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Critique My 5F2A Build

Discussion in 'Amp Tech Center' started by Sylas Wojo, Oct 14, 2020.

  1. Sylas Wojo

    Sylas Wojo TDPRI Member

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    In this thread I'll be posting my Princeton 5F2a build, feel free to give me advise, tell me if I'm doing something wrong, what I could do better... Here Ill be documenting my process, so stay tuned!
     
  2. Sylas Wojo

    Sylas Wojo TDPRI Member

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    janglemore and screefer like this.
  3. King Fan

    King Fan Poster Extraordinaire

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    Impressive start, designing and drilling your own board. Never gonna criticize; only 'critique' might be to double check that layout. I still find things I’ve drawn wrong no matter how often I revise. :)
     
  4. King Fan

    King Fan Poster Extraordinaire

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  5. Preacher

    Preacher Friend of Leo's

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    @Sylas Wojo how is it working with the fiberglass? I tried one time and kept getting stuck from the edge of the fibers in the glass. Those little spinters would make my hands look like I had been stung by a couple of bees. I ended up going with Garolite which worked pretty well.

    I still have a 24" long piece of fiberglass board in the shop, did you finish the edges somehow?
     
  6. Sylas Wojo

    Sylas Wojo TDPRI Member

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    My board does have pretty rough edges too, I'd suggest a quick sanding to knock the rough edge off, and apply some epoxy or superglue to cap it off. I haven't tried this yet, but it should help.
     
  7. Sylas Wojo

    Sylas Wojo TDPRI Member

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    "Critique my 5F2a Build" , I like the sound of that better...

    How should I go about double checking the layout?

    I took a look at that power up procedure, (https://el34world.com/Forum/index.php?topic=2376.0) and I like it.
     
  8. King Fan

    King Fan Poster Extraordinaire

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    Well, check it against Rob's 5F1 where the two are the same or similar, and of course against Fender's 5F2a. Check it against as many 5F2a builds as you can find (and any really neat 5F1s). If you find differences, in a perfect world you figure out why they differ and which way is more modern or simple or safe or standard, eg why Fender used 1W dropping resistors but we use 2 or 3W.... Fun if endless journey. :)

    Especially check it against the Fender schematic. Layout details may change over the years, but the basic march of the electrons stays the same....

    Did we talk about the handy 6G10 schematic? Basically a rebranded 5F2a, and this time with *voltages.*

    Harvard schematic with voltages.jpg

    Finally, ask a ton of questions before you commit to drill, solder, wire, etc. You've done really well on that part -- the trick is to *take enough time* to 1) discuss your plans, proposed wiring, sketches, ideas, etc before you actually do 'em and 2) wait for the collective brain of TDPRI to respond!
     
  9. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Sorry. Too late for this suggestion.
    The turret location can interfere with the input jacks. Mounting further from the board edge could resolve potential trouble.
    Also, if a ground bus bar is to be used, bar interference and mounting/bracing locations must be considered.
     
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  10. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    An additional turret hear and there for potential mods can make for less headaches down the line. (such as a switchable V1 cathode cap mod)
     
  11. jchabalk

    jchabalk Tele-Meister

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    Complimentary to LowerLeft's post above (Post #9, #9, #9, ...)

    As part of laying out the turret board make sure you figure out how and where you're going to mount it to the chassis. Place it drill holes for standoffs, dry fit it and all that along with the jacks, pots, tube sockets, transformers and all that - anything that might get in the way. If you do that and make it work you'll have a much easier time with it as you populate the chassis and start working
     
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  12. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Turn me on dead man...

    o_Oo_Oo_O
     
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  13. Sylas Wojo

    Sylas Wojo TDPRI Member

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    Circuit board is all populated, and it looks like everything fits in the chassis. My plan is to follow King Fans layout pretty closely... unless I find a safer/simpler way to wire things, and mod later. But I do like the idea of adding extra turrets to make modding cleaner, safer and easier. What mods do you guys feel like I should prepare for? Adjustable negative feedback, switchable V1 cathode cap ect... is youtube a good place to start when I try to incorporate these mods into my amp?

    20201015_151623[1].jpg

    Now I'll tackle @Lowerleftcoast 's point he brought up about mounting the ground bus... And honestly I'm not totally sure what I'll do about that, right now I'm thinking about mounting it to the very top of the board with a couple zip ties, but that still has the potential to get bumped and short, any suggestions?

    Oh and here's a close up of the populated board, I've only soldered 2 of the caps for now. I'd like a second check on wiring before I proceed with any other soldering. 20201014_112754[1].jpg
     
  14. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    Take a look at:
    Taking the plunge - another newbie starts his first 5E3 project.
    Discussion in 'Shock Brother's DIY Amps' started by SteadieEddie, Jun 29, 2019.

    SteadieEddie has a very nice looking bus bar that would look just as nice in a 5F2A. Note how he attaches it to the turrets.

    KingFan likes to watch the electrons on a bus. If you don't want to go to the trouble a ground wire will carry the electrons just as well. I would just use a wire but... this is your build and allowances will be made to suite your preference.
    You can listen to youtube but there are not many mods you will likely do to your 5F2A.

    An extra turret like KingFan's recent post for V1 cathode cap would be a good start. You could research to see if another turret would be needed for adjustable NFB.

    Other than youtube, I think you can get yours up and running and then use alligator clips to *clip in* some different values and listen for yourself.
     
  15. BigDaddy23

    BigDaddy23 Tele-Holic

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    Looking good, mate! These are a super little circuit. A couple of observations from my POV.

    The ground runner that links the negative side of your power filtering caps would be better wrapped around the turrets for the 2nd and 4th caps. At these points, it looks like the lead is running adjacent to the turret rather than wrapping 360deg and continuing on....it may just be the pic though.

    The only other consideration is the position of your power dropping resistors - consider how you are going to run your plate/screen/OT center tap to those turrets. The get pretty busy so poking some up through the bottom of the board and or wrapping the turret needs prior planning. Perhaps pulling them out a touch to the edge of the board will give you some more space. Same goes for the resistor strapped around the first cap - pull it down into the space between the 2 filter caps a little so it has good space between the body of the caps.

    With regard to the bus - LLC has given you some good advice. Have a good read of the threads and go with what you think will work. Personally, I like ground buses. I've made them by twisting 2 pieces of tinned copper solid (like what you have running between your caps) which I then run solder onto to solidify it. There are some good threads on grounding principles on the forum.....It can be a bit of a rabbit hole but there are plenty of learned folks here that will help you understand it. Here's one I started.
    https://www.tdpri.com/threads/blackvibe-6v6-layout-grounding-thoughts.1048723/

    Also look at some of @King Fan 's builds - he has a good way of implementing the single ground bus principle.
     
  16. Sylas Wojo

    Sylas Wojo TDPRI Member

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    I think I'll try what SteadieEddie did for his bus bar. Either that or @BigDaddy23 's 2 bus bar trick he described above
    https://www.tdpri.com/threads/taking-the-plunge-another-newbie-starts-his-first-5e3-project.959201/

    I only have 2 turrets left, so Ill leave it hanging as he did, if it is not stiff enough then maybe Ill think about a way to secure the bus bar to the circuit board.

    I'll use an extra turret for the v1 cathode cap mod for now. How does the amp's sound change when the v1 cathode cap value is changed?... Well I guess that's the point of the mod, to hear how the amp changes. Where are the v1 cathode caps located, is that my Mallory 150's?


    @BigDaddy23 , yes my bus bar (from filter caps 1-3) is not wrapped around the 2nd cap, I guess I should wrap that 360 degrees to ensure a good connection. Although cap 4 is going to be grounded separately to the unified ground bus according to @King Fan 's layout. And I'm curious as to why that would be any different then to wire that directly to filter caps 1-2-3, and what was King Fan's reasoning for then jumpering the negative side of filter cap 3 to the output cathode bypass section, rather than grounding the output cathode cap & resistor directly to the unified bus bar?

    I'll move around those resistors a bit more to have them spaced out better. I'm also thinking of routing most of the tube socket to filter cap wires under the board, and soldering them to the bottom of the turrets. But I'll see what I can come up with.
     
  17. BigDaddy23

    BigDaddy23 Tele-Holic

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    The grounding principle is to have the specific circuit section (eg preamp, phase inverter, power amp) ground as close as possible to their respective power supply filter cap (on the bus bar). That bus bar then has a single ground point (eg input jack ground tab or ground lug on chassis). The center tap for the power transformer goes to the negative end of the first filter cap.

    Have another read of the thread I linked above where I was asking similar questions to get my layout right. For securing your bus bar, another option is to use a couple solder tags screwed to your board....this is what King Fan does with many of his build. Check out some pics in his threads and it will make sense.

    I would advise you try to secure that bar at 2-3 points rather than have it floating in the chassis - otherwise you may end up with broken connections after a while. 90% of the build is in the planning. I reckon the remaining 10% is the actual physical build....it goes fast IME. Now's the time to do that, pump the brakes if you know what I mean. The last thing you want is to have to make changes after it is built.
     
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  18. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    The standard 25uF cathode cap will allow pretty much all frequencies to be amplified by the tube. The amp may have a lot of bass which is not needed for guitar. A smaller cap will not allow some of the bass frequencies to be amplified. Reducing bass frequencies can be very beneficial with humbuckers or if the amp farts out at volume. I think King Fan ended up with a 2.2uF cap there. Smaller cathode cap values range from .47uF to 10uF.
    It is the cap that is all the way to the input side (right) on your board.
     
  19. Sylas Wojo

    Sylas Wojo TDPRI Member

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    Thanks for all of the helpful replies so far... I've updated the circuit board to include some of the suggestions LLC and BigDaddy23 have made.
    20201017_114725[1].jpg

    I had to extend 2 of the resistor wires with some bus bar. I guess I should have spaced some of those turrets a big differently.
    I think I'll use those solder tags to support the bus bar. I'm still trying to figure out what position (of the solder tags) would be optimal.. Any thoughts?

    I have a wire going from the b+3 preamp filter cap to the v1 load resistors routed underneath, would it be a good idea to re position that to the top for easier maintenance?
     
  20. Sylas Wojo

    Sylas Wojo TDPRI Member

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