Getting MORE saturation from a Champ

Discussion in 'Amp Central Station' started by holio cornolio, Jul 8, 2021.

  1. Linkjr

    Linkjr Tele-Meister

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    Im not sure you going to get where you want to be altering the circuit anymore, what you need is to build in an attenuator, in my experience my simple attenuator has better results on my champ than a boutique transparent boost / overdrive pedal.
     
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  2. VintageSG

    VintageSG Friend of Leo's Silver Supporter

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    Attenuators are indeed very good. The Bugera PS1 is a clone of the Jet City Jettenuator, Thomann also produced a variant under their Harley Benton brand ( The model I have ) and it's something I won't be without now.
    How about running the output as a triode? The Special 6 schematic shows a simple way to do this. Power drops to around 60%-ish and the characteristics change a little, but more valve saturation and compression effects.
     

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  3. teleman1

    teleman1 Friend of Leo's

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    What size speaker are you using. 8" ? Remember smooth cone breaks up earlier than ribbed.
     
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  4. holio cornolio

    holio cornolio TDPRI Member

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    It's a Jensen p8r.
    I also cracked her open and measure plate voltages and bias. So, bearing in mind that this was in my home office which is in the garden powered on a spur from the house mains electricity, and voltage at the plug point is a bit less than 240v, there's only about 275volts at the 6v6. Bias seems to be 29ma which I think is about right for that voltage, but according to the spec, the transformer should be delivering aboboutu 330v to the plate. So, anyway, I'm thinking that lower plate voltage should actually give earlier breakup. No?
     
  5. 2L man

    2L man Tele-Holic

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    PS output voltage is very low for average OT impedance.

    This is the loadline for 8k OT impedance using values you posted.
     
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  6. holio cornolio

    holio cornolio TDPRI Member

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    Yeah I thought it was about 290 when I built the amp. Since then my home office has been professionally rewired, and the ringmain that I installed has been replaced with a spur (to meet some regs that I don't pretend to understand). Consequently I'm getting less mains voltage so that may be a factor, but I do think the OT was weak when i built the amp. Maybe I should pony up for a better one. Only thing is I don't really know what to specify so I'd be going back to cause to get an OT and I'd probably get the same type as replacement.
     
  7. 2L man

    2L man Tele-Holic

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    I have used Hammonds: 1750C and 1760C (257g) for one 6V6 and 125DSE (972g) for one EL34.

    I recently bought reasonably priced 10W Piemme SE OT (753g) from Italy and drive it using one 5881.

    My best sounding SE is VDV-2512-SEE (955g) Toroidal OT designed for HiFi and I came from Holland but it was expensive. It has very clear sound and tube distortion comes articulate but so far I have biased it to max 80mA although it can take 100mA.

    I have began building a SE for one KT88 and will use use two 125CSE which max bias is 60mA. For two OT parallel I will bias to about 115mA which should be enough workload for one KT88 using power transformer which outputs 250VAC. One 125CSE weights 700g so 1400g for an OT which can be biased to 120mA is not too bad weight.

    Best power/weight ratio would come using as many parallel 1750C or 1760C as needed. Possibly I must build one in the future :)

    Single ended OT datasheet should specify max bias current.
     
    Last edited: Jul 20, 2021
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  8. memorex

    memorex Friend of Leo's

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  9. holio cornolio

    holio cornolio TDPRI Member

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    This amp has no tone stack to lift . I built it without a tone control for max input gain.
     
  10. memorex

    memorex Friend of Leo's

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    The original Champ had a treble and bass control with a fixed mid that went to ground. If you put in a switch to lift the ground, the tone stack was effectively bypassed, and the amp suddenly picked up a lot of gain, and could saturate like crazy. But it also got a lot louder, and could easily blow out the stock speaker. Back in the day, Radio Shack used to sell an 8" guitar speaker. It was painted orange and I don't know who made it, but it was perfect for a Champ replacement. I used to put that speaker in everyone's Champ that blew out the original after the tone stack mod.
     
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  11. holio cornolio

    holio cornolio TDPRI Member

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    I don't think the champ got a tone stack until the 60s. The first versions, 5b1 from the early 50s and onwards just had a single volume control, hence they're louder and overdrive easier than the black and silver face variants. I wasn't there in the 50s,and I've been wrong because I believed the internet before, but I've definitely played through an orig 50s tweed champ and it was exactly as it left the factory and had no tone stack. It was beautiful.
     
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  12. Linkjr

    Linkjr Tele-Meister

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    I prefer the orig tweed champ sound over any blackface champ
    Even with blackface modded tone stack lift the tweed got the snarl at high vol but it is sweet as a baby lower down and sounds like the old records
     
  13. Killing Floor

    Killing Floor Poster Extraordinaire Silver Supporter

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    Preamp? I have several I enjoy that use 1,2 or 3 12AX7 tubes. You can deliver real tube break because they are real tubes. So you’re not having to dime your amp to make it sound like a dimed stack.
    Just a thought.
     
  14. chris m.

    chris m. Poster Extraordinaire

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    I don't know about amp mods. But I put a Red Fang alnico speaker in my MMB amp and boy, what a difference it made in terms of getting a woolier sound. I doubt they come in 8" but I second the recommendation for a speaker change. Huge impact on tone!
     
  15. David Barnett

    David Barnett Doctor of Teleocity Ad Free Member

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    Maybe try converting the input to grid leak bias?
     
  16. Lynxtrap

    Lynxtrap Tele-Afflicted

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    What I would do to squeeze a little more juice out of that circuit with some nips and tucks:
    - Lower the input grid resistors to 33 or 22K.
    - change the 100K plate resistors to 220K for both preamp tubes.
    - lower the cathode bypass cap on the first stage.
    - install a cathode bypass cap on the second stage.
    - remove the NFB
    - try a 330K or 470K grid leak resistor on the power tube.
    - replace the choke with a high watt resistor (saggier response similar to lowering B+).
     
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