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Thread: Brass grounding plate

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    Brass grounding plate

    Hi all can anyone tell me what the purpose of the brass grounding strip that the two stroke amp im building has? I can't work out what benefit it would have over a ground buss, is it to make soldering the ground leads easier? does it do a better job than a buss? and I suppose the main question is can I create a ground buss instead or would that create an earth loop?
    Thanks
    Scott

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    Quote Originally Posted by Jarvini View Post
    Hi all can anyone tell me what the purpose of the brass grounding strip that the two stroke amp im building has? I can't work out what benefit it would have over a ground buss, is it to make soldering the ground leads easier? does it do a better job than a buss? and I suppose the main question is can I create a ground buss instead or would that create an earth loop?
    Thanks
    Scott
    Scott Im still very new to this stuff too, so with that pound of salt : I'm just finishing building a Fender Deluxe style amp as well. The best I could determine: the pots on this amp are all mounted to this plate, from inside the chassis, as are the input jacks, so makes a very good ground contact for the pots and jacks. A few ground wires from the eyelet board that are on the preamp end of the circuit are also grounded here. Its very conductive, easy to solder to, and they also (back in the day) tucked the relatively low signal wire bundle leading to the vol, bass, treble, etc, controls down into the corner of this plate (Im guessing as well) for shielding. If you don't put the plate in, and use a buss, the grounds should be fine, but the FRONT (side mounted to chassis) of the pots, and input jacks won't have as good a conductor to mount to, since the Fender style steel chassis, with some oxidation that forms naturally, won't be as good a ground path. Also, look at the Marshall style chassis builds, they run a bus wire across the back of all the pots. Re grounding, all of the low signal stuff grounds to the brass plate, then all of (most of) the power filter stuff grounds in a different spot, on the chassis, over by the power transformer. At least for fender style builds. Cleaner/audio signals grounded in one area, dirty/power signals in another area. I don't think you need to worry about a loop unless you build one in: i.e. say you ground both ends of a shielded input jack wire. There are a whole LOT of great threads on this site regarding improving grounding schemes. (lots of great gurus here) check some of them out. Check out some of the great comments on grounding schemes on this thread: Yup, Another One... Kraken 50 Build: Round II (and look at the build quality, its a work of art)

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    Quote Originally Posted by Jarvini View Post
    Hi all can anyone tell me what the purpose of the brass grounding strip that the two stroke amp im building has? I can't work out what benefit it would have over a ground buss, is it to make soldering the ground leads easier? does it do a better job than a buss? and I suppose the main question is can I create a ground buss instead or would that create an earth loop?
    Thanks
    Scott
    The brass grounding plate is easy to solder to and it worked fine with vintage amps like Fenders. However, when using that, your grounding is just random to the chassis, which can cause problems with noise and hum and oscillations, depending on the circuit and gain levels you are using. A ground buss isn't really any better if it is also random chassis grounded, such as to the back of pots for example. Using a ground buss does allow you to control your grounding a bit better, but it has to be done correctly. With any grounding design, the safety ground should have it's own ground to the chassis within about an inch of where the power cord comes into the amp, and it should be made a little longer than the hot and neutral wires so that if the power cord is pulled out of the amp, the safety ground is the last thing that would be connected. It should use a bolt with two keps nuts and a terminal soldered to the wire. It should be a green wire with a yellow stripe, or a green wire, depending on your jurisdiction. You can look up what the code is for your country. In the US it is a green wire with a yellow stripe.

    Your buss bar should be ground for the signal grounds and should not connect to the same point as the safety ground. In order for the buss bar to be used correctly, it needs to be connected to the chassis at only one point, usually near the input, but it can also work if your connection point is near the power transformer....as long as there is only one chassis grounding point for the buss bar. This means that you need to use isolating jacks so that those will not ground on their own. Switchcraft makes longer shaft jacks that you can use isolating washers with. These are better quality jacks than Neutrick or Cliff plastic jacks. Do not ground to the back of the pots. They can ground fine with a star washer to the chassis. Any grounds off the terminals of the pots can go to the buss. All grounds should go to the buss in order....meaning that the cap that supplies your first preamp stage should have a local summing point where all grounds for that stage go. Then that summing point should go to the buss bar. Think of it as little streams leading into a river. The next stage would also have it's own local supply cap and a summing point, then ground to the buss in order after the first stage, etc. Do not ground anything to a transformer bolt either...that is a potential safety hazard. You should lay out the supply caps for each stage near the stages they supply rather than all in one spot like Fender did. If it is a kit that you building with a pre-determined layout that mounts all the caps in one place, then that isn't ideal but it will work. For more on the proper grounding with a buss bar, look up Kevin O' Conner's galactic ground (In his books) and/or Merlin's buss bar system in his books and on his website. I highly urge you to get Merlin's book if you don't have it already. It is VERY good. The Valve Wizard

    There is also the Hoffman system which uses a buss bar and rather than random chassis grounding, it uses controlled chassis grounding. It works ok too, but for high gain amps it may have issues. To me it is also more work than doing things the other ways I mentioned above, so I don't use it myself. You can find the Hoffman grounding system on his website. Tube amp parts, Guitar amp parts, Tube amp for guitar

    Greg
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    Thanks guys I think I shall buy a copy of the valve wizard I've got dave hunters the guitar amp handbook and the aspen pittman book but there's not much at all on grounding in either of those.
    I'm new to amp building myself but after 30 years of playing guitar I seem to have become obsessed with building my own valve amp and I am trying to learn as much as I can before I start the build!!
    I have been gradually selecting and purchasing the various components required (an expensive route i know) and trying to understand each stage of the amp rather than just chucking it together and hoping it works at the end!!
    i chose the two stroke amp (The revised version with only 1 6v6) from dave hunters book as it has some building instructions and it seemed like a fairly basic amp for me to start with
    So I also apologise for some of my questions which must seem like very obvious things to you experienced builders but we all had to start somewhere and I'm just trying to avoid any silly and perhaps costly mistakes
    Thanks
    Scott

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    20171017_202346.png
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    Quote Originally Posted by Jarvini View Post
    Thanks guys I think I shall buy a copy of the valve wizard I've got dave hunters the guitar amp handbook and the aspen pittman book but there's not much at all on grounding in either of those.
    I'm new to amp building myself but after 30 years of playing guitar I seem to have become obsessed with building my own valve amp and I am trying to learn as much as I can before I start the build!!
    I have been gradually selecting and purchasing the various components required (an expensive route i know) and trying to understand each stage of the amp rather than just chucking it together and hoping it works at the end!!
    i chose the two stroke amp (The revised version with only 1 6v6) from dave hunters book as it has some building instructions and it seemed like a fairly basic amp for me to start with
    So I also apologise for some of my questions which must seem like very obvious things to you experienced builders but we all had to start somewhere and I'm just trying to avoid any silly and perhaps costly mistakes
    Thanks
    Scott
    Good books. Also, check out some of the great posts by gurus like Aiken, this is a very good one: Grounding

    We sound like kindred spirits, same here, except Im not much of a guitarist but enjoy playing.

    I did almost the same thing, but tried really hard, and partially failed, to minimize the number of orders and hence shipping costs. Arrghh, forgot the 1 ohm resistors, blatt, forgot the 100 ohm resistors for the 6.3v heater line artificial ground, akkk, forgot the lamps for the pilot light, that sort of thing.

    Check out Rob Robinette's site, lots of great build info, and links.

    Good luck on your build, post lots of photos. Lots of real gurus here to learn from.

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    I've added a picture of the layout that I'm using so I can ask you all another question ?
    Should the wire from the 1.5k on the far right of the board go to the top lug of the input jack and have a wire connecting the middle lug to the top lug and should there be a wire connecting the top lug to the brass grounding plate as there is no mention of this in the build notes but the earth symbol leads me to believe the top lug should go to earth ?
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    Quote Originally Posted by soundmasterg View Post
    The brass grounding plate is easy to solder to and it worked fine with vintage amps like Fenders. However, when using that, your grounding is just random to the chassis, which can cause problems with noise and hum and oscillations, depending on the circuit and gain levels you are using. A ground buss isn't really any better if it is also random chassis grounded, such as to the back of pots for example. Using a ground buss does allow you to control your grounding a bit better, but it has to be done correctly. With any grounding design, the safety ground should have it's own ground to the chassis within about an inch of where the power cord comes into the amp, and it should be made a little longer than the hot and neutral wires so that if the power cord is pulled out of the amp, the safety ground is the last thing that would be connected. It should use a bolt with two keps nuts and a terminal soldered to the wire. It should be a green wire with a yellow stripe, or a green wire, depending on your jurisdiction. You can look up what the code is for your country. In the US it is a green wire with a yellow stripe.

    Your buss bar should be ground for the signal grounds and should not connect to the same point as the safety ground. In order for the buss bar to be used correctly, it needs to be connected to the chassis at only one point, usually near the input, but it can also work if your connection point is near the power transformer....as long as there is only one chassis grounding point for the buss bar. This means that you need to use isolating jacks so that those will not ground on their own. Switchcraft makes longer shaft jacks that you can use isolating washers with. These are better quality jacks than Neutrick or Cliff plastic jacks. Do not ground to the back of the pots. They can ground fine with a star washer to the chassis. Any grounds off the terminals of the pots can go to the buss. All grounds should go to the buss in order....meaning that the cap that supplies your first preamp stage should have a local summing point where all grounds for that stage go. Then that summing point should go to the buss bar. Think of it as little streams leading into a river. The next stage would also have it's own local supply cap and a summing point, then ground to the buss in order after the first stage, etc. Do not ground anything to a transformer bolt either...that is a potential safety hazard. You should lay out the supply caps for each stage near the stages they supply rather than all in one spot like Fender did. If it is a kit that you building with a pre-determined layout that mounts all the caps in one place, then that isn't ideal but it will work. For more on the proper grounding with a buss bar, look up Kevin O' Conner's galactic ground (In his books) and/or Merlin's buss bar system in his books and on his website. I highly urge you to get Merlin's book if you don't have it already. It is VERY good. The Valve Wizard

    There is also the Hoffman system which uses a buss bar and rather than random chassis grounding, it uses controlled chassis grounding. It works ok too, but for high gain amps it may have issues. To me it is also more work than doing things the other ways I mentioned above, so I don't use it myself. You can find the Hoffman grounding system on his website. Tube amp parts, Guitar amp parts, Tube amp for guitar

    Greg
    Hi Greg, I found photos of a few Marshall style builds, where they put a big ground buss wire across the back of all the pots, but also put little rubber or plastic rings to isolate the pots where they mount to the chassis. If hte bus wire is then run to one point on the chassis, would that fix the random ground point issue?

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    Quote Originally Posted by Jarvini View Post
    I've added a picture of the layout that I'm using so I can ask you all another question ?
    Should the wire from the 1.5k on the far right of the board go to the top lug of the input jack and have a wire connecting the middle lug to the top lug and should there be a wire connecting the top lug to the brass grounding plate as there is no mention of this in the build notes but the earth symbol leads me to believe the top lug should go to earth ?
    Check with the gurus, but I believe the middle and top lug on your input jack (in your diagram) get wired together and then to ground. If you look at a shorting switchcraft jack, it will make sense to you. If you use an isolated input jack grounding scheme like Greg wrote about above, you'll need a ground wire. For Fender style, that is bolted to the brass plate, it will get grounded there.

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    Does that mean that if I use the brass plate method I don't need to run a wire from the top lug of the input jack and solder it to the brass plate ?

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    Ahh, this is what I was looking for:
    https://www.tubesandmore.com/sites/d...2a_drawing.gif

    The "tip" is your input signal, clockwise tab as viewed from the bottom.
    The shunt is the middle tab. You wire the jack so that when there is no guitar plugged into the jack, the shunt connects the tip connection to ground, which is the counter clockwise tab (top tab in your schematic). This is so you don't get garbage signal going into your amp when nothing is plugged in.
    The ring is the outer tab that goes to the shield on your guitar cord. it will get grounded somehow, depending on your grounding scheme, either to the brass plate, or for the isolated jack scheme, a wire to ground.

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    Quote Originally Posted by Jarvini View Post
    Does that mean that if I use the brass plate method I don't need to run a wire from the top lug of the input jack and solder it to the brass plate ?
    Yes, you won't need a wire if you bolt the jacks and pots to the brass plate. See
    http://www.tjadamowicz.com/amps/gall.../BFamps048.jpg
    for the isolated w ground bar case. There, he has the little red isolators behind the input jack, then wires the counter clockwise most lug (the "ring") to his ground bus.
    in the standard old style fenders, the jack is screwed tightly to the brass plate, so the ring is grounded that way, so no wire needed on the counter clockwise most lug.

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    Thanks I see now, the top lug is already grounded as it's in contact with the brass plate already and adding a wire from the top lug to the brass plate would create an earth loop is that right?
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    Just like to say thanks for your help Mike helped me a lot and as for the photos you posted some super neat workmanship out there
    Scott
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    Ooh, another tip I got from the gurus: the 68k resistor leading from your input jack to V1 is a grid stop. Its there to help prevent radio signals and other garbage from getting into your amp, and also to help prevent parasitic oscillations. They didn't have shielded wire in the old days, so they put the resistors right on the input jacks. I was told by several gurus to move the grid stop resistors to the pin on the preamp tube, and also ground the shield on the shielded cabe to the other side, the side nearest the jacks. The former will let the grid stop work better, and the latter will be in keeping with the grounding scheme.

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    Thanks again Mike can't thank you enough.
    I take it that means the shield gets grounded to the top lug of the input jack rather than an earth tag on the 9 pin tube socket bolt
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    Also, Scott, if you haven't yet done so, please check out the many great tutorials on draining the filter caps. It's a matter of life or death (or severe injury!!) Can't wait to see photos of your build, and hear some sound clips!

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    You may like to take a look at this for grounding a Fender AB763. http://sluckeyamps.com/misc/AB763_Deluxe_Lite.pdf
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    Mac, nice work, thanks for the link.

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    Thanks for the heads up on the filter caps Mike don't worry I've watched numerous you tube tutorials on how to safely discharge the caps and safe working practices with tube amps I did stumble across a guy called roy Blankenship whilst trawling the net and his amps looked fantastic! I'll post some pics of the build in due course I'm building the amp as a head instead of a combo as I have a few different speakers I'm going to build into cabs as well for different impedance options so it might take a while but Rome wasn't built in a day and all that
    Thanks again
    Scott

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    Quote Originally Posted by Jarvini View Post
    I've added a picture of the layout that I'm using so I can ask you all another question ?
    Should the wire from the 1.5k on the far right of the board go to the top lug of the input jack and have a wire connecting the middle lug to the top lug and should there be a wire connecting the top lug to the brass grounding plate as there is no mention of this in the build notes but the earth symbol leads me to believe the top lug should go to earth ?
    The 1.5k resistor in your linked layout is a cathode resistor. The two caps next to it are connected to a switch in order to switch to different gain levels. All of these go from pin 3 of the tube (the cathode) to ground. If you use a random chassis ground method like Fender's with their brass plate then grounding it at the same place as the rest of the preamp stages is fine, or you can ground it through the jack contact like they show in the layout. If using a bus bar method with isolated jacks, then you need a wire to go from the top lug of the jack on your layout diagram to the ground buss. It all depends on what ground scheme you use.

    As Mike mentioned, the 68k works best as a grid stop if it is connected directly to the tube socket with a short lead. That resistor also serves to isolate the inputs from each other if you have dual inputs like on a vintage Fender. It will function fine on the board also as the many vintage amps working fine all these years can attest to. It just works better if mounted directly to the socket. The 'grid stop' function of that resistor becomes more critical in later stages, but keep in mind that most vintage amps didn't use grid stops except for the 68k on the input, and they mounted them everywhere except right at the socket, so it isn't something that is completely necessary in all designs on every stage in the amp. There should always be one on the input however or your amp can oscillate or start to amplify radio.

    @Mike, the pots usually ground to the chassis with their star washers and nuts. All that is grounding at that point is the pot casing btw. If you are going to go to the trouble of soldering a buss to the back of the pots then isolating them helps, but it isn't really necessary to go to all that trouble. The pot casings ground fine to the chassis as long as the nuts are tight and you use the star washer, but grounding the pot casing is just helping with shielding. The circuit grounds are what really matter and any point on the pot lugs that is grounding should be controlled rather than random. Most of the pots casings today are not easy to solder to and for something that isn't really necessary, it is a lot of trouble to go to in order to make it functional. Remember that any buss to the back of the pots is so the casing will help in shielding, but it has nothing to do with your circuit grounds.

    Greg
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    Quote Originally Posted by soundmasterg View Post
    ...

    @Mike, the pots usually ground to the chassis with their star washers and nuts. All that is grounding at that point is the pot casing btw. If you are going to go to the trouble of soldering a buss to the back of the pots then isolating them helps, but it isn't really necessary to go to all that trouble. The pot casings ground fine to the chassis as long as the nuts are tight and you use the star washer, but grounding the pot casing is just helping with shielding. The circuit grounds are what really matter and any point on the pot lugs that is grounding should be controlled rather than random. Most of the pots casings today are not easy to solder to and for something that isn't really necessary, it is a lot of trouble to go to in order to make it functional. Remember that any buss to the back of the pots is so the casing will help in shielding, but it has nothing to do with your circuit grounds.

    Greg
    (Scott, don't mean to hijack your thread, this is a great topic hope you don't mind a few related questions . . .)

    Greg, thanks! I am still not very nimble with the big soldering iron, and was afraid to melt a bunch of stuff, so in my recent build, I didn't solder anything to the back of any pots (ground, etc). Anyplace that needed a ground, I routed a wire. Sounds like Im not quite there yet since I routed ground wires onto the brass plate (of a AB763 Deluxe type frankenstein) but the grounds are not not all in the same spot, and there are quite a few. (6 total)


    Re http://www.thevintagesound.com/ffg/s...763_layout.gif there are 2 grounds one on the vol and one on the bass pots, and then the shielded wiring will produce a 3rd, for each channel. If these ground wires are all run down to the brass plate, but not at a star, will this cause a problem? Its not a bus type, but not fender type either. I could never figure out why they'd solder something to the back of a pot that was a ground in the schematic. If the pot got loose, then all kinds of crackle and hum could occur (had that happen on a really ancient blackface princeton I had ages ago). Maybe its a "Danger Will Robinson" to tell you to go tighten the pots?

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    hijack all you want the more i can learn the better and as ive had some great help so far i might as well post this here too

    this is what ive currently sourced for my build
    all my signal caps are tube amp doctor mustard caps
    the filter caps are sprague atom as are the 25uf/50 electrolitics
    500pf silver mica cap for the tone to volume pot
    switchcraft jacks
    allen bradley 1 meg audio pots
    classic tone usa 40-18031 15w output transformer
    ceramic valve sockets
    mini boost switch
    1.5mm grp sheet which i will make my own turret board from (i have the turrets too) i know fenders use eyelet board but i think turret boards look neater and will be a bit easier to work with
    im going to opt for carbon comp resistors (allen bradley) im going to purchase these in one hit if i can as the postage from the usa will kill me if bought seperately

    ive also bought lots of different wire various gauges and colours but its all stranded not sure if solid core would be easier to work with though?

    so whats left well im going to build it in a much larger chassis than a champ probably a jtm 45 size which i will buy blank and have my engineer friend do all the hole cutting for me (handy friend to have) im going to make it so the valves come out the top not the back

    now for the questions
    1) the output transformer has three output options 4/8/16 ohm can i build the amp using all three options with three output jacks instead of two (only ever using one) as i have 4/8/16 ohm speakers that im going to build in cabs

    2)what would the best power transformer be as the suggestions in the book seem to be hard to locate the specs are as follows:-

    240v primary
    secondary 310v-0-310v to 330v-0-330v (rated for at least 70mA-80mA)
    center tapped 6.3v ac filament supply at 4A
    5.0v ac rectifier filament supply at 3A

    what do you think so far ? i know you guys could probably build this amp with your feet in the dark but as its my first i welcome any advise
    Dave Hunter was right though it is a minefield of contradicting opinions and preferences and very very addictive and i love it even if it is costing me small fortune in postage from the states
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    Quote Originally Posted by mikepukmel View Post
    (Scott, don't mean to hijack your thread, this is a great topic hope you don't mind a few related questions . . .)

    Greg, thanks! I am still not very nimble with the big soldering iron, and was afraid to melt a bunch of stuff, so in my recent build, I didn't solder anything to the back of any pots (ground, etc). Anyplace that needed a ground, I routed a wire. Sounds like Im not quite there yet since I routed ground wires onto the brass plate (of a AB763 Deluxe type frankenstein) but the grounds are not not all in the same spot, and there are quite a few. (6 total)


    Re http://www.thevintagesound.com/ffg/s...763_layout.gif there are 2 grounds one on the vol and one on the bass pots, and then the shielded wiring will produce a 3rd, for each channel. If these ground wires are all run down to the brass plate, but not at a star, will this cause a problem? Its not a bus type, but not fender type either. I could never figure out why they'd solder something to the back of a pot that was a ground in the schematic. If the pot got loose, then all kinds of crackle and hum could occur (had that happen on a really ancient blackface princeton I had ages ago). Maybe its a "Danger Will Robinson" to tell you to go tighten the pots?
    I've never bothered to solder to the back of pots. I've done it in guitars but in the amps there is no point as if mounted correctly with the serrated washer and the nut, it will ground the case of the pot to the chassis. Grounding to a brass plate at multiple points is the same as a random chassis ground, since the brass plate is contacting the chassis at many points. It isn't even necessary to ground the signal ground to the chassis in order for the circuit to function. The chassis is a convenient reference point that can help with shielding but the amp will function without being grounded to the chassis. You still always need the safety ground to the chassis....that is required by code. Sometimes a piece of equipment will have a ground lift switch, especially studio recording equipment that is meant to connect to multiple chassis. When ground is lifted, then you have a particular sized resistor and capacitor that ground goes through on its way to the chassis which grounds it at AC.

    Grounding randomly to the chassis will work....most vintage amps were done this way. There are better ways though, which you are discovering. Instead of using a brass grounding plate, connect all of your grounds to a buss bar that is on your board. The connect that buss at one end only to the chassis....say at the input of the amp. Use isolated jacks and connect all their ground points to the buss also, along with any other grounds in the amp...BUT, connect them in the proper places on the buss bar. In order for this to work properly, do not locate all your filter caps in one spot like Fender does...put them near the circuits they supply so you can have local stars where each circuit supplied by the cap will connect.

    I'll have to look at your link and comment later...gotta leave work for the day.

    Adding to prior comments:

    The link you attached is just a vintage Fender, which used random chassis grounding. It works ok for lower gain circuits like that particular Fender but hums more than it should and as you get more gain, it doesn't work very well at all. Adding a shielded cable doesn't really have any detriments as long as you only ground one end of the shield. If your grounding scheme is the random chassis ground, then adding your shield to the back of a pot or to the brass isn't going to make a difference. Its no ground loop because only one end of the shield is grounded.

    Fender made their amps with the grounds to the back of the pots because they could wire up the pot outside of the amp and just put the pot in and not have to solder another wire. It took less time and money basically. Also, back in the day, most of the general population was somewhat familiar with tubes and tube circuits since they were still in use in general consumer products, so they were aware of the pitfalls, and if a pot came loose they might have had an idea that they may have to tighten up a pot.

    Greg
    Last edited by soundmasterg; 10-19-2017 at 02:10 AM. Reason: Adding to previous comments
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    Quote Originally Posted by Jarvini View Post
    hijack all you want the more i can learn the better and as ive had some great help so far i might as well post this here too

    this is what ive currently sourced for my build
    all my signal caps are tube amp doctor mustard caps
    the filter caps are sprague atom as are the 25uf/50 electrolitics
    500pf silver mica cap for the tone to volume pot
    switchcraft jacks
    allen bradley 1 meg audio pots
    classic tone usa 40-18031 15w output transformer
    ceramic valve sockets
    mini boost switch
    1.5mm grp sheet which i will make my own turret board from (i have the turrets too) i know fenders use eyelet board but i think turret boards look neater and will be a bit easier to work with
    im going to opt for carbon comp resistors (allen bradley) im going to purchase these in one hit if i can as the postage from the usa will kill me if bought seperately

    ive also bought lots of different wire various gauges and colours but its all stranded not sure if solid core would be easier to work with though?

    so whats left well im going to build it in a much larger chassis than a champ probably a jtm 45 size which i will buy blank and have my engineer friend do all the hole cutting for me (handy friend to have) im going to make it so the valves come out the top not the back

    now for the questions
    1) the output transformer has three output options 4/8/16 ohm can i build the amp using all three options with three output jacks instead of two (only ever using one) as i have 4/8/16 ohm speakers that im going to build in cabs

    2)what would the best power transformer be as the suggestions in the book seem to be hard to locate the specs are as follows:-

    240v primary
    secondary 310v-0-310v to 330v-0-330v (rated for at least 70mA-80mA)
    center tapped 6.3v ac filament supply at 4A
    5.0v ac rectifier filament supply at 3A

    what do you think so far ? i know you guys could probably build this amp with your feet in the dark but as its my first i welcome any advise
    Dave Hunter was right though it is a minefield of contradicting opinions and preferences and very very addictive and i love it even if it is costing me small fortune in postage from the states
    Im too much a newby to tell you what to buy, but your parts look pretty similar to what I got, with a few exceptions.
    The spragues are really expensive, ended up with F&T brand. Specs looked good and quality reviews are good as well.
    Classic tones have a good rep. Only reason I got hammonds is that they fit the chassis I got on Ebay.

    Ask around the gurus here about carbon comp resistors. I think you're better off with metal film most anywhere in your circuit.
    I got stranded wire due to suggestions on this blog. A few of the more experienced builders says that if you bend back and forth, which we'll probably do as new builders, the solid will break more easily, and really tough to find when a break is inside the insulation.
    Awesome idea to put your build in a big chassis in a head box. I fought too hard to wire up this thin fender style with my still weak soldering and general building skils. Wish I had used a head style box and bigger chassis.

    Re the transformer specs, 3a seems fairly standard for 5v sec. since a 5AR4/GZ34 use 1.9A on the 5v line.
    Seems like you have a lot more current on your 6.3v line than necessary. A 6V6 takes 0.45a, so two take 0.9a, 6 12AX? take 0.3a each or 1.8a, so a deluxe reverb with tremolo needs about 2.7a filament, so 4a is quite a bit higher than you need (as far as I can tell).

    Hammond Mfg. - REPLACEMENT & UPGRADES - Tube Guitar Amplifier - Power Transformers

    The single ended OT's have about 2a on the 6.3 sec, the two 6V6 (e.g. deluxe) have 3a on the 6.3 and bigger, e.g. vibrolux 2x 6L6 have 4a.
    So, you would probably be able to get away with a smaller power transformer, unless you're planning on adding lots of stuff later.

    Oh man, I wish I could build one of these that easily. Ive been months on my first build, still not done. But .... I haven' blown anything up yet!
    Jarvini likes this.

  26. #26
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    Thanks Greg.

  27. #27
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    Quote Originally Posted by Jarvini View Post
    this is what ive currently sourced for my build
    all my signal caps are tube amp doctor mustard caps
    the filter caps are sprague atom as are the 25uf/50 electrolitics
    500pf silver mica cap for the tone to volume pot
    switchcraft jacks
    allen bradley 1 meg audio pots
    classic tone usa 40-18031 15w output transformer
    ceramic valve sockets
    mini boost switch
    1.5mm grp sheet which i will make my own turret board from (i have the turrets too) i know fenders use eyelet board but i think turret boards look neater and will be a bit easier to work with
    im going to opt for carbon comp resistors (allen bradley) im going to purchase these in one hit if i can as the postage from the usa will kill me if bought seperately

    ive also bought lots of different wire various gauges and colours but its all stranded not sure if solid core would be easier to work with though?

    so whats left well im going to build it in a much larger chassis than a champ probably a jtm 45 size which i will buy blank and have my engineer friend do all the hole cutting for me (handy friend to have) im going to make it so the valves come out the top not the back

    now for the questions
    1) the output transformer has three output options 4/8/16 ohm can i build the amp using all three options with three output jacks instead of two (only ever using one) as i have 4/8/16 ohm speakers that im going to build in cabs

    2)what would the best power transformer be as the suggestions in the book seem to be hard to locate the specs are as follows:-

    240v primary
    secondary 310v-0-310v to 330v-0-330v (rated for at least 70mA-80mA)
    center tapped 6.3v ac filament supply at 4A
    5.0v ac rectifier filament supply at 3A

    what do you think so far ? i know you guys could probably build this amp with your feet in the dark but as its my first i welcome any advise
    Dave Hunter was right though it is a minefield of contradicting opinions and preferences and very very addictive and i love it even if it is costing me small fortune in postage from the states
    The TAD mustard caps will work fine, but so would Mallory 150's, Sozo's, Jupiters, polyester Orange Drops like the 6PS series, etc. As long as the caps aren't leaking DC and are polyester then the amp will sound fine...if you use polypropylene caps, then sometimes they can be a little too good for a guitar amp and the highs will be a little harsh. For hifi polypropylene is great though. But cap differences are very subtle so it isn't a huge difference from brand to brand or type to type with like values.

    Sprague Atom electrolytic caps are VERY overpriced and shouldn't be used anymore these days. They are old technology and are often a modern cap inside the very large Sprague case. At three times the price that is stupid. They will work ok though.....but in the future, get some F & T, Xicon, Rubycon, Nichicon, or Panasonic's. Stay away from Illinois caps...they are not very good.

    The silver mica makes things a little smoother in that position...sometimes the ceramic sounds better there also. Those caps are cheap so you can try either one.

    Switchcraft jacks are great, though if you got the standard ones, you can't fit the isolating washers on them. They sell longer shaft ones for that purpose....so with those ones you have, you'll have to use the random chassis grounding or any other method that does not use isolated jacks.

    Allen Bradley pots are fine but no need to go 1M....the usual 1/2 watt are fine.

    Those transformers are fine.

    The ceramic sockets will be ok as long as they were good quality. Ceramic sockets are harder to tension, and they won't arc like the plastic types will, but the tension part is what I don't like. McMurdo, Cinch, Belton all made good sockets and I know Belton is still around...not sure about the other two. The McMurdo and Cinch were UK based companies I believe so you might find more of them over there in surplus places.

    Allen Bradley made good carbon comp resistors, but those type of resistors are noisy and their values change with applied voltage, heat, age, etc. They cause distortion that can be pleasing to the ear but only if used in positions where there is lots of voltage swing, such as the plate resistors in a phase inverter. Otherwise, good quality metal film will make for a much quieter hum and hiss level in your amp and they sound fine. Just make sure to get good quality metal film and not cheap crap from China. One other caveat with metal film resistors and a lot of modern resistors is that they don't have long leads when compared to vintage stuff so you have to redesign the layouts in the amp to fit the modern parts. Carbon comp resistors are also more expensive these days than metal film in most cases. Carbon Film is a middle of the road choice but they are cheap and sound fine also.

    Stranded wire is a better choice. Solid core is easier to put in place where you want it, but the wire is often nicked when you strip it and then eventually it will fail. Teflon wire will stay in place with stranded but it is hard to strip. Not all wire is created equally either btw. The wire that Weber sells comes from China I think and it is pretty lousy....but Hoffman sells good stuff...AES/CE Dist sells good stuff. I get mine locally at a supplier for Intel for a great price for PVC and Teflon. For the vintage style cloth covered I get it from Hoffman. There is also Apex JR for some great surplus stuff. Word of advice...pick a color code to use for your wiring so it is easier to spot what is what when you look in the chassis. For instance, red is B+ and plates, orange is screens, green is heaters, brown is cathodes, purple are grids, etc.

    Just put three jacks on the back and label them accordingly and use whichever one you want at a time. Example: plug your 8 ohm cabinet into the 8 ohm jack. Next week plug your friend's 4 ohm cabinet into the 4 ohm jack, and the next time plug your 16 ohm cabinet into the 16 ohm jack. Just be sure to match your load up and you are fine as long as your speaker cab can handle the power.

    I'm not sure as far as the power transformer. Look around a bit. Classic Tone, Heyboer, Weber, Hammond....all of them are fine and reasonably priced. Mercury Magnetics are fine but they are WAY overpriced. I like Hammonds for power transformers but don't like them much for outputs. In the UK there are likely many surplus around but maybe you can purchase Drakes or Radiospares or something like that. I use Heyboer a lot for my home brewed stuff, but I often have them make me custom stuff.

    Greg
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  28. #28
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    Quote Originally Posted by soundmasterg View Post
    re ... Teflon wire will stay in place with stranded but it is hard to strip. ...
    Greg
    More newbie stories:

    Oh yeah, found out the hard way! I bought this high rolling no-nick wire stripper. Tried it out on a bunch of stuff around the house, worked great. Then I bought a bunch of mil spec stranded, silver coated copper, teflon insulation for the amp build. Aaaand, the no nick stripper won't strip the dang stuff. it peels the insulation off one side, but won't strip it. So, it was back to the awful ordinary strippers, but still really hard to strip. I finally figured out to first setup the stripper for a little bit bigger gauge wire than Im using, so the blade doesn't touch the wire, then grab the wire with the stripper, then rotate the stripper around the wire a few times to score that tough teflon, and pull hard. About 50% of the time only one side of the wire tears, but the wire doesn't get nicked, so I can peel the teflon off the wire, and cut it with a clipper. Really wish the high rolling strippers worked.

    A benefit of this wire is that it takes a HUGE amount of heat. The insulation on the transformers starts to melt back a bit if I hold the soldering iron on just a second too long, but Ive unsoldered, moved and re-soldered the mil spec wire and the insulation is still perfect. Even bumped the iron tip into the insulation a few times and it just leaves a little waste solder mark on it, it doesn't burn it. Amazing stuff that way. I think I'll still use it on the next build and try to find a better stripper made for this stuff.

  29. #29
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    Thanks for all your help guys so glad I found this forum and that people are so willing to offer such solid advice really helpful things are starting to make sense now
    Scott
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  30. #30
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    Quote Originally Posted by mikepukmel View Post
    More newbie stories:

    Oh yeah, found out the hard way! I bought this high rolling no-nick wire stripper. Tried it out on a bunch of stuff around the house, worked great. Then I bought a bunch of mil spec stranded, silver coated copper, teflon insulation for the amp build. Aaaand, the no nick stripper won't strip the dang stuff. it peels the insulation off one side, but won't strip it. So, it was back to the awful ordinary strippers, but still really hard to strip. I finally figured out to first setup the stripper for a little bit bigger gauge wire than Im using, so the blade doesn't touch the wire, then grab the wire with the stripper, then rotate the stripper around the wire a few times to score that tough teflon, and pull hard. About 50% of the time only one side of the wire tears, but the wire doesn't get nicked, so I can peel the teflon off the wire, and cut it with a clipper. Really wish the high rolling strippers worked.

    A benefit of this wire is that it takes a HUGE amount of heat. The insulation on the transformers starts to melt back a bit if I hold the soldering iron on just a second too long, but Ive unsoldered, moved and re-soldered the mil spec wire and the insulation is still perfect. Even bumped the iron tip into the insulation a few times and it just leaves a little waste solder mark on it, it doesn't burn it. Amazing stuff that way. I think I'll still use it on the next build and try to find a better stripper made for this stuff.
    You could try a thermal stripper for the teflon. I've got one and it works well, but I usually just use the regular PVC stranded with a normal stripper. Once you get good with your soldering skills you will rarely melt the insulation. Make sure to use a temp controlled soldering station rather than just a soldering iron that just plugs in. They work MUCH better and allow your soldering to improve 100%. Also pre-tin your tip with leaded solder before you touch it to your joint. It will transfer heat better and quicker to the joint so you spend less time with the iron heating the joint and other things up. Make sure your tip is clean too...every time you go to solder, clean it then pre-tin. Another benefit to the soldering stations is that the tips last MUCH longer.

    Greg
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  31. #31
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    Quote Originally Posted by Jarvini View Post
    Thanks for all your help guys so glad I found this forum and that people are so willing to offer such solid advice really helpful things are starting to make sense now
    Scott
    You're welcome! Keep practicing and reading and learning and you'll get better.

    Greg
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  32. #32
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    The only bit I don't understand is this:-
    If I isolate all the jacks and pots ( I take it switches too) from the chassis then the pots shells will not be earthed do I have to run a wire from the pots shell to the ground bus as well also the output jacks will not be earthed so these will also have to be attached to the ground bus which will mean running the ground bus round to the back of the amp as well like a large horseshoe or can these be grounded elsewhere and as I am using 4/8/16 outputs should the ground be from the first output jack (4 ) or from the last (16)
    I know the ac input has it's own ground and that the centre taps from the pt have there own near the pt but do all the others connect to the bus in succession as if it were the brass plate I.e input first large filter cap last
    ��

  33. #33
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    Quote Originally Posted by Jarvini View Post
    The only bit I don't understand is this:-
    If I isolate all the jacks and pots ( I take it switches too) from the chassis then the pots shells will not be earthed
    The input and output jacks can be isolated but the pots and switch shells should be earthed (bolted to chassis). It's as soundmasterg said in post #24

    "I've never bothered to solder to the back of pots. I've done it in guitars but in the amps there is no point as if mounted correctly with the serrated washer and the nut, it will ground the case of the pot to the chassis."
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  34. #34
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    Quote Originally Posted by Jarvini View Post
    The only bit I don't understand is this:-
    If I isolate all the jacks and pots ( I take it switches too) from the chassis then the pots shells will not be earthed do I have to run a wire from the pots shell to the ground bus as well also the output jacks will not be earthed so these will also have to be attached to the ground bus which will mean running the ground bus round to the back of the amp as well like a large horseshoe or can these be grounded elsewhere and as I am using 4/8/16 outputs should the ground be from the first output jack (4 ) or from the last (16)
    I know the ac input has it's own ground and that the centre taps from the pt have there own near the pt but do all the others connect to the bus in succession as if it were the brass plate I.e input first large filter cap last
    ��
    The jacks should be isolated from the chassis with a ground buss as the signal coming into the amp is bouncing around ground, up above it and down below it, just like a sine wave on a scope. If you want to avoid noise and hum, then isolating the jacks helps you towards that goal when using a ground buss that only contacts the chassis at one point. The pots and jacks can ground with bolting them to the chassis with serrated washers without issue as there is no signal on the cases of the pots and switches. Make sure there is a good mechanical connection and that is all you need. Some of the pot terminals are grounded depending on their location in the circuit, but that is a different thing entirely than the case of the pot. Just ground those at the appropriate point along the buss.

    Regarding the buss grounding to the chassis, many say to ground at the input because you can then shunt any noise on the input to ground right away before it enters the circuitry in the amp, however I have instead grounded the buss at the main cap ground successfully without any issues and a very quiet amp in terms of hum and noise level. Each preamp stage and the phase inverter stage had their filter caps mounted right near the stage with a local ground node for that stage, and then each of those nodes grounded to the buss in order. I used isolated input and output jacks, and the ground for the input grounded at the beginning of the buss and the output jacks grounded where the buss contacted the main cap, and that is also the only place where the buss grounded to the chassis. The amp also had a safety AC ground point that was a different place from that buss ground. I grounded at the main cap in this amp for two reasons. The first is that an audio engineer friend of mine who has been an engineer for 50 years told me it is fine to ground there, and the second is that a Conn organ amp that I have modified grounded there with a buss and it was very quiet. I believe in Merlin's system he does the same thing essentially as far as local cap nodes, grounding to the buss in order, isolated jacks, etc., but grounds at the input instead. He also grounds the main cap to the buss rather than having a separate ground. I'd have to read his book again or look at his site again to be sure but I believe that is the case.

    As you can see there are many ways to do the same thing, which is to minimize ground loops and hum and noise, and several of them work well. The key is to use a ground 'system' and to stick to it fully in your build. I've experimented with different methods of construction in the amps I've made and with each one I refine what I am doing and how I do it. The first amp I modified was a Silvertone 1484, which is a horrible layout from the factory. I isolated the grounds on that one in order to get some control over where I was grounding, but I didn't use isolated jacks. I also upped the gain and modified channels, added Fender reverb, etc., and with that amp I discovered there is only so much you can do to correct poor layout choices like putting the power transformer in the middle of the chassis right behind the inputs to channel 2 like they did! That amp becomes very quiet if I carefully stick some Mu-metal between the input to channel 2 and the power transformer, but Mu-metal is very expensive. Later I modified a rebuilt a Sunn 200S and used complete ground buss, jack isolation, and a circuit ground lift switch as Kevin O'Connor recommends. That one works well and is very quiet and can be used in combination with other amps at the same time with an overall lower hum level due to the addition of the ground lift switch. That one was a LOT of work to accomplish as modifying an amp to have a true isolated ground is harder if the amp was already made with random chassis grounding than if you build it from scratch with proper grounding from the beginning. Later I made myself a true PTP amp using a gutted Bogen chassis and transformers with my own circuit and layout. True PTP requires careful layout before the fact so you can plan everything including the grounds. That amp suffers from the Bogen transformer placement (right next to each other with nothing turned so there is a little more hum than I would like) but overall it works well and many people have asked me to build them one.... maybe someday I will but I'm still experimenting for now. I also built a Vox AC100 clone with an added higher gain channel, using turrets and a board and a isolated buss that grounds at the main filter cap and isolated jacks. This amp's hum level and noise is VERY low. I've also modified some vintage amps optimizing things but have kept the random chassis grounding and many of these are quiet too. So I guess in summary, it helps to build, no matter what design you are using, and you can get the hands-on learning started sooner.

    Greg
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  35. #35
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    Thanks guys it's a bit of minefield the subject of grounding I'll draw out a schematic showing what I have planned using all the information I have digested and post it here to make it easier to see and if you good fellows fancy it tell me what your opinions are?

    Thanks
    Scott
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