New Build: 5F11 Vibrolux

Discussion in 'Amp Central Station' started by Bob Arbogast, May 9, 2019.

  1. Bob Arbogast

    Bob Arbogast Tele-Afflicted

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    I just finished this amp the other day. I used a Mojotone kit and made just a few substitutions. I also added a couple of components to the bias circuit to reset the bias adjustment range and to quiet the tremolo circuit.

    I intend to use this amp for gigs at very small venues. It sounds great, though I will soon swap in a Copperhead speaker. I'm looking for more low-mids and less highs.

    I saw the color scheme on the Gear Page (user: ripple). It's VOX fawn tolex and Bluesbreaker grill cloth.


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  2. Blue Monster 65

    Blue Monster 65 TDPRI Member

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    Nice work! I’d like to hear it.
     
  3. theprofessor

    theprofessor Friend of Leo's

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    Um... WOW! That's off the hook! Congratulations on a very fine new build. If it sounds half as good as it looks, you're in business!
     
    King Fan likes this.
  4. Mark the Moose

    Mark the Moose Tele-Meister

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    I dig the fawn tolex.
     
  5. dannyh

    dannyh Tele-Afflicted

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    Looks great, bet it sounds great too..,congrats!
     
  6. AlbertaGriff

    AlbertaGriff Tele-Holic

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    Awesome, looks fantastic inside and out. I'd like to do a mojotone 5f11 kit as well some day.
     
  7. dragonfly66

    dragonfly66 Friend of Leo's Silver Supporter

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    Nice, nice, nice!!
     
  8. gridlock

    gridlock Friend of Leo's

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    Excellent job and a beautiful amp.
    Congrats.
     
  9. jhundt

    jhundt Doctor of Teleocity

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    Beautiful! I built one of those a while ago, and I love it.

    Can you elaborate a bit on what you altered in the bias circuit?
     
  10. Uncle Daddy

    Uncle Daddy Tele-Holic

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    Nicely done. Do you get much trem whump creeping through?
     
  11. Bob Arbogast

    Bob Arbogast Tele-Afflicted

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    Thanks, all!

    The way Mojo lays out the bias circuit, it has a very limited adjustment range. In fact with the stock values, the 6V6s were running too hot. So I experimented with the value of the first resistor in the bias string. I added a 33k to the stock 10k and that put the bias adjustment in the right range.

    Yes, there is some of that. It's not too noticeable when playing. I added a second 25uF/50V cap in parallel with the bias cap. It helped. Right now the workaround is to use the footswitch to turn off the trem oscillator.
     
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  12. AJBaker

    AJBaker Friend of Leo's

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    Nice!
     
  13. charlie chitlin

    charlie chitlin Doctor of Teleocity Silver Supporter

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    Very sanitary.
     
  14. jhundt

    jhundt Doctor of Teleocity

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    thanks for the info. One more question, if I may: What amount of bias do you use?
     
  15. kookaburra

    kookaburra Tele-Afflicted

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    Hi Bob, why a Copperhead instead of the Ragin' Cajun? I'm only familiar with the speakers from discussions regarding Allen amps.
     
  16. King Fan

    King Fan Friend of Leo's Ad Free Member

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    Agree, a beautiful build. Re trem thump, assuming the 5F11 trem array is quite close the 6G2's, I recall where our friend @theprofessor took a page from Jim Nickelson's LilDawg book using 47pf silver mica caps. I was so impressed I stole and marked up his photo:

    Professor 6G2 trem thump caps.jpg
     
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  17. schmee

    schmee Poster Extraordinaire

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    Love the look of that amp.
     
  18. Bob Arbogast

    Bob Arbogast Tele-Afflicted

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    Here are some numbers:

    Line voltage: 122Vac
    Plate voltage: 405Vdc
    Screen voltage: 408Vdc
    Cathode current: 21mA
    Screen current: ~1mA
    Bias voltage: -37Vdc

    Frequency response charts and my memory tell me that the Copperhead is not as bright as the RCajun. That's a key goal.

    Thanks for that. The trem thump is not so bad. What I do have is some low-level hum.

    I'm confident that the first part of the hum is magnetically coupled from the PT to the OT. The hum comes through the speaker even with no tubes installed. (I had the same issue years ago with RI JTM45 heads.)

    The second part of the hum seems to come from the bias or trem circuits. The hum decreases as the I turn up the Depth control.

    It's all quite minor. Not something you hear when you're playing. And certainly nothing you would hear in a live setting, even when you stop playing!
     
    kingofdogs1950 and kookaburra like this.
  19. Mike Eskimo

    Mike Eskimo Doctor of Teleocity Ad Free Member

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    Celestion vintage 10 (if you need a 10)

    Great speaker that I bet would work great in there.

    Nice choice on the tolex and grill
     
  20. kingofdogs1950

    kingofdogs1950 Tele-Holic

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    Nice looking amp.
    I have the same 5f11 built by Mojotone. Mine is unmodified.

    Mark
     
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