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5881 in a 5f2a

Discussion in 'Shock Brother's DIY Amps' started by jsnwhite619, Jul 11, 2020.

  1. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Thanks! I just listened and it sounds WAY muddier on my phone than it does in person or even on my desktop computer. So, there's that.
     
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  2. D'tar

    D'tar Friend of Leo's

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    Yeah but it still sounds good! Perhaps our phone speakers are out of phase with your amp!;)
     
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  3. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Well, after playing with it some more with the C-Rex, I think I am going to cut some bass on it. Lesson learned - don't try to tune an amp if it's not already matched with the cabinet and speaker it's going in.
     
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  4. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Swapped the .1uf coupling cap for a .047uf. Can't crank it up tonight, but I don't think I lost anything bill miss.

    Low level clean, volume at 3 on the low input.

     
  5. cobaltu

    cobaltu Tele-Meister

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    I'm not sure it's bass you're hearing, but low mids. 5F2a's have a lot of those in their tone stack, and the Cannabis-Rex has a lot too. Are your tone stack values stock?
     
  6. scurkro

    scurkro TDPRI Member

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    Hi @jsnwhite619 – awesome sounding amp, love it!! This is a little off-topic, but I just wondered what type of switch you used for the NFB? Is it an SPDT mini toggle?
     
  7. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Thanks! Yes, the little red-base mini switch. I actually ended up leaving a fixed NFB value, and I moved the switch to the 2nd bypass cap for a "fat boost". So, one way gives closer to a stock Champ sound, the other adds a 25uf bypass cap on the back end of the preamp.

    I loaned it to a friend who wanted to try it out. I ended up sticking with the 2.7k bias resistor. I am going to attribute it to that, but he said it's the best amp of any he's ever owned for overdrive pedals. I didn't try one with it - he doesn't want to give it back yet ;-) -- but I went back and read again on Rob's site about using the 2.7k bias resistor and he mentions that it may take a pedal boost to really bring out the harmonic benefit of that setup. So, maybe that's the secret? But, apparently, he said it's done great with every OD he's put in front of it. He sent me a couple audio clips he recorded with his cell. Not the best quality, but I've got to say it sounded like a Marshall stack in the room.
     
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  8. James Knox

    James Knox Tele-Holic Silver Supporter

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    That is a beautiful cab! Is it a Deluxe 16” X 20”? Depth? Taper?
     
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  9. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Yep. Around 10" base and 4-5° taper.
     
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  10. James Knox

    James Knox Tele-Holic Silver Supporter

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    Your Bud who is gigging your 5881 Prince is breaking in the Cannibus for you, lol. Never played through one. How long do they take to break in?
     
  11. D'tar

    D'tar Friend of Leo's

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    420 hours!!!
     
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  12. James Knox

    James Knox Tele-Holic Silver Supporter

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    Ouch!
     
  13. James Knox

    James Knox Tele-Holic Silver Supporter

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    Does having the last Filter Cap a 22uf (over the normal 8uf) take away from the tactile response?

    If you can wrangle the amp back from your Bud, will we still get a recap? I think I’ve followed along and made some notes, but you might have some final tweeks and thoughts.
     
  14. jsnwhite619

    jsnwhite619 Friend of Leo's

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    Well, I think this one already ended up in a new home - he made me an offer I couldn't refuse!

    He sent me this cell clip running clean through a compressor then hitting a DS-1.

     
  15. James Knox

    James Knox Tele-Holic Silver Supporter

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    @jsnwhite619 for those who have watched this build are inspired to follow in your footsteps (YES), would it be possible for a Final recap?

    I’ve made some notes But might have missed one of the rolling changes. Or maybe some final tweaks you might have done.
     
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  16. Timmay

    Timmay Tele-Meister

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    I'll second this!!! I'm new to this. I purchased a 5f2a copy on ebay with suitable transformers with the intent of rebiasing it for 5881 or 6l6. Came here to gain some education on the matter, and right there on the first page was this thread. I think I know what I need parts wise, but a final recap would be great.
     
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  17. James Knox

    James Knox Tele-Holic Silver Supporter

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    @jsnwhite619

    I am currently following in your footsteps with a “Big Bottle” 5F2A! Populating the circuit board today and just wondering if you had any final changes or thoughts on your build. You had mentioned a final recap?

    Thanks for the inspiration and fun build!

    Peace,

    James
     
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  18. jsnwhite619

    jsnwhite619 Friend of Leo's

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    @James Knox I honestly don't remember beyond what I listed in here. I was going to do a final runthrough when I got it back, and now it ain't coming back! :lol:

    Other than increasing the resistor ratings for the 5881 - power resistors and 10W bias resistor - it really was probably 90% stock. 15W OT from ClassicTone with the 5k winding. 290AX PT with a 3A winding to handle a 5u4. Heavier filter section. There was so much trial & error and A/B testing I would probably have to borrow it back from him to build another one like it. The rest is basically playing with bypass caps and 12ax7 vs 12ay7 V1. I like more circuit gain with a 12ay7 more than a calmer amp with a 12ax7, but I can't actually describe why - just a personal preference.

    No matter what, a juiced up 6v6 Tweed Princeton with a big cabinet and high efficiency 12" speaker is loud enough for me to gig with if I'm the only electric guitar player. The 5881 version with a 5e3 cab and Cannabis Rex was way louder than I would gig in the same situation with when it was beyond 2/3 volume. As long as you account for the power requirements of using the 5881, you should still end up with a rocking amp that will basically keep up with a 5e3 with the right speaker & cabinet.

    My buddy said he usually keeps the volume on 3 and uses an overdrive pedal at home...sounds great at 6 but it's just too loud! Point is that it's freaking louder than you think it will be for a "little Tweed Princeton". So, plan accordingly... ;)
     
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  19. James Knox

    James Knox Tele-Holic Silver Supporter

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    Thanks for the reply!

    I’m enjoying the build (my first 5F2A) and plan on comparing it to my 5E3, keeping my favorite. I tend to lean toward SE Amps over PP.
     
  20. chas.wahl

    chas.wahl Tele-Meister

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    Did you accidentally reverse 12AY7 and 12AX7 above, or did you really mean 12AY7 has "more circuit gain" and 12AX7 results in a "calmer amp"?
     
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