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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

5F11 - bypass cap on V2?

Discussion in 'Shock Brother's DIY Amps' started by jsnwhite619, Nov 30, 2017.

  1. jsnwhite619

    jsnwhite619 Tele-Afflicted Ad Free Member

    Sep 10, 2013
    Georgia
    Could I add a bypass cap here on my Vibrolux for a gain boost? My first though is that the NFB will kill it, but if I put the NFB on a switch with a cap on there, would it be ON - w/NFB and the cap essentially not working OFF - no NFB, and extra gain from the bypass cap?
     

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  2. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    Take a look at the BF Princeton Amps, which are the descendants of that 5F11. You will see that they did indeed install a bypass cap there....but with a change in the NFB resistance and the bias resistor for that cathode.
     

  3. jsnwhite619

    jsnwhite619 Tele-Afflicted Ad Free Member

    Sep 10, 2013
    Georgia
    Thanks @Wally That's actually the NFB setup I used on my 5e3 and it worked out well for keeping the gain up. I just realized I was thinking about it backwards -- looking at Rob's 5e3 NFB info, the bypass cap cancelled the NFB, and I was thinking the other way around. If the cap was there, it would cancel the NFB, I guess. Hence using the Princeton style with the extra 47 ohm resistor to separate things. And the much lower value NFB resistor.
     

  4. Wally

    Wally Telefied Ad Free Member

    Mar 17, 2003
    Lubbock, TX
    There is an equation for that NFB factor using the ‘top’ resistance and the tail resistance. In your 5F11, that 1500ohm resistor doubles to set the bias for that triode and as the tail resistance. In the BF amp, the cathod bypass is not in that loop and the tail resistor for the NFB loop is the 47 ohm. Aiken has a good article I; his tech pages and gives that formula.
     
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  5. keithb7

    keithb7 Friend of Leo's

    Age:
    46
    Jan 9, 2010
    Western Canada
    I will chirp in and tell you about a cathode cap I added to second stage V1 in a 6G2. It works. Experiment with values. What sounds great with a single coil Strat, reminds me of Gallagher. “Mushy watermelons squeezed in a vice” when played thru humbuckers.

    2 cathode caps and a 3 position switch might be cool. But then yer tweed starts to represent a Mesa Atlantic amp. Which has what? 50 or 100 switchable options.

    With the extra cathode gain, switching NFB off and on had little to no effect.
     
    Last edited: Dec 1, 2017
    jsnwhite619 likes this.

  6. jsnwhite619

    jsnwhite619 Tele-Afflicted Ad Free Member

    Sep 10, 2013
    Georgia
    Thanks for chiming in. It was actually your mod that got me thinking because we are essentially talking about the same amp. The "too much of a good thing" with the humbuckers is good to know in advance.
     
    keithb7 likes this.

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