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Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com
Asher Guitars WD Music Products Amplified Parts Mod Kits DIY Nordstarnd Pickups Warmoth.com

I goofed somewhere... Bassman Recap

Discussion in 'Shock Brother's DIY Amps' started by Axis29, Nov 10, 2017.

  1. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    So, I got frustrated and replaced the entire doghouse board and feed wires for B+1 and B+2.

    [​IMG]

    and then replace the three caps inside, with two:

    [​IMG]

    Seemed simple enough. I've gone over the schematics for the reissue amp and for the original 5f6-a circuit. Currently, I have basically replaced C16 and C17 (2 x 100/350 in series) with two 22/500 caps in parallel; replaced C18 and C19 (2 x 47/350) with one 22/500 cap; replaced C20 and C21 with 22/500 caps and removed C24. In the process, I have also deleted R34, R35, R36 and R37.

    My new B+1 wire runs from the junction of the first two filter caps positive to CP33 and the new B+2 wire runs from the third cap in the doghouse to CP34. This all looks correct according to all of the schematics I can find.

    Here's the schematic

    I also replaced the two ground wires from the doghouse with one and ran it to a ground bolt near the transformer as per this article on singlecoil.com

    I'm not terribly good yet at reading schematics, but I cannot find corresponding resistors in the original circuit, nor can I figure out why they should need to be there on my new board, as I have deleted both sets of series caps.

    Now, when I turn the amp on I get a steady tone, not staticky, or fluctuating, but a constant deeper tone. Not a squeal like if I had the wires reversed from the power transformer. I haven't messed with anything else.... It's loud too. Loud enough that I switch it right back off after trying. It comes on immediately.

    Any guesses?

    I've checked my solders, made sure I didn't burn the main PCB and am using the same tubes and SS rectifier that were in it when I turned it off before applying heat and pliers...
     

  2. Darkness

    Darkness Tele-Holic

    Age:
    49
    866
    Apr 7, 2016
    Stygian Gulf
    Why is the polarity of the right hand cap in the second pic reversed? Board says +/- clearly.
     

  3. D'tar

    D'tar Tele-Holic

    949
    Jan 11, 2013
    WNY
    Is that cap backwards? On the right of c24 empty slot
     

  4. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    Dagnabit. Yes, it's reversed! :(

    Crap, crap, crap!

    I hate working on PCBs that are still in the chassis! Now, I'm gonna have to tear all that crap out again... Errrrr. I'm sure in going back and forth with the PCB, I popped it in upside down. :confused:
     

  5. Darkness

    Darkness Tele-Holic

    Age:
    49
    866
    Apr 7, 2016
    Stygian Gulf
    I hope that helps. I’ve done that once before myself. Let us know. :)

    If you don’t want to tear it all back out, you can clip the leads, leaving enough for a good solder joint, and rotate the cap. Then resolder. I know this isn’t the best practice, but it will work fine if done well.
     

  6. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    I have gotten way too fast at pulling the PCB...

    [​IMG]

    The bummer is, there's still that buzz.

    So, on to the next guesses...
     

  7. Darkness

    Darkness Tele-Holic

    Age:
    49
    866
    Apr 7, 2016
    Stygian Gulf
    @muchxs you are missed man.

    Hopefully one of the other amp wizards on here will lend their sorcery knowledge. I know just enough to be dangerous. :)
     

  8. Commodore 64

    Commodore 64 Friend of Leo's Ad Free Member

    Age:
    42
    Mar 1, 2010
    Kent, OH
    edit.

    Is the choke still wired between the first 2 nodes?
     
    JD0x0 and D'tar like this.

  9. D'tar

    D'tar Tele-Holic

    949
    Jan 11, 2013
    WNY
    And B+ on points x,y,z
     

  10. JD0x0

    JD0x0 Friend of Leo's

    Age:
    27
    Feb 22, 2009
    New York
    Deep hum is because you reduced power section filtering and dropping resistance, which probably reduced suppression of 120hz hum enough to become audible. Try reverting some of your 'mods' or perhaps a higher inductance choke will tame things.
     

  11. Lonn

    Lonn Tele-Afflicted

    Age:
    55
    Dec 13, 2007
    Indiana
    I'm not feeling well. I read the title of the thread as "I pooped somewhere" :confused::p
     

  12. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    First, thanks so much for the answers so far guys!

    It should be... I didn't change where power comes from, and only consolidated the grounds. In the original 5f6-a circuit, the grounds are connected through the dog house cover to the chassis.

    I'll be honest, I haven't checked voltages as the noise is quite loud.

    Okay, I'll try this. My guess is it is the dropping resistors... Just not sure how to reintroduce them yet. Gonna have to do some reading.

    Regarding reduced filtering - I actually only reduced the first filter stage by 6 uF (2 x 100 in series = 50, 2 x 22 in parallel = 44). The second stage went down by a somewhat similar number, 1.5 uF (2x47=23.5 vs. 22). The third stage was the big jump by removing the one 22 uF cap. The original 5f6-a circuit uses two 20 uF caps for the first filter, and 20 uf caps for the rest. Looking over the rest of the circuit, there aren't a lot of differences. A few value differences, but I guess the transformers are different...

    I guess I need to stop thinking of the Reissue in terms of the original circuit. At least until I understand amps better.
     

  13. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    LOL
     

  14. tubeswell

    tubeswell Friend of Leo's

    Jul 1, 2008
    NZ
    The grounding is designed to work in the Bassman RI and Bassman LTD the way that it was constructed at the factory. Which is different to a vintage amp. You're best to either reconstruct the entire amp, including ground returns the vintage way, or leave the construction as per the RI, and just change the components.
     
    Last edited: Nov 11, 2017

  15. Nickfl

    Nickfl Tele-Holic

    684
    May 24, 2016
    Florida
    Are you using a lightbulb limiter? It's always a good idea but even more so when you are changing the circuit and especially on a pcb amp where it's easier to make mistakes. It sucks to lose a transformer to a short when a lightbulb could have saved it...
     

  16. RLee77

    RLee77 Friend of Leo's

    May 15, 2016
    Silicon Valley
    I would not reuse the cap that was installed backwards. You powered on a few times, maybe several, right? That may have damaged the cap. Me, I wouldn't want it in there after that.
    Also, why did you remove c24, instead of replacing it? You halved the filtering of the highest gain stage in the amp; I'd be surprised if that didn't raise the noise level.
    Removing the series balancing resistors is fine, that will have no effect on anything. Changing the ground path of the high current section of the supply could possibly cause issues, but hard to know without seeing it.
     
    Thin69 likes this.

  17. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    I did reuse it... being lazy. I have extras (on purpose, because I know me).

    I removed C24 because I've read about it in a few places online.

    I also changed the ground scheme after reading it online.


    So, now I have conflicting reports... are they balancing resistors or are they dropping resistors? I initially thought they were balancing resistors.



    And thanks for sticking with me guys. I swear I am trying to learn while screwing up my own crap. LOL
     

  18. dsutton24

    dsutton24 Poster Extraordinaire Gold Supporter

    Dec 29, 2010
    Illinois
    If they're across caps that are in series, they're balancing resistors, see R36 and R37. If they're in series with the B+ rail, they're dropping resistors, see R38.
     

  19. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    Okay, then I only deleted the balancing resistors, not the dropping resistors.

    I haven't messed with it. The honey-do list is long...
     

  20. Axis29

    Axis29 Poster Extraordinaire Ad Free Member

    Jan 2, 2007
    Virginia, USA
    Ok, so before returning to my amp and just fiddling with it willy nilly, I've been obsessing about it in my head and looking at the schematic. I am now pretty sure now that the resistors I deleted were just balancing resistors and don't need to be replaced.

    The one mod I am unsure about currently is the ground. The article on SingleCoil.com said to replace the two black wires from the cap board with one ground wire. But, if I look at the schematic the negative ends of the caps are connected to the red/yellow wire coming out of the transformer. Am I missing something?
     

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