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UL Bassman Mods

Discussion in 'Shock Brother's DIY Amps' started by Fred Mertz, Jun 17, 2016.

  1. Fred Mertz

    Fred Mertz Tele-Afflicted

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    I would use the the Basssman 70 layout with the TMB control on the Normal channel from the Bassman 10 schematic. I would also use a 10K pot on the Bass channel instead of the 8K2 resistor. But that's your call as to what you prefer. If you were to not use the mid pots. You could replace them with 250K pots to use as gain controls for the third gain stages. FWIW, the tone stack on the Normal channel of the Bassman 70 schematic is a copy of the CP103 tone stack as found in "The Who" amp.
     
  2. andyfromdenver

    andyfromdenver Friend of Leo's

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    oh fart, I missed the combined "A" node you pointed out Commodore, probably cause I was switching back and forth between so much stuff.
    hm, I'm a bit confused as to all that is desired now :). The R&D creep is setting in. Fred, I gotcha on the voltage string, I'll have to rework the layout I started, but for the better. So If the Bass chnl I showed looks good (cept the power string changes) say "aye" lol, and then you guys say what is ideal for the fun chnl and I'll whip that up :). Standard Fender stack style? or try the scheme from the Bassman 10, which Fred are the scheme and layout inconsistent on that chnl?

    haha! confusion and chaos and hopefully resolution.
     
  3. Commodore 64

    Commodore 64 Friend of Leo's

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    I'm looking for a Traditional Fender TMB on one channel (which is the one on the Normal Channel of the Fred's Bassman 10 schem + a triode gain stage) and the CP103 on the other (which is the one on the Normal Channel of FM's last Bassman 70 schem).

    Clear as mud? LoL. Can't thank you both enough for doing this!
     
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  4. andyfromdenver

    andyfromdenver Friend of Leo's

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    Fred ;-) et al, what do you think of this for the "Normal chnl"? It uses the mid and the deep controls still. I separated out the V1B cathode components for clarity, and we will get the power for the 3rd triode from a new source as mentioned. A thought, if V1B had a 1500 and a 25uf hanging off the cathode instead, one could wire the simplified paralleling at least once on the tidy layout. But of course it's easy enough to keep separate, to keep V1B partially bypassed.

    I Hope it's not presumptuous that I am adding to the thread, Fred.
    Take care[​IMG]
     
    Last edited: Jun 29, 2016
  5. Commodore 64

    Commodore 64 Friend of Leo's

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    Looks good to me, Andy!

    And since this is an eyelet build, if something needs tweaking, it's little trouble. So whatever you want to go with, I'm comfortable building.
     
  6. Fred Mertz

    Fred Mertz Tele-Afflicted

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    Hi Andy. You are more than welcome to share your ideas in this thread. These UL amps are great platforms for modding. One could even come up with an AC50 channel, if one had a mind to.;)

    Splitting out the cathodes would be preferable. The only reason that I didn't was because I was trying to re-purpose the existing circuit board. V1B and V2B shared a common cathode resistor and by-pass capacitor on the original board. The 1K ohm and 2.2 uf combination is a compromise between the Hiwatt and Bassman circuits. This is an area where one could tune the frequency response of the amplifier to suite their taste. The 1K5 and 2 uf combination would be a good starting point.

    Things are starting to settle down here. I started on a board in DIY Layout editor last night. I'll see if I can finish it up in the next couple of evenings.
     
  7. andyfromdenver

    andyfromdenver Friend of Leo's

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    cool guys! Well, I will leave this bad boy to you Fred :)

    if I add one here, it will be my 4 tube
    normal fender bass channel (I call it "keyboard" channel in my mind), and a vox channel with cathode follower top boost, mixer, ltp, maybe no master vol (though anyone can throw one in, and come to think of it, it might be more apropos to mix into the LTP triodes)
    this will be for people with a treb, bass, deep sw, bri sw bassman 70 or silverface bassman.
     
    Last edited: Jun 30, 2016
  8. Commodore 64

    Commodore 64 Friend of Leo's

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    http://www.valvewizard.co.uk/smoothing.html

    Merlin says I should use 227k (if my math is right) for voltage sharing on the series caps (220uf) in the first stage. Fender used 100k, and so did I. Should I replace with 220k?
     
  9. Commodore 64

    Commodore 64 Friend of Leo's

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  10. Fred Mertz

    Fred Mertz Tele-Afflicted

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    It really doesn't matter. The 220 uf 220K combination yields a cut-off frequency of .003 hz vs .007 hz for the 220 uf 100K combination. By the way, I think it would be a good idea to wire in ceramic capacitors parallel to the diodes. Fender used .002 uf 1,000 volt. Merlin recommends .01 to .1 uf.

    The cabinet looks great.

    My mother was hospitalized last week and I've been at the hospital most of the week.
     
  11. Commodore 64

    Commodore 64 Friend of Leo's

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    FM, best wishes to you and your mom. Been through that, hope your outcome is better than mine was.

    I have a good stock of 100pF discs, but no others, so I'll lay in a bunch of .01uF. Need to do a mouser order anyways for bypass caps...
     
  12. andyfromdenver

    andyfromdenver Friend of Leo's

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    wishing you and your family moments of peace.
     
  13. Commodore 64

    Commodore 64 Friend of Leo's

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    Ceramic caps on the way.

    On a tangentially related note: I gigged the 4x10 cab with MOD 10-35. Have to say I didn't like it very much. I did play music through them for 24 hours before the gig (hoping to break 'em in a little), but I just wasn't digging what I was hearing. Head I used was an EL34 self-split circuit.

    I usually use a 2x10 (G10 Gold, G10 Greenback) or 1x12 (G12 Gold). I'll have to give this some more break-in time, and some "me learning" time on how to tweak my amp, pedals, etc...
     
  14. Commodore 64

    Commodore 64 Friend of Leo's

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    So, now that I've disassembled the original circuit...I think I have need for a...bass amp. Working with a local struggling bar, we are going to do Open Jam Thurdays. I'm going to backline some of the amps I've built, so people can play 'em. And we will need a bass amp. I have the original 4x10 carcass of the Bassman, which is loaded with Carvin 10s.

    So, i'd like to build a simple bass amp, with a line out. Kinda like what was in here before.
     
  15. jonrpick

    jonrpick Friend of Leo's

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    Not to hijack... but where has Fred been? Haven't seen him online in quite a while.
     
  16. Commodore 64

    Commodore 64 Friend of Leo's

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    Yeah that was part of the reason I resurrected this. I'd like to build out a nice bass amp in this carcass, using the iron and chassis. Just not sure what to do about the circuit. Was thinking I might try 6550, since some people have indicated the PT between the Bassman 70 and the Bassman 135 are the same. I wonder if the OT is as well? In which case, maybe just do a quad of 6l6.
     
  17. Commodore 64

    Commodore 64 Friend of Leo's

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    OK I'm trying to take Fred's latest Bassman 10 layout, and add a gain stage to each channel. I'm using DIYLC, and the program is nice, but I'm in over my head I think. If anyone wants the .diy file, just PM me.

    Another option would be to take Fred's Bassman 70 Schematic, do a layout of that. I need to take a break, and reassess the best way forward here.

    [​IMG]
     
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  18. jonrpick

    jonrpick Friend of Leo's

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    Ha... I have nothing to contribute other than at this exact moment I'm currently using DIYLC to lay out an amp on Veroboard. A tube amp. Foolish?

    It'll look clean, and may just put on a great light show! :D
     
  19. Commodore 64

    Commodore 64 Friend of Leo's

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    OK everyone. I've completed a layout based on Fred Mertz's Bassman 10 Mods. Fred disappeared, hope he's OK, so I've picked up the mantle of making a layout from his ruminations. Of course, once verified, this is what I plan to build in my '79 Bassman 10 (UL) carcass.

    Off the top of my head, things to check that weren't on FM's layout:

    1. Check the TMB on the AA864 Channel. I tried to adapt it from a fixed 8.2k resistor (FM's layout) to a pot.
    2. Added a gain stage to AA864 Channel
    3. Added a gain stage after HiWatt Channel
    4. I changed the voltage multiplying power supply to a more traditional bridge rectifier set up. The PT is a 360V (180-180)non-centertapped.
    5. Bypass and coupling caps in the extra gain stages, I just guessed at values.


    Anyone willing to review this for me?

    PS: DIYLC seems to be easy and awesome. If anyone wants my .DIY file let me know. Link to DIYLC: http://diy-fever.com/software/diylc/
     

    Attached Files:

    Last edited: Mar 5, 2017
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  20. ChopSauce

    ChopSauce Tele-Meister

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    I don't know much about the Bassman but I'm surprised that the fuse appears on the neutral, rather than on the live.
     
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