5f11 upgrades

Discussion in 'Shock Brother's DIY Amps' started by Mark the Moose, Jun 12, 2019.

  1. Mark the Moose

    Mark the Moose Tele-Meister

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    Last winter I built a 5f11 kit from mojotone, and built my own pine cabinet. Great amp. I’m finally getting around to the tweed covering so it’s all disassembled in my basement. While it’s opened up, I thought I might make a few upgrades. Going to install a bias pot for sure. What do you think about upgrading the OT? Allen or classic tone...is it worth doing? Also considering a master volume like Robinette posted for the 5e3, worth doing? I play a lot early in the morning before the house is up, thought it might let me drive the preamp a little harder. Any other changes I should consider?
     
  2. schmee

    schmee Poster Extraordinaire

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    I dont think an OT will change anything. Unless you want to go bigger to a non 5F11 OT. MV wasted on low wattage amps to me. But if you play at home and dont mind, or want, more breakup, might be worth it.
     
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  3. JuneauMike

    JuneauMike Friend of Leo's

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    That amp is perfect the way it is, says an anonymous guy on the internet. Don't mess with it (except for the adjustable fixed bias, that's more of a user-friendly mod).
     
  4. jhundt

    jhundt Doctor of Teleocity

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    I would only upgrade something if I had felt/found a need to do so.

    Have you considered buying a small headphone amp for your early-morning sessions? These are quite highly regarded:
    https://www.voxamps.com/headphone

    I too built a Mojo 5f11 kit. I can't imagine anything that I would do to it would make it sound any better.
     
  5. Mark the Moose

    Mark the Moose Tele-Meister

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    The only tonal changes I might make are a little tighter bottom end and earlier breakup.
     
  6. jhundt

    jhundt Doctor of Teleocity

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    I can understand that. Tighter low-end is what Fender tried to achieve with the 5f11, compared to the 5e3. I don't know how much tighter you can get it on a 15-watt tweed amp before it starts getting sterile. Have you considered a solid-state rectifier?

    As far as earlier breakup - Fender amps just don't do that. I spent years looking for that; by the time I figured this out, I no longer wanted it. I keep a little pedal handy; for home use it is a copy of a Barber Gain Changer. I keep it on most of the time. It adds the 'zing' that you might be looking for.

    In my experience, you will not be able to add that extra boost, brightness, clarity, and touch of overdrive with the tubes and circuitry available. Turning the amp up to 12 might help, though!
     
  7. Mark the Moose

    Mark the Moose Tele-Meister

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    Yeah, I've built a couple dozen overdrive pedals. Pedals are great and very practical on a gig, but there is something magical about an overdriven amp. Maybe the next amp build should be something with a front end gain control.
     
  8. jhundt

    jhundt Doctor of Teleocity

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    I built something like a Matchless Spitfire. It's like a Vox AC-30 but 15 watts. The Matchless design had a single 12ax7 at the input; but the two halves of the tube were wired in parallel. I never felt or heard any advantage to that design. Later a re-wired the amp so that the two halves of the 12ax7 were in series, with a volume control between them. Nothing really new, or creative in the design; just what Boogie was doing back in the 80's. But it works very well. It's just a gain stage added before the normal input. It gives you all the power you need at the input to push the normal first-stage a bit, just like using a pedal.
     
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  9. Mark the Moose

    Mark the Moose Tele-Meister

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    That sounds cool, do you have a schematic or layout you can post? Choice of trannys?
     
  10. JuneauMike

    JuneauMike Friend of Leo's

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    While you are waiting for a reply, there are a couple of Spitfire schematics floating around here. But the Spitfire schematics have some controversy around them (authenticity). The best place I've found for a discussion regarding this amp, and the Lightning, is the Ampgarage. If you join you can search their archives and view schematics they've posted.

    This is the one that I have (note two pages and page 2 is slightly different than p1):
     

    Attached Files:

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  11. Mark the Moose

    Mark the Moose Tele-Meister

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    Thanks. I think in this case, I don’t care much about authenticity as long as it works well. A few deviations don’t bother me much.
     
  12. JuneauMike

    JuneauMike Friend of Leo's

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    ah yes, well, therein lies the controversy. Check out Ampgarage for some pretty good discussion about the Spitfire and filtering and plate voltage, etc. (I think I've seen where both of these iterations have been built and had happy customers).

    I did my own schematic with a one-tube reverb but have not built it.
     
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  13. dan40

    dan40 Tele-Afflicted Silver Supporter

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    There really are not enough preamp stages in these smaller tweed circuits to be able to effectively use a MV and get more dirt from the preamp. Most of these rely on the power amp's saturation to get a great OD tone. A nice attenuator may do you well for some early morning playing at quieter volumes though.
     
  14. kingofdogs1950

    kingofdogs1950 Tele-Holic

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    Another Mojotone 5f11 owner. (Built by Mojotone.)
    I've considered adding the bias pot, but the amp works great, and well, I'm lazy.
    I can't see much advantage to a MV.
    I did try a few different speakers. My amp came with both 10" and 12" baffles. It came with a Fat Jimmy 1025c and a Weber silver bell 12". The FJ is great and works wonderfully well for low volume home playing. It is a low efficiency speaker, although I have never seen specs on it. The other speakers, especially the 12s, are a lot louder.
    The Weber was not bad. I also tried an Emi RWB 12" and 1028k 10". Both were also not bad but I really like the FJ.
    I installed a full set of NOS tubes. Quieter and very smooth. V1 made the most difference.

    Mark
     
  15. jsnwhite619

    jsnwhite619 Friend of Leo's

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    What's your current B+? If you can still find a Hammond 290CAX PT, it offers 275v and 315v taps. If you have the Mojotone PT at 350v, it's probably a lot cleaner and louder than what the 275v tap can offer. I love the lower voltage tone, but the tremolo works better at 370v B+ and higher in my experience. Hammond's revised 290AX has a 275v & 325v tap and I know it's available, 100mA. I would replace the Mojo PT for that and use the lower voltage tap instead of spending money on the OT if you want earlier breakup. 275v secondary let's you bias it down to 300v range or lower, definitely will knock some power off if you are looking at 400v range right now.

    Absolutely add the bias pot, too easy not to.

    Tighter and better bass, at minimum try increasing the last filter cap for the preamp node to 22uf or more - I like F&T's. 22uf across all 3 would take that even further. More bass also usually means dirtier sound IME. Maybe not great for studio work if it farts out, but for playing at home, I think it helps saturate the OT a little quicker with more bass in there.

    I increased the NFB resistor on mine to 68k and it lowered the headroom a little bit.

    I have Hammond's 15 watt 8k Tweed Deluxe OT on mine, and their 22 watt 6.6k Deluxe Reverb on a Harvard. Definitely stick with an 8k OT for lower headroom and earlier breakup. I wouldn't "upgrade" it unless it was for a smaller transformer if quieter & dirtier is the goal.

    What speaker are you using?
     
  16. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Here's two clips I did of mine. The lower voltage was biased for best cleans, and the higher voltage was hotter for lowest headroom. I love the thick clean tone at the low 300v range. It does drive better at 370-375v B+, but it is louder and pushing more power. It's just tough to crank a 2x 6v6 tube amp and not get loud.
    With a Cannabis Rex speaker

    Clean


    Dirty.
     
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  17. jhundt

    jhundt Doctor of Teleocity

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    I spoke a bit too soon. The amp I made is closer to a Lightning. Essentially it is an AC-30 Top Boost preamp without the 'normal' channel, into an AC-15 power amp. Since I didn't include the 'normal' input, I had 1/2 of a 12ax7 left over. I wired it in parallel to the first stage, which is a Matchless trick - that's why I mentioned the Spitfire (erroneously).

    After several years I decided to rebuild the amp. Since the parallel-tube setup didn't seem to offer anything - I could never hear any change or improvement - I used the extra half for a generic gain-stage. I added an input jack and a switching jack so that the amp can be used with or without the extra boost stage.

    Sorry, at the moment I can't seem to locate my schematic. But it was all pretty standard; I think I used Weber's AC-30 kit schematic because it was easy to read; and I scribbled my changes on it.
     
  18. JuneauMike

    JuneauMike Friend of Leo's

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    That amp behaves beautifully with a 10 inch speaker (alnico, please), which is what it was designed to push. I've tried 10" and 12." The 10" is perfect for low volume.
     
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