Like an AB763 reverb-amp with octal tubes because bigger!

Discussion in 'Shock Brother's DIY Amps' started by Snfoilhat, Aug 18, 2019.

  1. Snfoilhat

    Snfoilhat Tele-Afflicted

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    Standing on the shoulders of giants https://robrobinette.com/RR763_BLACKVIBE.htm and using up a cache of octal tubes from a couple '50s reel-to-reels.

    The proper Blackvibe is based on the AB763 Normal channel, but at the bottom of the page is some discussion of building the AB763 Vibrato channel to add reverb but deleting the tremolo. That was my primary inspiration for this.

    I've got a chassis, a set of transformers, a set of tubes, a spare combo cab. I'm missing most of the caps, pots, and some hardware odds and ends. Whether the parts order goes out in September or in December depends on how the beginning of the semester goes. Plenty of time to gather some feedback.

    My chassis has one slide switch opening where you'd find a Bright switch. I don't want a bright cap, so I'm deciding between a switchable mid frequency shift or a Rivera-era mid boost or a Vox-style bass cut, each of which I've used in other amps. Or maybe something else? Headroom? Bias?

    My 6SL7 gain stages will each be lower gain than 12AX7 stages, and my 6SN7 long-tailed pair PI should have less gain than a 12AT7 LTP PI, so I anticipate playing it w/ the volume control set higher than a proper AB763 Deluxe Reverb at similar room volumes. I'm interested to learn if this brings more preamp flavor into the sound or less. More touch-sensitivity or less.

    Reverb_Amp_II_18AUG2019.png
    Might need a choke.

    Screenshot from 2019-08-18 11-08-12.png
    Tone stack calculator with the mids resistor set around 6.8k and using various caps.

    White is the Super Reverb, yellow is the stock configuration for many other Fenders, red is the mid-shift setting shown on the schematic above, blue is the mid-boost from Rivera-era amps where a 2700 pF cap is paralleled with the 250 pF treble cap. I don't remember liking this sound, but included it for completeness' sake. Gotta use that switch hole for something!
     
    Last edited: Aug 18, 2019
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  2. Snfoilhat

    Snfoilhat Tele-Afflicted

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    Tangent

    I found some cool stuff on the curbside. 1) An old low voltage DC power supply with cool modules that wrap a small circuit board with rectifier, smoothing caps, other components, and a power transformer all in a metal case with socket pin connecters. The modules mate to sockets in the small aluminum chassis that houses the user interface parts.
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    I have a modern version of this device that a friend rescued from her old laboratory, sitting unused on a shelf. 0-30VDC, 0-1A. This one at least I may fit a small, 2-tube amp in this chassis and all the holes already punched, someday down the road. Until then there's a shelf for it...

    2) a neighbor curbed a nice 10 foot length of 1x12" pine and 20 feet of a little chewed-up looking 1x10" pine that may have served as shelving or some other jury-rigged home furnishing. So there are materials to build another extra-deep combo cab plus who knows what else. Cheers
     
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  3. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    mmmmmmmmmmmmm octals :D
     
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