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Seems like I’m doing this backwards...

Discussion in 'Shock Brother's DIY Amps' started by RollingBender, Mar 29, 2020.

  1. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    There’s a lot of test fitting going on with this build. Some (all) parts are going to be a huge pain to wire.
    B880F02A-8F5D-4F20-AC2F-ADC7E27A5A64.jpeg
     
  2. BigDaddy23

    BigDaddy23 Tele-Holic

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    I reckon you need at least 2 more pots :lol:
     
  3. kbold

    kbold Tele-Afflicted

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    Yep ... with test points for bias adjustment.

    Probably better to wire up before fitting tubes.:lol::lol::lol:
     
  4. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    There’s one on the lower left of the chassis pointing down. It’s the bias pot. That one is going to be a bugger to solder. I can remove the end cap to get at it from a different angle though.
     
  5. Kevin Wolfe

    Kevin Wolfe Tele-Meister

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    Very nice work so far. Should be a sweet circuit. Love the chassis. Is that an ext. speaker jack we see?
     
  6. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    That jack pointing out the back is for the reverb/trem footswitch.
     
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  7. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    Just enough room...
    C86B42A5-09A6-4C52-9A13-2E12421EFE9F.jpeg
    I did have to move the reverb driver 3/8” up.
     
  8. Mr Ridesglide

    Mr Ridesglide Friend of Leo's Silver Supporter

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    no problem!
     
  9. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    80 turrets!!!
    0FE8DCF2-B152-4253-A6A9-DA5FA7273D72.jpeg
     
  10. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    Populated and soldered...
    03365DCC-94E3-4C9B-805B-76FD34756948.jpeg
    Board is 2.25” x 12”. Stuff is crammed in there pretty tight.
     
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  11. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Nice!

    Sent from my moto g(6) using Tapatalk
     
  12. kbold

    kbold Tele-Afflicted

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    Attach wires before fitting to chassis?
     
  13. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    I usually do that but I’m worried that with the tight quarters of the chassis an the large number of hookup wires that I would have a high rate of failure (broken wires) from the wrestling match getting the board installed and moving things around into their proper position.
     
  14. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    Heaters all wired.
    Transformers and choke mounted and connected (mostly).
    Board mounted.
    Mains wired.

    Now the fun of adding all the jumpers begins!

    276F2D7F-5DFB-44FB-9B8F-87FFB64C52FC.jpeg
     
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  15. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    Well....this isn’t right....
    67A0FEF3-9683-4A2E-86BB-2CF09DB5E067.jpeg
    It makes for a cool photo though.
    Everything “works”. Just need to get it working properly.
     
  16. Lowerleftcoast

    Lowerleftcoast Friend of Leo's

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    I thought I saw the Northern Lights...

    :lol::lol::lol:
     
  17. mjcyates

    mjcyates Tele-Meister

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    Looks like you could roast some hot dogs in there!
     
  18. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    I rewired the bias circuit to match the Hoffman schematic I was using instead of the incorrect way I had it. Then I rewired it to the schematic from RobRob’s site. Then I discovered that my bias pot was faulty. I then subbed in a new pot and was able the stop the redplating and get the bias under control.

    On to the next problem(s)... there is a high pitch feedback sounding squeal that is reverb knob dependant (NFB not yet connected) and then made worse by the master volume (Trainwreck style post PI). There’s actually 2 different frequencies of howl which can be selected by carefully tweaking those two controls.

    Second issue is the massive amount of gain on tap. Clean stops at 1.5 on the volume knob and complete shutdown at 7 with a big, low chord.

    Don’t have a schematic to show but it is AB763 with....

    A one-tube reverb circuit replacing the 1.5 tube Fender circuit.

    Princeton Reverb style 1/2 tube trem circuit replacing the AB763 style roach tremolo.

    Princeton Reverb style bias circuit.

    EL84’s for power tubes (with values of other components in the power amp section changed accordingly).
     
  19. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    I thought about the reverb tank being in such close proximity to the big magnet on the speaker being the cause of some trouble but my last Spitfire type build used the same speaker, reverb circuit and tank in a similarly small box and it is dead quiet.

    I’m now suspecting some imbalance in the mixing resistor part where the reverb sends and returns to be the problem. The way I have used this one tube reverb in the last 3 amps I’ve put it in have the reverb inserted just before a LTP PI with a 100K mixing resistor. The AB763 has it inserted between the tone stack an the last gain stage with a 3.3M mixing resistor and a 10pf bypass cap. Any ideas?
     
    Last edited: Apr 24, 2020
  20. RollingBender

    RollingBender Tele-Afflicted Vendor Member

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    From RobRob’s site...
    ED0EC7DE-81EE-48AD-B059-284E19D0E568.png
    ...is 33k the correct value to match Fender’s high/low inputs?
     
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