also an auxiliary footswitch box available to switch the reverb or the graphic in or out. On the originals, there was a stereo phone jack up under the chassis pan, just to the right of the speaker (looking from the back). It's a pain in the butt to reach around all the tubes to plug it in, but it is great to be able to control these features with the footswitch.

    Mine is a December of 1983 Mk II C Simul (Reverb, EV12L, hardwood combo) that was upgraded to a C+ a few months later by the Mesa techs. I ordered and picked it up directly from the factory as I lived in the SF Bay Area at that time.

    I agree with what Big_Tee says... it's a huge undertaking to build one of these for a first amp build. Finding transformers that will operate and sound like the originals will be very challenging as well. The OT's on these amps were designed to run specifically around the performance parameters of the Sylvania STR-415 power tubes. You can use other tubes, and some will sound pretty good. But the unique character of these amps was, in my experience, largely found in that combination of the OT and the 415's. I pass that along just as anecdotal info.

    There must be other builders who have built this kit before. What kind of information are you getting from them about things like proper trannies and inductors?
    Interesting I didn't know the EQ worked that way. Also didn't know the originals had the jack on the back, this one has the jack mounted on the front .

    I havn't found any other builders of this kit, I have been looking and was hoping one would happen to see my post and help out but no luck yet.

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    Old Timer tedmich's Avatar
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    Quote Originally Posted by WesPalladini View Post
    Just wanted to say thank you to everyone who has posted so far. I am going to post the schematics they gave me so you can all see. And respond to all your comments later today just had a lot of school due for university in the past few weeks.
    Gr8! Most of the online Mesa schematics are famously "nonfunctional" to keep down the clones and are only useful for repairs. The only "deal breaker" on the BOM would be the spacing on the pots IMO at least there are only a few sources for linears...

    I don't know why so many are freaked by how "complex" this is, if its a correct schematic with a correct PCB you can build it up no problemo; its NOT rocket science! The only "problemo" is if a mistake was made on their end or your end! "Troubleshooting" is MUCH more of an art than assembly IMHO...


    Hell scan the boards and I'll build up a BOM at Mouser...maybe!

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    Member WesPalladini's Avatar
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    Quote Originally Posted by tedmich View Post
    Gr8! Most of the online Mesa schematics are famously "nonfunctional" to keep down the clones and are only useful for repairs. The only "deal breaker" on the BOM would be the spacing on the pots IMO at least there are only a few sources for linears...

    I don't know why so many are freaked by how "complex" this is, if its a correct schematic with a correct PCB you can build it up no problemo; its NOT rocket science! The only "problemo" is if a mistake was made on their end or your end! "Troubleshooting" is MUCH more of an art than assembly IMHO...


    Hell scan the boards and I'll build up a BOM at Mouser...maybe!
    Schematics!
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    Old Timer soundguruman's Avatar
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    Quote Originally Posted by tedmich View Post
    Gr8! Most of the online Mesa schematics are famously "nonfunctional" to keep down the clones and are only useful for repairs. The only "deal breaker" on the BOM would be the spacing on the pots IMO at least there are only a few sources for linears...

    I don't know why so many are freaked by how "complex" this is, if its a correct schematic with a correct PCB you can build it up no problemo; its NOT rocket science! The only "problemo" is if a mistake was made on their end or your end! "Troubleshooting" is MUCH more of an art than assembly IMHO...


    Hell scan the boards and I'll build up a BOM at Mouser...maybe!
    They are complex because too many parts, crammed in too small a space, with much too little space between the circuit tracks, inaccessible maintenance because of a poorly thought out hardware and double sided board design. It's pretty much as if they wanted to discourage people from maintaining it, and that's a success.
    The amp can be copied, but the schematic does not show a great deal of the circuit, or the layout, which at some points is rather critical. There are a number of capacitors, to stop the oscillation and ringing, which are not shown on the schematic. Also the circuit tracks are laid out to act as capacitors and shielding, which is not shown on the schematic.
    So you can build it, but it would take a more experienced person to get the bugs out of it.
    If you do not have a scope and other test equipment, you can pretty much forget about it.

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  22. #22
    Member WesPalladini's Avatar
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    Quote Originally Posted by soundguruman View Post
    They are complex because too many parts, crammed in too small a space, with much too little space between the circuit tracks, inaccessible maintenance because of a poorly thought out hardware and double sided board design. It's pretty much as if they wanted to discourage people from maintaining it, and that's a success.
    The amp can be copied, but the schematic does not show a great deal of the circuit, or the layout, which at some points is rather critical. There are a number of capacitors, to stop the oscillation and ringing, which are not shown on the schematic. Also the circuit tracks are laid out to act as capacitors and shielding, which is not shown on the schematic.
    So you can build it, but it would take a more experienced person to get the bugs out of it.
    If you do not have a scope and other test equipment, you can pretty much forget about it.
    I have a multi meter... they have an electrical engineering class at my university so I am sure I can get access to a oscope when needed.

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    Old Timer tedmich's Avatar
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    popped the schematics into a smallish pdf file
    https://docs.google.com/open?id=0Bx4...JhMTNjMWEwYzUy

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  24. #24
    Member WesPalladini's Avatar
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    Picked up a transformer

    Dmitry at ampclones (where I got the board and PCBs from) I guess happened to be on this forum and saw my post. He gave me a lot of encouragement and actually helped me find a transformer that was meant for this build but the guy never got around starting the project (hope I don't turn out like him). New it cost around $125 I picked it up for $80, just wanted to mention his help on the forum. It is an #HTS-10121 (Heyboer). I will also scan the boards in soon times and upload my BOM so far.

    -Wes

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  25. #25
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    Off topic, slightly...

    Dude, there are some questions that you might consider before you set sail. First of all, what sound are you looking for? There might be some wiz-techs here able to point out a simpler way. Secondly, you're mentioning the BOM list every now and then, but you've already started to order stuff. I'm not sure but I guess the first one mentioning the BOM list did it because it's most likely you'll figure, holy Moly thats even more than the amps going on ebay. (Cheaper builds often gets the hardware from retired amps and such.) Finally, have you seen anyone posting builds on this on the net. Check the tube, it might give you an idea what you're in for.

    I don't want to be discouraging, just thought you might give it a thought,... or two. :-)

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    In this forum everyone is entitled to my opinion.

  26. #26
    Old Timer soundguruman's Avatar
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    Sellers often mislead customers into believing they can build their own amplifiers.
    They tell you that all you need is basic soldering skills.
    Don't believe it. More than often these kits wind up in the hands of professional techs, who finish them the right way.
    If you do not have soldering station, O scope, load bank, sine wave generator, multimeter, and the training and ability to use them all, you are probably fooling yourself.
    Also, the amp you are copying is not what I would call the greatest design. You can bank on spending much more to maintain it than an ordinary amplifier.

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    Old Timer tedmich's Avatar
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    All true but these things go for +$3k, so an initial ~$300 investment and learning/buying on the installment plan can provide tons of "hobby time" and it may sound great in the end.
    Had a friend who rebuilt a '67 Firebird in his garage over the course of 10 years; too bad he couldn't hire a pro but he had a ton of FUN doing it and it cost pennies on the dollar (as his time was "free")

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  28. #28
    Member WesPalladini's Avatar
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    Exactly!

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  29. #29
    ToneOholic! big_teee's Avatar
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    Quote Originally Posted by WesPalladini View Post
    Dmitry at ampclones (where I got the board and PCBs from) I guess happened to be on this forum and saw my post. He gave me a lot of encouragement and actually helped me find a transformer that was meant for this build but the guy never got around starting the project (hope I don't turn out like him). New it cost around $125 I picked it up for $80, just wanted to mention his help on the forum. It is an #HTS-10121 (Heyboer). I will also scan the boards in soon times and upload my BOM so far.

    -Wes
    Don't Mean to be the 1/2 Glass Empty Guy.
    However If Dmitry is reading these Posts, Why doesn't he jump in here and help out.
    Sounds like He's just lurking in the Bushes to continue to sell you stuff?
    B_T

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    "You can't promote principled anti-corruption action without pissing off corrupt people!" Diplomat George Kent
    Terry

  30. #30
    Member WesPalladini's Avatar
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    Quote Originally Posted by big_teee View Post
    Don't Mean to be the 1/2 Glass Empty Guy.
    However If Dmitry is reading these Posts, Why doesn't he jump in here and help out.
    Sounds like He's just lurking in the Bushes to continue to sell you stuff?
    B_T

    He didn't sell me the transformer he just found somebody with a used one in the states for me.

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  31. #31
    ToneOholic! big_teee's Avatar
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    Quote Originally Posted by WesPalladini View Post
    He didn't sell me the transformer he just found somebody with a used one in the states for me.
    Sorry!
    Yes I'm a Skeptic at Heart.
    It goes with the 42 Years in the Telephony Bizz!
    B_T

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    "You can't promote principled anti-corruption action without pissing off corrupt people!" Diplomat George Kent
    Terry

  32. #32
    Old Timer soundguruman's Avatar
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    I would recommend that you start by building several smaller electronics kits, until you develop some familiarity w/ components and soldering.
    Then after that, give the tube amp a try.

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    Member WesPalladini's Avatar
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    PCBs and parts and video question

    Ok so here are close ups of the 3 PCBs and I made a list of parts so I can populate them. Please watch for my question: Here

    CAP BOARD
    Value Type Quantity
    220uF/350V Cap 4

    150k/2W Resistor 2

    1N4007 Diode 4

    0.047uF/1kV Cap 1

    GRAPHICS EQ

    470 Resistor 3
    1K Resistor 2

    0.033uF Cap 1
    0.15uF Cap 1
    0.22uF Cap 1
    0.39uF Cap 1
    3.3uF Cap 1

    1.0H Inductor 1
    0.39H Inductor 1
    0.22H Inductor 1
    0.068H Inductor 1
    0.033H Inductor 1

    50K Slide Pots 5

    MAIN BOARD

    Value Type Quantity
    220uF/63V Cap 2
    47uF/100v Cap 2
    470uF/16V Cap 1

    680K Resistor 2
    470K Resistor 4
    270K Resistor 2
    220K Resistor 6
    150K Resistor 3
    120K Resistor 1
    100K Resistor 1
    91K Resistor 1
    82k Resistor 2
    68K Resistor 1
    56K Resistor 1
    47K Resistor 2
    22K Resistor 4
    15K Resistor 3
    10K Resistor 2
    4K 7 Resistor 1
    3K 3 Resistor 12
    1k 5 Resistor 7
    1k 2W Resistor 3
    10M Resistor 1
    1M Resistor 2
    3M3 Resistor 1
    680 2W Resistor 1

    820 Resistor 1
    470 Resistor 5
    220 Resistor 1
    150 Resistor 3
    100 Resistor 6
    89 Resistor 1

    VALUE??? LDR 5

    10uF/63V Cap 2
    0.002uF Cap 1
    0.22uF Cap 1
    0.47uF Cap 3
    2.2uF Cap 1
    15uF Cap 4
    0.005uF Cap 2

    1nF Cap 1
    22nF Cap 2
    47nF Cap 6
    100nF Cap 5
    100nF 200V Cap 1

    10pF Cap 2
    20pF Cap 1
    47pF Cap 1
    120pF Cap 2
    250pF Cap 2
    500pF Cap 1
    750pF Cap 1
    1000pF Cap 1


    MPSA63 Darlington Transistor 1 Q1
    MPSA20 Darlington Transistor 1 Q2
    MPSA70 Darlington Transistor 1 Q3
    MPSA70 Darlington Transistor 1 Q4
    Click image for larger version. 

Name:	Graphics EQ.JPG 
Views:	241 
Size:	2.48 MB 
ID:	16407Click image for larger version. 

Name:	Cap Board.JPG 
Views:	149 
Size:	2.34 MB 
ID:	16406Click image for larger version. 

Name:	Main Board.jpg 
Views:	414 
Size:	1.45 MB 
ID:	16408

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  34. #34
    Old Timer defaced's Avatar
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    Ok, watched your video. You've got the schematic and the board paired up correctly. Many of your questions circled around fundamental knowledge of the circuit and what the parts do. I'm going to try to give you a little bit of that that info here. Basically give you enough info so that if you want to read up on this stuff on your own, you have some words and concepts to start you off.

    Diodes: 1N4007 have a peak inverse voltage (PIV) rating of 1000v, 1N4006 have a PIV rating of 800v. Since diodes are intended to conduct in only one direction, PIV is the minimum voltage a diode can withstand when it is reverse biased (not conducting, or simply worded, when electricity is trying to flow backwards across the diode). The 1N4007 is the standard rectifier diode for amps; use that part.

    Preamp filter caps: The units for capacitance is always Farads. The "F" is often omitted for convenience. Without voltages noted on the schem (even the power transformer voltage is omitted), it'd difficult to say that the 500v caps would be sufficient just based on the documentation. However, experience says that 500v would be sufficient for the preamp nodes (C, D, E), but might be a little close one the screen node. Also note, 30u is an odd value (22u, 33u and 47u would all be more common). If you cannot find 30u caps, 33u would be the next best choice followed by 47u (assuming they will physically fit), then followed by 22u. Finding a real Mesa 2C+ schematic might be worth it so you can cross reference it to gleen any info that was omitted/incorrect on your schem.

    Plate filter caps: Caps in series add their voltage rating, so weather they're 300v or 350v caps, you're looking at either 600v or 700v effective rating for that filter node. Both will be excessive; 6L6s power tubes are rarely run above 500v.

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    -Mike

  35. #35
    Member WesPalladini's Avatar
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    Quote Originally Posted by defaced View Post
    Ok, watched your video. You've got the schematic and the board paired up correctly. Many of your questions circled around fundamental knowledge of the circuit and what the parts do. I'm going to try to give you a little bit of that that info here. Basically give you enough info so that if you want to read up on this stuff on your own, you have some words and concepts to start you off.

    Diodes: 1N4007 have a peak inverse voltage (PIV) rating of 1000v, 1N4006 have a PIV rating of 800v. Since diodes are intended to conduct in only one direction, PIV is the minimum voltage a diode can withstand when it is reverse biased (not conducting, or simply worded, when electricity is trying to flow backwards across the diode). The 1N4007 is the standard rectifier diode for amps; use that part.

    Preamp filter caps: The units for capacitance is always Farads. The "F" is often omitted for convenience. Without voltages noted on the schem (even the power transformer voltage is omitted), it'd difficult to say that the 500v caps would be sufficient just based on the documentation. However, experience says that 500v would be sufficient for the preamp nodes (C, D, E), but might be a little close one the screen node. Also note, 30u is an odd value (22u, 33u and 47u would all be more common). If you cannot find 30u caps, 33u would be the next best choice followed by 47u (assuming they will physically fit), then followed by 22u. Finding a real Mesa 2C+ schematic might be worth it so you can cross reference it to gleen any info that was omitted/incorrect on your schem.

    Plate filter caps: Caps in series add their voltage rating, so weather they're 300v or 350v caps, you're looking at either 600v or 700v effective rating for that filter node. Both will be excessive; 6L6s power tubes are rarely run above 500v.
    Thanks defaced nice post.

    I e mailed dimitry to take a look at your post and my video.

    As for the excessive voltages could it be because of the Sylvania STR-415 tubes the amp was designed for? I think they might have a higher voltage: TAD (tube amp doctor) 6L6GC-STR Tubes?? - Page 2 - Marshall Amp Forum

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