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The Build Commences...

Discussion in 'Shock Brother's DIY Amps' started by shortcircuit, Jun 14, 2018.

  1. shortcircuit

    shortcircuit TDPRI Member

    82
    Sep 9, 2017
    North Carolina
    Chassis.JPG

    There's a 5Y3 and a 6V6GT, single-ended. A cathode follower will be driving a tone stack ripped off from the AB763. Feel free to speculate as to the rest of the build.
     
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  2. shortcircuit

    shortcircuit TDPRI Member

    82
    Sep 9, 2017
    North Carolina
    Heater.jpg

    Filaments wired up. The wire is 20 AWG nickel plated fluoropolymer insulated twisted pair, supposedly specced for the ISS....yea.
     

  3. shortcircuit

    shortcircuit TDPRI Member

    82
    Sep 9, 2017
    North Carolina
    Indicator Light - 1.JPG

    The window for the indicator light is a 3/8" hole filled with epoxy mixed with small bits of aluminum (from drilling the holes) and graphite powder (scraped from pencil lead). You can see the blue painter's tape through the lower bolt hole.

    Indicator Light - 2.JPG Indicator Light - 3.JPG

    The indicator light runs off the 6.3V filament tap, full wave rectification with 1N914's and a capacitor so that when I turn off the amp, the LED fades out like an incandescent bulb. This is a true sign of a diseased mind.
     

  4. shortcircuit

    shortcircuit TDPRI Member

    82
    Sep 9, 2017
    North Carolina
    PS-1.JPG PS-2.JPG

    My standard power supply built on a cut down piece of a turret board. The 2 47uF caps are Panasonic's. All three are rated for 105 degrees C and 10,000 hours. Can't get that in axial caps. The single turret is for the voltage divider for the elevated filament supply because of the cathode follower.
     
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  5. shortcircuit

    shortcircuit TDPRI Member

    82
    Sep 9, 2017
    North Carolina
    Tubes.JPG

    From left to right: 1st preamp tube, 2nd preamp tube (I also have a glass version), 6V6GT, 5Y3.
     
    Last edited: Jun 15, 2018
    Nickfl and Jake Nelson like this.

  6. shortcircuit

    shortcircuit TDPRI Member

    82
    Sep 9, 2017
    North Carolina
    Preamp.jpg

    The preamp...she is done. In case if anyone is wondering, the film caps are not generic brown boogers. They are Matsushita/Panasonic polyester caps (but still dirt cheap). See the "M" logo below.

    Matsushita.JPG
     
    Last edited: Jun 15, 2018
    Inglese, CoyotesGator and robrob like this.

  7. bigguy12321

    bigguy12321 Tele-Meister

    307
    Jul 13, 2012
    Traverse City Mi.
    Now I know why the dogs are dancing in the morning to go outside. EXCITED. EXCITED, EXCITED!!!

    Beautiful work Shortcir! I don't have any idea what it will be but I can't wait.

    Do you have any pics of the underside of your capacitor board? I would like to see how the stand-off's look. (probably just as neat as the rest)

    Thanks!

    a
     

  8. shortcircuit

    shortcircuit TDPRI Member

    82
    Sep 9, 2017
    North Carolina
    PS-3.JPG

    Nothing special. I used a small round file to get the holes to fit the leads. After soldering, I hot-snotted the caps for extra support. The scrape marks on the top two empty holes were from me yanking out the turrets.
     
    Last edited: Jun 15, 2018

  9. shortcircuit

    shortcircuit TDPRI Member

    82
    Sep 9, 2017
    North Carolina
    PS in.jpg

    Power amp wired up. No cathode resistor yet. I got a bunch of 5W resistors from 360 ohm to 560 ohm to test to set the final bias. The power supply is in, and the voltage divider for the elevated heater supply is wired up. Also, the 2 protection diodes (UF4007) are in place.
     

  10. bigguy12321

    bigguy12321 Tele-Meister

    307
    Jul 13, 2012
    Traverse City Mi.
    Thanks! And that's the underside of the board... Sheesh!!!
    I have got to step up my game. This inspires me.

    a
     

  11. flyswatter

    flyswatter Friend of Leo's

    Jan 12, 2013
    Quebec
    Nice work! I like the way you use those little handcut turret boards to tame the necessary connections and provide a good hybrid between true p2p and turret-mounted components.
     

  12. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    Very nice point-to-point work. Looking forward to fire-up.
     

  13. shortcircuit

    shortcircuit TDPRI Member

    82
    Sep 9, 2017
    North Carolina
    Finished except K resistor.jpg

    Got back from a weekend get-away with the missus. Finished up the wiring. I clipped in a 560 ohm resistor for the 6V6 to be on the safe side. With the power tube I had in there, it was dissipating about 10W. Nice clean sound, but I haven't cranked it up as it is late. It turned out that I didn't need any resistors for the filament (it's at 6.45V), so I jumped the turrents with copper wires. Tomorrow, I will play with the bias for the power tube. The schematic is as below. Nothing too nutty, but I'm planning a push-pull version with a 6SN7 as a LTP phase inverter.

    Sch.jpg

    Oops, the grid stopper for the 6V6 should be 1K5. I also got the B+ coming out of the wrong node. You guys/gals know where it should go.
     
    Last edited: Jun 18, 2018
    kleydejong, CoyotesGator and Nickfl like this.

  14. shortcircuit

    shortcircuit TDPRI Member

    82
    Sep 9, 2017
    North Carolina
    I spent the last couple of days playing with the little guy. First, I measured the plate and screen currents of all of my 6V6 and 6P6S tubes. I settled on 470 ohm as the cathode resistor, giving me a plate dissipation of 10.6 W and keeping the plate voltage above 300 V. After running the amp a bit, I remeasured the voltages, and the 6.3 V rail had crept up to 6.54 V, so I soldered in two 0.1 ohm resistors, bringing the voltage down to 6.33 V.

    04 Overall.jpg

    The 6SJ7 tube was a bit microphonic, but it did not cause too much trouble as the chassis was mounted on a piece of plywood with rubber isolating feet. I had gotten a pair of 6SJ7WGT from ebay and tried them. The one that worked was also a bit microphonic. The other one was dead. The filament was open. The tubes were supposed to be NOS, and visually were in excellent shape. I carefully took off the metal shield and everything looked good. I reflowed and added some solder on pins 2 and 7, and voila, it came back to life. I couldn't get the metal shield back on tight enough so it rattled a bit. I glued it down with a generous amount of high temperature RTV silicone adhesive. After the glue set, I cleaned up the tube and plugged it in. No more microphonics! The silicone adhesive must have acted as a dampener.

    05 Outside.jpg

    I think I'll change the LED to a red one to match the switch cover.

    The amp sounds nice and twangy. It's reminiscent of some of the older amps demonstrated by Uncle Doug in his videos. When the gain and the volume are cranked, the amp breaks up nicely with a fuzz tone that sounds a bit like the germanium Fuzz Face that I'd built.

    I tried a set of Soviet tubes--6N9S, 6J7, and a 6P6S. The 6J7 was also somewhat microphonic, but better than its American counterpart. The overall sound with the Soviet tubes was a bit bright with a glassy edge to it. I prefer the warmer American tubes.

    Here is the corrected schematic:

    OctalSE.jpg

    Now on to the next build!

    0620182356.jpg
     
    Last edited: Jun 21, 2018
    CoyotesGator, robrob and D'tar like this.

  15. D'tar

    D'tar Tele-Afflicted

    Jan 11, 2013
    WNY
    @shortcircuit

    That's a fine little amp right there! Excellent job! I would love to hear it.
     

  16. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    That is a beautiful amp, inside and out. I love the covered safety switch. Your photography is also top-notch.
     
    Last edited: Jun 21, 2018

  17. LudwigvonBirk

    LudwigvonBirk Tele-Holic

    Age:
    116
    561
    Aug 26, 2017
    Madison
    Looks super nice, well done.

    Suggestion (safety thing): add a grommet to the PT hole.

    upload_2018-6-21_9-51-34.png
     
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  18. Preacher

    Preacher Friend of Leo's

    Apr 17, 2007
    Big D
    Brings back memories eh? I love it as well! Has that Top Gun look to it!
     
    robrob likes this.

  19. robrob

    robrob Poster Extraordinaire Ad Free Member

    Dec 29, 2012
    United States
    ^Good catch Ludwig, a grommet is definitely needed there.
     

  20. LudwigvonBirk

    LudwigvonBirk Tele-Holic

    Age:
    116
    561
    Aug 26, 2017
    Madison
    Also (again safety thing): I would suggest adding a drop of Loctite to the nuts. Maybe you already have and it isn't visible.

    Ex: Don't want these vibrating themselves loose! :


    upload_2018-6-21_11-13-14.png

    upload_2018-6-21_11-11-24.png
     
    shortcircuit likes this.

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