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Yet another Dumble conversion...

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Normster, Sep 12, 2005.

  1. Normster

    Normster Member

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    I got tired of tweaking the Pignose and started ripping Loren's SF Bassman apart. ;)

    Here's the story so far...
    Bassman conversion, pictorial essay

    Mostly inspired by Gary at Glaswerks.com but with a few minor tweaks. Hopefully I'll get a chance to finish it up next week and see if any smoke leaks out. :eek:
     
  2. macula56

    macula56 Member

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    nice looking stuff Normster. if you don't mind me asking, what schematic are you working off of? jmac
     
  3. Normster

    Normster Member

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    It's basically the '77 Hybrid-A schematic with a tube reverb circuit added in place of the effects loop. Channel switching will be done via a Weber low power board. Tone stack switches will include a 500pF to 250pF treble cap switch, boost switch, and possibly a combination bright/deep switch.
     
  4. memphisrain

    memphisrain Member

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    Damn you Normster!!!

    I just decided that I would get a Zendrive and wait until I could have Fuchs do a mod on my SF Bassman, but here you are doing that to the exact same model of Bassman I have...


    G.A.S. attack......

    Where did you come up with that snazzy layout sheet that you've got under the board? And where can I get a copy of it?


    Thanks,
    mR
     
  5. glasman

    glasman Guest


    Glad to see someone looks at the site. Hmmmm, that reverb looks mighty familar. :)


    Good luck with the amp..


    BTW, what kind of tweaks? Always curious to see what others are trying.

    Gary
     
  6. Normster

    Normster Member

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    memphisrain - The diagram is in Visio format. Shoot me an email (nfeaster <at> comcast.net) and I'll mail it to you. It's not completely accurate so you'll have to use the Hybrid-A schematic on blueguitar.org to verify the switch connections.

    Gary - Your site has been a major inspiration for me. I especially like the way you mounted the relays to the board...makes for short elegant connections to critical tone circuits. This time around I'm just using a Weber channel switch board, but as you can see, I left plenty of room on the board for relays. :)

    The tweaks are mostly in the tone stack area. I'm going to be trying a few different combinations of Dumble's switching schemes to see which ones I like best.

    BTW, where did you mount the 220k grid resistor (return from tank)? I see it on your schematic but can't locate it on your board.

    Thanks,
    Norm
     
  7. glasman

    glasman Guest

    I did the same thing on my personnal amp. The treble and mid caps have three different settings available.


    Hey Norm, you discovered the missing component on the board. When I designed that version I forgot to add it to the board so I ended up putting it right at the RCA jack for the reverb return. I have since corrected this devine screw- up in later boards.

    I just drilled up 8 new boards of two different designs that I will be using in a set of amps I am currrently building. The first three amps of this set are a 20 and 50 watt that are similar to the previous amps I have built and the third is a 50 watt amp with a few (LOT) more bells and whistles.

    Gary
     
  8. TheAmpNerd

    TheAmpNerd Member

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    Now that looks like a lot of phun.

    Me thinks I could be inspired.
     
  9. Normster

    Normster Member

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    Check your mail. ;)
     
  10. scottl

    scottl Member

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    Sounds great!!! Sign me up!!! LOL

    ;)
     
  11. Normster

    Normster Member

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    Finally done!!!

    One minor wiring problem on first fire-up. (Had to reverse the OT wires.) After I fixed that, the amp just sang! I dropped it off at Loren's today and he's grinning from ear to ear. Hmmm...I wonder what I should build next? ;)
     
  12. glasman

    glasman Guest


    So how did the reverb work out?


    Gary
     
  13. Normster

    Normster Member

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    Reverb came out pretty sweet. I used a 1Meg pot (since I didn't have any 2Megs lying around) so it's very subtle, but Loren uses very little reverb anyway. It does act a little strange past 2 o'clock...like a boost circuit, but as I said, Loren doesn't use much reverb.

    After he plays it for a week or so, I'm going to get it back, install the foot switch relays, and put in the correct pot value.

    Thanks again for sharing your layout (and wisdom)!!!

    Norm
     
  14. Richard Guy

    Richard Guy Member

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  15. darkbluemurder

    darkbluemurder Member

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    Normster,

    how did you wire the Weber relay board to the switch - I am confused since it says it should connect the tip to the ring and neither of them should be grounded. Do I need an isolated stereo jack to do this?

    Any help would be greatly appreciated.

    Thanks a lot and keep on rockin'
    Darkbluemurder
     

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