Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

Filament buss question

Discussion in 'Shock Brother's DIY Amps' started by moosie, Nov 23, 2017.

  1. milocj

    milocj Friend of Leo's Ad Free Member

    Aug 21, 2005
    Michigan
    I ultimately mounted my tank to the front panel, just like an original Fender Reverb Unit.

    As I mentioned, I didn't know it when I started, but Weber was still basically prototyping their kit and only had the chassis and board with the separate circuits on it. My OT is from a Champ and the choke is the same as a 6G15 which is the same as the BF amps. I sourced those and my parts through an amp tech buddy of mine (who has since passed on).

    He wasn't sure what to use for a PT so I contacted Ted Weber and he actually sent me a PT that was a prototype wind free of charge. The PT basically drove some of my build. It was too tall to mount inside the chassis which I think was the original intent (with the power supply caps in a doghouse like an original Fender). I had a custom cabinet made that was deeper to allow for the extra height of the PT.

    At the time I also couldn't find springs to suspend the tank from the four studs like Fender did so I contacted Ted again about the mounting (by this time he had a real kit) and he sent me that spring packet that you mentioned. I think their intent was to "float" the tank between springs and to cap them with the T-nut, except that I couldn't get any springs to work that way. I kept the tank on the floor of the cabinet loose for a while, and eventually found that Darren Riley had started selling the Fender springs from their '63 Reissue and was finally able to mount the tank like Fender did.

    It was a long journey and was surprised that there seemed to be so much of a ground noise issue on the net because mine is quiet. Hard to tell if I was good or lucky :lol: If you aren't familiar with the Fender mounting, there are four screws through the front panel. Their springs just thread onto those screws inside the cabinet and leave the end loop bent out at a little bit of an angle that extends just beyond the end of the screws. Another set of four springs hook to those loops and then go to the reverb pan.

    You end up with the pan suspended a little bit off the front panel of the cabinet and sort of in the middle of an X pattern between the four screws. Kind of difficult to describe but really quite simple in practice. No pics of that and I would have to pull the chassis of either my Revive or my original ''64 to take some. The Reissue documents on the Fender website might show the diagram and part numbers for mounting the tank.
     
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  2. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    Something like this...


    upload_2017-11-30_13-15-49.jpeg
     
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  3. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Thanks guys.

    I suspect the bolts on my cab would need to have more space between them, top to bottom, so the tank could float between. As it is, the bolts exactly fit the pan mounts. Plus, unless I were to either build a deeper cab, or move the tranny inside / caps into doghouse, there's just no room for the tank to float off the surface of the front panel, as the corner of the tranny only misses the tank by barely 1/8".

    There's not enough depth to mount the tank on the floor of the cab, either.

    All in all, a rather poor design, this Weber kit.

    I'm just going to bolt it to the front and hope for the best. Not a lot different from a Fender combo...


    20171130_151633.jpg
     
    Last edited: Nov 30, 2017

  4. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    I've been thinking about the options for grounding. Seems like the choices are:
    1. All grounds attach to single bus, near their respective circuits, and the bus attaches to chassis at input jack. Blencowe's basic scheme.
    2. Slight refinement to #1. Preamp only on the bus, and power grounds to the PT bolts. This is what @milocj did, if I got that right.

    And then there are a few elevation / isolation schemes:

    Follow the logic of either 1 & 2 above, except the bus attaches to the chassis NEAR the input jack. Jacks are insulated from chassis.

    Gehring does this in his build, but instead of running the grounds up to the area near the input jack, he goes the opposite direction, down by the power supply. And then, he connects to the chassis via the hum loop block circuit, but he distributes it. Resistor and diodes are near the power supply, and capacitor is near the input jack.


    Questions (and really I'm just trying to understand, not asking for a solution):

    If I split the grounds, with power section to PT bolts, and preamp on a bus, AND isolate the preamp via the hum loop block circuit, does the direct connection at the PT bolts eliminate any benefit of isolation? Must I ground *everything* to the bus if I want to isolate?

    Also, how important is it to run the single bus up to the area of the input jack, if I'm planning to isolate? Since it's connecting to the chassis through the hum loop block circuit, does it matter where?

    I could blindly follow Gehring's lead, but he only added the isolation after the fact, because it was noisy as hell. I wonder how he might have done it better, if he'd planned it from the start.
     
    Last edited: Nov 30, 2017
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  5. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    While I've been waiting for some parts, I've been using my drawing tool, working out how it will go together. Lots of stuff to cram in that tiny space.

    I'd love to ask you all to please have a look, but that's not fair. So just rejoice in a pretty picture, and wish me luck.

    The AC wiring on the left will actually be mostly crammed under the filter caps.

    I'm using insulated jacks, and elevating all DC grounds. I've separated the common returns into four groups, roughly aligning with the four power stages, labeled A, B, C, D. All the commons within a 'power group' connect together, and are then brought down to the main ground bus in the lower left corner. The idea is to keep flows local when possible.

    The little board in the lower left corner houses the elevation circuit. It will be bolted to the side of the chassis. One of those strongly nutted bolts will be THE ground connection. The other part of the circuit is one .047 uf cap running from the input jack common (insulated remember), to the Mixer pot shell (effectively the chassis).

    Hopefully, it'll be very quiet. :)


    Layout.png


    Here's a view of the under-board wiring. Picture the board oriented the same way, and you're looking through it. Solid lines are power rails. Dashed lines are commons. All color-coded by section.

    I know it's a bit anal, but I only want to do this once. And then if I succeed, I'll wanna do it once more. :D


    Layout2.png
     
    Last edited: Dec 5, 2017

  6. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Beautiful. Superb drawings, sir.
     
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  7. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    OK, time for a question. On the little mini-board in the lower left of my chassis (it will mount to the sidewall), is the elevation circuit. A 16R /5W resistor, in parallel with a pair of diodes.

    What spec on these diodes? I've never bought a diode before, that wasn't just for a pedal.

    Gehring doesn't say. It's not in the official plans, he added this during his initial build, and he calls it out, but no spec on the diodes.

    I'm missing a handful of things, and hoping to place an order this week.

    Thanks!

    Screen Shot 2017-12-05 at 4.57.15 AM.png
     

  8. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Moosie, don't proceed on my wild guess. :D If I'm wrong, I hope this'll get some expert to choke on his coffee and correct me.

    Not sure what the job qualifications are for those diodes. If they just have to be *robust*, you see 1N4007 used in both rectifier and bias circuits. Some specs are discussed here.

    Merlin says this talking about rectifiers:

    The diodes in a bridge rectifier need to have an average forward current rating that exceeds the maximum DC load current in your circuit. The popular 1N4007 is rated for 1 amp, which is far more than the maximum HT current in any guitar amp. However, something like a DC heater supply would probably need beefier diodes. Diodes also have peak and surge current ratings, but you don't have to worry about these as they are always well in excess of what you need, provided the average current rating is adequate for the job.
     
    Last edited: Dec 6, 2017

  9. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Thanks. Partly what's confusing me is that these diodes aren't on the rectifier / HT side. To paraphrase Gehring, they exist on the common return elevation hum-loop-block circuit to "prevent the potential between the isolated ground buss and the chassis from ever exceeding one diode forward voltage drop (0.7V)."

    The amp's fuse is 1 amp, but I'm not sure how much current could possibly run through these. I think in daily use it will be next to none - they seem to be more of a fault protection than anything else. In which case, do they need to be beefy? The isolation resistor in parallel with them, from DC common to chassis ground, is a 5 watter. You can make out one diode beneath the resistor. The other's there facing the other direction, just hidden in the photo. They look more pedal-sized than Twin recto sized. Not to be overly technical...



    rv4-55.jpg
     

  10. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    I remembered that the reissue '63 Reverb tank also has the hum-loop-block circuit. Looking at the schematic, and parts list, they're called "6A 400V 6A4". Mouser has these, which show a voltage drop of .95V (Gehring speaks of 0.7V, so these seem to be close enough).

    Here's the summary spec sheet:

    Screen Shot 2017-12-06 at 8.34.51 PM.png


    Here's the portion of the Fender schematic:

    Screen Shot 2017-12-06 at 8.26.48 PM.png

    Fender describes the operation of this circuit:

    "CR5 & 6 (across R23) provide an important safety feature. IF the guitar amp chassis becomes electrified, current will flow through the coax cable to the power supply ground of the Fender Reverb unit. The current will seek earth ground through R23. When R23 opens, the earth ground connection is broken. This will electrify the reverb unit’s ground and thus the guitar (ouch!). CR5 & 6 provide an alternate path to earth ground if R23 opens. "

    R23 is 15R, flame proof, just like I'm planning. It's rated at 1/4 watt, and on further research, I think I made up the 5 watt requirement. I guess I assumed, given the size of the one in Jeff's picture.


    So, I seem to have answered my own question. If someone thinks otherwise, please feel free.
     

  11. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Aha. They’re not there to prevent current flow but to allow it if it exceeds 0.7-0.95 V. Something like that.

    Your research is amazing.
     
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  12. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Yes. Not the amazing part. But thanks anyway :lol:

    Here's what I think I know up to this point:

    We typically overload the word 'ground'. DC commons typically attach to the chassis, as does the AC safety ground. Because of the AC, the whole chassis is guaranteed to be at zero volts potential, not counting some very minor resistances in the steel. The DC commons, including signal returns, are allowed to wander willy-nilly over the chassis, finding their best way 'home', back to the power company. This creates overlapping current flows, and when a higher current flow overlaps with a lower current (such as sensitive preamp) flow, noise results. Ground hum.

    What I'm trying to do is separate DC commons from the chassis. So, I'm calling them "DC commons", not ground, because they're not going to be quite at zero V, since they only are allowed to flow back to actual ground through one point, the resistor.

    In addition, I'm trying to arrange the DC commons into little packages, or loops, with their respective power sources, keeping the currents from overlapping. Because while we might be elevated, and running the DC commons over wires not a huge steel surface, it's still possible to have high current interfere with sensitive low-current areas.

    Blencowe talks about this in his grounding chapter. It's online, I'm sure we've all read it. I have the book, too, and that's handier, so here's a photo from that:

    20171207_170350.jpg

    The idea is that each filter stage gets it's own DC common return. They all join up in either a bus (decent) or multi-star (better) configuration, and only connect to actual ground at one point. A lot of us build that way. But not usually with insulated jacks and ground elevation. I'm doing this because this device, like the 6G15, is particularly sensitive to ground loops because of how it connects to the amp in two places: common ground from wall power, and the instrument cable.

    So, back to the elevation circuit: the DC potential will be a bit above 0 volts, but obviously for safety we don't want there to be much potential here. I'm not clear on the possible failure scenarios, but the diodes ensure that if the potential ever exceeds one forward voltage drop, they'll open, and equalize the voltage. For example, if the lead on the resistor were to break, and leave no return to chassis. You'd be back to having a noisy circuit, but not a deadly one.


    Anyway, that's how I'm thinking about it. It's taken me a few years of mulling this over to get here (hey, I'm slow). I'm not sure it's entirely correct, or if I'm glossing over other important elements. I am very much following Gehring's build, but at the same time, trying to incorporate what I've learned reading Blencowe. None of this DC common elevation is on the schematic and layout diagrams from the Weber kit. Well, half way. There is a reference to a single 16R resistor, but no diodes or filter cap, and no indication of what it's for, and no place for it on the eyelet board, and no insulated jacks, etc etc. Very much an afterthought in the kit. This, and my lack of understanding, is why it's taken me so long. Plus, I just let it sit on the shelf for a couple years, out of mild disgust over my ignorance.
     

  13. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Waiting on a few bits and pieces due early this week. I've got the board half done, and I think I've finished drilling new holes, or enlarging old holes, in the chassis. I moved the PT, the OT, and the AC strain relief. Had to enlarge 1/4" jack holes for insulating shoulder washers. Enlarged reverb jack holes so the metal bits don't touch the chassis. And that tube socket I had to replace... the new 9 pin looks like the others, but oddly fits a 7/8 hole, not 3/4 like the others, and VERY oddly, it's rotated 90 degrees, so when the mounting tabs line up with the chassis holes, the pins are all 90 deg off where they're supposed to be. I could have drilled new mounting holes, but decided to leave it, as they needed to be very close to the enlarged socket hole.

    step drill chassis.jpg

    20171210_024448.jpg

    I've also finished poking new holes and eyelets into the board. Note the nut & 4 different washers next to the 1/4" jacks. They go on like: lockwasher, black shoulder washer, fit through chassis hole, then flat brown insulating washer, trim washer, and nut.

    I dumped the horrible quality cream-gray chicken head knobs that came with the kit. I never liked chicken head knobs anyway. So now I got brownface knobs on a shellacked tweed cab.

    hardware.jpg

    components.jpg


    All power rails and returns (and nothing else) run under-board.

    power and return.jpg




    Moving right along... (this is the easy part)

    working on board.jpg

    board end.jpg


    That's it for a little while. Tomorrow is my every-tenth-day infusion. It takes all day (10 hours), and the aftermath usually knocks me down for a few days. By then my final mouser and Hoffman orders should have arrived. I'd like to get this finished for Christmas jamming, but I'm not sure how feasible that is. Working inside the cramped chassis will be slow.
     
    Last edited: Dec 10, 2017 at 2:49 AM
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  14. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City
    Wow, the 'easy part' would have me quaking in my boots. Just the empty board is terrifying. OTOH you *are* doing really nice work. Great pics, very helpful.

    Is it too late to re-title this thread something like "The world's most challenging 'easy' build?"
     
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  15. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    I asked the mods to please rename the thread so it reflected the content, but never heard back. I didn't want to start another, and split up the thread... So, all this is about that pesky heater wiring, supposedly. :rolleyes:

    I'm happy working on the empty board, because I made that very specific layout map ahead of time. The chassis is quite cramped, so that part is gonna be tough, I think.

    Thanks for the kind words. Hopefully this thing will work.
     
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  16. moosie

    moosie Doctor of Teleocity Silver Supporter

    Age:
    60
    Jul 18, 2010
    Western Connecticut
    Back again. I did take a little break after Sunday's infusion, but it wasn't too bad this time, so I took the opportunity to work on my son's Les Paul. It's got a new output jack, new bone nut, and new frets!


    Onward. Moving right along, and running out of components. The board is all populated, except for the power supply and a few shielded runs.

    I corrected an error on my layout. I had forgotten the under-board ground return wire, from the pair of caps just above V4. Glad I caught it now.

    Hoping to get the board wired in by the weekend.


    20171214_035149.jpg
     
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  17. King Fan

    King Fan Friend of Leo's Ad Free Member

    Jan 1, 2013
    Salt Lake City

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