5f1 mod for more gain + treble

Discussion in 'Glowing Bottle Tube Amp Forum' started by gobi_grey, Dec 10, 2019.

  1. gobi_grey

    gobi_grey Tele-Holic

    Posts:
    995
    Joined:
    Jun 7, 2011
    Location:
    clinton, ia
    I know it's been talked about many, many times but if someone could explain in easy to understand terms so I can try and do the mod myself. I would like to get more gain and brighten it up a bit. Much thanks in advance!
     
  2. jhundt

    jhundt Doctor of Teleocity

    Age:
    65
    Posts:
    11,789
    Joined:
    Mar 23, 2003
    Location:
    Netherlands
    sorry, we're not allowed to talk about that anymore.
     
    caspersvapors, D'tar and Rufus like this.
  3. Rufus

    Rufus Tele-Afflicted

    Posts:
    1,437
    Joined:
    Apr 13, 2004
    Location:
    NW Atlanta
    Hmmm...I was wondering how to get a little more clean headroom on mine!
    Playing thru a 10' or 12" speaker would help with my desires...

    One of the local tube amp gurus should be chiming in soon...good luck!
     
  4. cobaltu

    cobaltu Tele-Meister

    Posts:
    135
    Joined:
    Feb 19, 2010
    Location:
    New York, NY
    First off: you would need some soldering ability. You would also need to know were the cathode resistor is in a Champ.

    There are probably several ways you could do this; the easiest one would be to wire a cathode bypass cap, in parallel, with the first preamp tube cathode resistor. This resistor is the one that is 1500 ohms on the FAR right of the board looking at the chassis from the back (tubes closest to you). Its band markings would be brown, green, black, brown, with some tolerance marking band (probably either silver or gold).

    Any cap from 3.3 - 0.68uF would work. The larger the cap, the more lows are retained in the boost. 1uF might be a good starting point. The voltage on the cathode of a preamp tube is very low so a 25V cap will easily suffice.

    EDIT: if you are uncomfortable with this. TAKE IT TO A TECH.
     
  5. dan40

    dan40 Tele-Afflicted

    Posts:
    1,462
    Joined:
    Aug 19, 2015
    Location:
    Richmond Va
    Another option would be a switch to disconnect the nfb circuit. This would also require some soldering skills and you will be working inside the chassis where you may be exposed to high voltage. A tech could do this in under an hour if you are unsure of the process.
     
    jsnwhite619 likes this.
  6. cobaltu

    cobaltu Tele-Meister

    Posts:
    135
    Joined:
    Feb 19, 2010
    Location:
    New York, NY
    This is another option but it wouldn't create a treble boost. Unless, you also created a presence control which bypasses high frequencies from the negative feedback loop. but this is a lot of legwork for someone who might be new to soldering.
     
  7. hdvades

    hdvades Tele-Holic Silver Supporter

    Age:
    59
    Posts:
    591
    Joined:
    Mar 6, 2016
    Location:
    Hudson Valley, NY
    Turn the amp up to 5 or more for gain and a little bit less for brightness and get the treble out of the guitar maybe.
     
  8. dan40

    dan40 Tele-Afflicted

    Posts:
    1,462
    Joined:
    Aug 19, 2015
    Location:
    Richmond Va
    I agree that cutting the nfb will not boost treble frequencies the way the bypass cap would, but in every amp that I have removed nfb from, the sound did seem a touch brighter without the nfb limiting the bandwidth.
     
    jsnwhite619 likes this.
  9. gobi_grey

    gobi_grey Tele-Holic

    Posts:
    995
    Joined:
    Jun 7, 2011
    Location:
    clinton, ia
    At 5 mine is quiet, clean and dull. When you turn the knob to switch it on, it doesn't turn on until about 2, no sound at all until about 3 1/2 on the dial.
    Don't really start getting gain until about 8 on the dial.
     
  10. hdvades

    hdvades Tele-Holic Silver Supporter

    Age:
    59
    Posts:
    591
    Joined:
    Mar 6, 2016
    Location:
    Hudson Valley, NY
    I hear ya. That's a 5f1. Turn on and increase volume dial until you have sound and turn knob a little more clockwise. The one I have has no speaker output below 4.
     
  11. Ess Eff

    Ess Eff Tele-Meister

    Posts:
    440
    Joined:
    Nov 6, 2018
    Location:
    Australia
    NFB on a 5F1, where??

    Most ppl find the 5F1 to be too gainy. You sure everything is ok with it? It can be pretty warm tho.
    .
     
    Last edited: Dec 10, 2019
  12. dan40

    dan40 Tele-Afflicted

    Posts:
    1,462
    Joined:
    Aug 19, 2015
    Location:
    Richmond Va
  13. peteb

    peteb Friend of Leo's

    Posts:
    4,200
    Joined:
    Apr 25, 2003
    Location:
    Cascadia
    I agree with the other suggestions.

    Cathode bypass caps, remove NFB for more gain but not more treble.


    Solid state rectifier?


    EQ pedal plus a booster pedal?

    Treble booster pedal?
     
  14. Rufus

    Rufus Tele-Afflicted

    Posts:
    1,437
    Joined:
    Apr 13, 2004
    Location:
    NW Atlanta
    Wow...my vintage late 50s tweed Champ gets sound as soon as the dial is turned on and is screaming by 5 on the volume.
    Are you guys sure yours don't need to be serviced?
     
    wrathfuldeity likes this.
  15. Linkjr

    Linkjr Tele-Meister

    Age:
    49
    Posts:
    116
    Joined:
    Aug 16, 2017
    Location:
    Uk
    Does your vintage champ knob go all the way to 12 as well?
     
  16. VintageSG

    VintageSG Friend of Leo's Ad Free Member

    Posts:
    3,426
    Joined:
    Mar 31, 2016
    Location:
    Yorkshire
    Try a 470nF bypass cap on V1a and a 22uF on V1b and switch out the NFB. That's about all you can do before you need an EQ pedal/boost pedal.
     
    dan40 likes this.
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.


  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.