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Thread: Blackvibe - No Reverb, No Tremolo, 1 Channel AB763 Blackface

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    Blackvibe - No Reverb, No Tremolo, 1 Channel AB763 Blackface

    The 1963 Fender AB763 blackface Vibroverb is my favorite amp of all time. It will be forever linked to Stevie Ray Vaughan's amazing tone but building a blackface Vibroverb is a daunting task, even for an experienced amp builder. I designed the RR763 Blackvibe amp for builders who don't want to deal with the complexity of the AB763 circuit's reverb, tremolo and dual channels but still want its authentic Normal channel tone. Throw a Strymon Flint reverb & tremolo pedal in front of the Blackvibe and you have a Vibroverb Vibrato channel too.

    Removing the reverb, tremolo and Vibrato Channel drops the preamp tube count to only two but the tone stays 100% Normal Channel Vibroverb. The rest of the amp stays true to the Vibroverb. This amp uses authentic Vibroverb power and output transformers and choke so voltage levels and power output are all blackface Vibroverb.

    Note: All of my amp designs, Blackvibe, JCM800 Micro, Bassman Micro, RobRob Deluxe, etc., are released under the Open Source Hardware Association license. You may build, modify and sell my designs without limit. All I ask is that for amps you sell you include, "Design by RobRobinette.com" on your webpage and advertising.

    Click image for larger version. 

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    It's very much a single channel Vibroverb with standard 6L6GC power tubes.
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    Blackvibe vs True Blackface Tone
    Johannes Specht from Vienna, Austria built a Blackvibe 6V6 and compared it to his original 1966 blackface Deluxe Reverb. For a direct comparison between the two, Johannes recorded a Strat into a TC Electronic Looper to get exactly the same signal into both amps. He also used the same cab with a Weber 12F150 for both amps and recorded mostly dry with just a bit of dirt and reverb/delay in post production.

    Here's his 66 Deluxe Reverb Normal channel mp3

    Here's the Blackvibe mp3

    You be the judge of the authenticity of the Blackvibe tone.

    Click image for larger version. 

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    There is also a 6V6 and micro (12AU7 true push-pull) Blackvibe available.

    Details of the amp are here: https://robrobinette.com/RR763_BLACKVIBE.htm

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    Sweet amp, thanks!

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    The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

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    Hi Rob, so the power trans. and output trans are the same as vibroverb spec?

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    The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

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    Yes, I suggest the Classictone spec for the real Vibroverb's PT, OT and choke. Of course the 6V6 and micro versions use different iron.

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    Supporting Member loudthud's Avatar
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    I'm wondering about the 100K Mid pot. Was that a Stevie Ray thing ? Is it documented anywhere ?

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    WARNING! Musical Instrument amplifiers contain lethal voltages and can retain them even when unplugged. Refer service to qualified personnel.
    REMEMBER: Everybody knows that smokin' ain't allowed in school !

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    No, the Vibroverb has no mid pot. I added one since the removal of the vibrato, tremolo and Vibrato channel left extra chassis pot holes. The 6.8k mid resistor is still there so with the Mid control turned full down you get the standard tone but turning up the control adds mids and gain and allows us to get into tweed territory.

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    Why do you cut the negative side of the voltage supply coming from the transformer?

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    In this forum everyone is entitled to my opinion.

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    With HT windings much over 600Vac (unless used as series pairs), 1N4007 are underrated for use as backup diodes for the rectifier tube. It would be a dreadful shame for failure of the rectifier tube to be followed by failure of its backup silicon diodes

    Need to factor in highest mains voltage (eg x 1.08) and unloaded HT (eg x 1.1), then the rms-to-peak ratio x 1.414. So that works out to ~1.68 x the (loaded) HT winding voltage; so rating should be >=1k2V for your PT.
    http://www.valvewizard.co.uk/bridge.html

    Fusing for the HT would be extremely beneficial, especially as the screen grid resistor rating has been significantly increased. When used in this application (regular 6L6 type tube guitar amps) I've never come across 1 watt 470 ohm resistors burning out, other than as collateral damage from a tube short.

    To facilitate less hazardous power tube current measurement, why not include 1 ohm cathode resistors for the power tubes?

    It's great that the layout drawing show a dedicated safety ground chassis connection and a DP mains switch. And that the HT CT is wired directly to the reservoir -ve terminal.

    The schematic shows a SP mains switch.

    Also its treble pot is marked 'L', presumably linear, whereas the layout's is shown as log.

    Why the recommendation for a AB763 Pro chassis to be used; isn't it overly long?

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    Last edited by pdf64; 08-16-2019 at 02:22 PM.

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