Another Parts-On-Hand build... 6V6 Spitfire Reverb

Discussion in 'Shock Brother's DIY Amps' started by RollingBender, Aug 3, 2019.

  1. RollingBender

    RollingBender Tele-Holic Vendor Member

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    Mocked up and ready to start modeling the chassis for a 2-6V6 power / Matchless Spitfire preamp / 1-tube reverb combo.

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    The PT is from an old radio (if I remember correctly). It is another 110v so will need a bucking transformer to keep voltages where they need to be. At 110VAC input, it puts out 330-0-330VAC and normal voltage at the heaters. The choke, impedance selector switch and tube sockets come from a Hammond AO-15 amp. The PT is from a mystery push-pull 6V6 power amp, tests at 8K primary and has 4, 8, and 16 ohm secondary taps. I’ll be using a reverb tank harvested from a Hammond organ but will need to purchase a reverb transformer in order to complete the project.

    I’ll be carving the chassis out of the 2” X 5”, 1/8” wall tubing shown in the mock-up. I’ll try to be more diligent at photo documentation of this process. The first one I did this way turned out great.
    https://www.tdpri.com/threads/junk-pile-build-the-“champlifire”.964902/

    Wish me luck!
     
    Last edited: Aug 3, 2019
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  2. Mudman32

    Mudman32 Tele-Meister

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    Good luck!
     
  3. RollingBender

    RollingBender Tele-Holic Vendor Member

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    End caps for chassis on the mill.
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    I made these to tight tolerance so I will need to pound them into place on the end of the chassis. The front, back, and bottom will have small screws to secure it in place but I will do all the drilling and tapping on the mill as I cut the features into each side.
    C8ABB35C-B64A-45D5-91CD-A9E753B02693.jpeg

    The chunks left over in the two corners are where I will drill and tap for chassis mounting screws. This is not the best grade aluminum so I want to have a lot of thread engagement.
     

    Attached Files:

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  4. RollingBender

    RollingBender Tele-Holic Vendor Member

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    Way down inside...
    583C3180-5D09-4209-803B-394697C19AB8.jpeg

    End caps pressed into place.
    6E16EB96-63D9-43E9-AE9C-484862AA1620.jpeg
     
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  5. RollingBender

    RollingBender Tele-Holic Vendor Member

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    Back panel holes and engraving done. Right now, it does a fair job at retaining fluid. You can see it’s full.
    EDC143AC-9C7E-432D-BD05-7FD3E051FEB2.jpeg
     
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  6. RollingBender

    RollingBender Tele-Holic Vendor Member

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    Bottom side before...
    5A9556A6-8866-4189-9941-16A0D48FD6FC.jpeg

    ...and after a joy-ride in the milling machine...

    4D7EA4A7-3D4B-4A88-AE62-9960664E2041.jpeg
     
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  7. RollingBender

    RollingBender Tele-Holic Vendor Member

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    Front panel before....

    4A199095-D451-4309-B338-58E7A1ED4B10.jpeg

    ...and after.

    3EDB8A24-A360-493C-8CB2-9121BFB338C4.jpeg

    On the front and back panels where I am doing engraving, I run a 2” shell mill along the surface to make it perfectly flat. If it’s not flat, the engraving won’t be even. Just for fun, I put my logo on the front faceplate.

    I also re-named a couple controls. Instead of “Volume” and “Master”, I labeled them “Gain” and “Volume”. Even though I won’t have much gain (dirt) on this amp, that is how those controls will actually be used.
     
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  8. RollingBender

    RollingBender Tele-Holic Vendor Member

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    The final side, the top, before...

    22CF84DB-356A-4478-A495-DEA69B3842EE.jpeg

    ...and after...

    A9EBB4C8-7934-4560-810D-D7D100E853EA.jpeg

    Those end caps I made first not only keep fingers out and complete the Faraday cage, they also provide support, something solid to clamp down on in the mill vices. Without them, I would need to be extra careful not to crush the chassis, especially on this last operation where I’m removing such a large bit of structure. On the other hand, the walls of this chassis are about 3X thicker than your standard bent sheet metal chassis. Might not be bullet proof but should stop about any BB gun out there

    6E73B2BC-8900-4201-8A70-2B7C8D7FF37A.jpeg

    Before the last operation, I discovered that I didn’t have a sharp version of the proper drill bit or tap for the chassis mounting bolt holes so a trip to the hardware store is on the agenda for tomorrow.
     
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  9. tubelectron

    tubelectron Tele-Meister

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    Ah, yes ! The chassis is machined, not sheet-metal worked ! :eek::eek::eek:

    You are building a 5000 meters parachute proof amplifier...:D

    Just for my curiosity : i'd like to know the weight of your finished bare chassis.;)

    That said, congratulations ! :cool::cool::cool:

    -tbln
     
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  10. RollingBender

    RollingBender Tele-Holic Vendor Member

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    Finished bare chassis weight...

    EE9A4473-12C2-4EFF-986A-ADB1BE9AFF5E.jpeg
     
  11. RollingBender

    RollingBender Tele-Holic Vendor Member

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    And this is why you buy quality tools and not the crap from the hardware store.

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  12. RollingBender

    RollingBender Tele-Holic Vendor Member

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    The above pic was of a broken tap sunk about 3/4” into the hole that snapped while power tapping in the machine.

    I milled a notch sideways through the tubing up to the tap, removed the 4 retaining screws and knocked the end piece out. I then made a new end cap and installed it and re-drilled and tapped all the holes except for those 4 larger mounting bolt holes. I’ll hand tap those later.

    Here’s the repaired product. It will never be seen once the chassis is installed and nothing has been made weaker by the repair.

    BA338E30-76C1-412B-8207-AFC79E4B52D0.jpeg
     
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  13. RollingBender

    RollingBender Tele-Holic Vendor Member

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    Chassis completed! Ready to start filling it up with parts.

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  14. RollingBender

    RollingBender Tele-Holic Vendor Member

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    Well, that didn’t work.

    I started assembling the parts and discovered some unforeseen interference between the impedance selector switch and one of the tube socket pins. The speaker and reverb jacks were uncomfortably close to tube socket pins also. I think I can move the tubes a bit to fix this.

    Plus.... I forgot to make a hole for the choke wires and none of my rubber grommets fit this thicker material. I’ll make a countersink on each hole where wires pass through so the grommets will essentially have a thinner wall to be on.

    Plus... I couldn’t get the PT in because the wires wouldn’t go in before the mounting bolts needed to line up. A small cut-out will fix that.

    Back to tweak the model and then cut a new chassis. I should be able to re-use the end caps, so I have that going for me.
     
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  15. JuneauMike

    JuneauMike Friend of Leo's

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    Dude, you are on fire!

    Is that chassis made from aluminum channel stock?
     
  16. tele_savales

    tele_savales Tele-Meister

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    Looks like you're going to have to start over.
     
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  17. RollingBender

    RollingBender Tele-Holic Vendor Member

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    Ha,ha....took me a bit to catch the pun.

    The chassis is made from 2”x5”x 0.150” wall aluminum rectangle tubing.

    The first chassis above is being scrapped and a new one goes on the mill this evening with the listed modifications.
     
  18. RollingBender

    RollingBender Tele-Holic Vendor Member

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    Now everything fits!!!....so far.

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    Time to start making the board. I need to open my first Spitfire Reverb up to confirm all of the one-tube reverb circuitry before I map it out for the CNC.
     
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  19. JuneauMike

    JuneauMike Friend of Leo's

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    Cheapskate Leo would throw a slide rule at you if he saw that chassis leave his shop. But I'm lovin' it.


    proxy.duckduckgo.jpg
     
  20. RollingBender

    RollingBender Tele-Holic Vendor Member

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    Here’s how I drill my boards...

    Cut board to size then cover with masking tape. Glue taped board to taped fixture plate with super glue.
    1E28D41F-C337-4104-AE4A-0F39F6A95FAD.jpeg
    Then I push a button!


    (Time lapse. Actual time of what is seen in the video is about 2:15)

    Then I heat up the fixture plate with a torch to loosen up the tape and pop the board free.

    Here it is!
    B63AE1FC-780E-43FE-89FD-250D66E30395.jpeg
     
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