Conversion: Spectras (Vibrochamp, 6G2)

Discussion in 'Shock Brother's DIY Amps' started by Drew617, Sep 2, 2021.

  1. Drew617

    Drew617 Tele-Holic Silver Supporter

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    Here's a pair of JMF Spectra amps, a 110 and an 80A. I picked these up cheap because the cabs (MDF, alas) and chassis are substantial and in useful configurations, and because I enjoy how very 1982 they look.

    At the moment, these look to me like some flavor of Vibrochamp, and a brown Princeton. Or a Vibrochamp and a Blackvibe 6L6, jammed into that cabinet early Boogie-style. Or a Vibrochamp and a Harvard. Hmm.

    These projects are likely to be kind of a slow burn, although we are quarantining for at least the next week or two.

    Kinda too bad as these are rather nice clean amps as-is, the little 80A especially. Not that too bad, though.

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  2. J. Bonkosky

    J. Bonkosky Tele-Holic Gold Supporter

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    I would just rock those two as is.
     
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  3. Drew617

    Drew617 Tele-Holic Silver Supporter

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    Nah, gutted both already anyway and am halfway through cleaning. Gain tones are as bad as suspected, and the big one's full of spiders anyway.

    I'll hang on to the 10" speaker though. It's a Pyle with a very soft suspension, but a JBL-type cone instead of the ribbed-seamed paper I expected.
     
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  4. cometazzi

    cometazzi Tele-Afflicted Silver Supporter

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    A guy I know just recently picked up a Spectra as a basket case and got it going. I want to say a 125? In any event he's going to use it for Pedal Steel Guitar. The OD channel got smoothed out with some caps in parallel with the diodes (which were right on the pot) but otherwise the cleans are great.

    I agree they look toadilly cool too!
     
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  5. Drew617

    Drew617 Tele-Holic Silver Supporter

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    But did it have spiders?! It’s a science fact that spiders increase amp mojo 100%.

    I’m going to end up ruining the cosmetics at least a little. Those aluminum trim bits on the baffle don’t come off without tearing the graphics off first.
     
  6. cometazzi

    cometazzi Tele-Afflicted Silver Supporter

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    Booo.... try your best not to deface it.

    I don't believe there were spiders, no. Lots of dust, but no spiders. Maybe he should have asked for a discount!
     
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  7. Drew617

    Drew617 Tele-Holic Silver Supporter

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    Seriously. They’re probably genuine 1980s spiders, too. Back when spider eggs had soul, and I was a grade schooler with a full head of hair. I wouldn’t pay a dime for garbage modern reproduction spiders. They’re made overseas now by Soviet mime troupes. Sure they hold the electrons in just as well, but anyone who knows will tell you it just ain’t the same.

    The adhesive graphic strips are mangled, sadly, and I’ll have to replace the grille cloth either way. Rather, I insist on it because what’s there is gross. The aluminum strips are fine, and have to be an off the shelf part… it’s the same stuff, a strip with a channel in it, that holds name tags on doors in municipal offices.
     
    Last edited: Sep 2, 2021
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  8. cometazzi

    cometazzi Tele-Afflicted Silver Supporter

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    1980s spiders are incredibly rare now, true. I may or may not have entertained one or more Soviet Spiders. They showed me how to make some Chebureki, Pelmeni and refreshing Kvass. They didn't really make my music sound any better, but my culinary skills are much more cheeki-breeki, even if everything now has mayonez...


    When it comes to 80s hair, I was still a blonde grade and middle-schooler, and near the end started to grow it down to the middle of my back. At least I had rad hair when I could! Now I have to wear a hat to avoid dome-scorching by the Yellow Face.


    Nonetheless, 'tis unfortunate that the aesthetics must be mangled for progress. You gotta break a few eggs to fake a ham sandwich, as Babushka would say.
     
    Last edited: Sep 2, 2021
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  9. Drew617

    Drew617 Tele-Holic Silver Supporter

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    That makes everything better, including the music. I come from a place where every third Browns, Steelers, or Knights of Columbus bar served halusky on Friday night. That was usually just egg noodles, but the world's nicer for it anyway.

    One time I was directed to a fairly precious restaurant in Montreal to have their borscht. I'm a quarter Romanian by the way, the rest Swiss and English, and don't identify as anything but "white person." I can't tell you why my friends believe I want Polish and Ukrainian foods, but they do. I suppose because I eat them. The foods, not my friends. Anyway: It struck me that the usual relationships between substance and pretense and beets were being violated.

    We're probably similarly unyoung and unhairful. But there's still space and energy for unpretentious and futile pursuits, like trying to maintain the integrity of a cheap old object. Sure the result won't be valuable, but that's the best part - you're left to assess its actual value.

    It was a lot easier to keep stock cosmetics when I gutted and built an amp inside a more recent Peavey. All the plastic bits get real brittle after a while, and the chipboard turns to granola. I thought about doing a bigger one but figured the Bandit people might yell at me for ruining a perfectly good Best Amp Ever. :D

    I already have to lose those awesome knobs with the Eurostile numbers because I can't find appropriately-shafted 3M reverse audio pots.

    A couple projects down the line, I'm going to build a GA-5 inside an absolutely roached Harmony H-191. Not an expensive object, but more historically valuable than that stuff. I probably will go out of my way to keep that one looking right, at least from the front.
     
    Last edited: Sep 3, 2021
  10. Drew617

    Drew617 Tele-Holic Silver Supporter

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    OK, well make these a more or less faithful 6G2 and Vibro Champ. I'll use Fender-style eyelet boards for both. The 6G2 will use a Weber Champ PT (tube recto, target B+ ~350 VDC) and a MPS OT12PP OT. In the VC, I'll use a $28 Weber WRVBPT (diode recto, target B+ ~355) and their WSE15 OT.

    Waiting on small parts from tubedepot and a couple more WRVBTs from Weber.

    For now, quick and dirty layout/drill plan on the underside of what will be the 6G2 chassis:

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    De-stapled, -grilleclothed, -spidered and -spored both baffles, applied fresh rustoleum, installed new cloth and speakers. Using smooth cone, ceramic Weber Signatures in each.

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  11. Drew617

    Drew617 Tele-Holic Silver Supporter

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    Chassis drilled, punched, and rustoleum'd. Cabs scrubbed, armor all'd, and hardware reinstalled.

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  12. Drew617

    Drew617 Tele-Holic Silver Supporter

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    Assembling chassis, some hardware and power supply boards.

    Using Fender-style fiberboard here. Not my favorite but easy to get with minimal effort, and a Hoffman board would've been too wide for the VC chassis. Those are populated but I'm waiting on a few odd value resistors that I didn't have in stock.

    Forgetting about stock cosmetics. I test fit these and realized the off-white chassis made these look a bit like a 60s Gibson and I liked the effect. I'll deal with faceplates later, or not.

    I can't make the monster WSE15 OT fit, so will use their Champ OT instead, still a bit bigger than a real Champ OT.

    I've got a pair of WSE15s now that are not allocated to any project in particular. Maybe time for a hifi amp.

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  13. Drew617

    Drew617 Tele-Holic Silver Supporter

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    Haven't taken a complete voltage chart yet, but I've got a healthy Princeton that sounds about like a Princeton. After I remembered to ground the 6V6 cathodes, anyway.

    I took advantage of much of @King Fan's work and documentation here - thanks. :)

    B+ is ~375, I forgot this is the Weber 300-0-300 PT rather than the Hammond 275-0-275. If it ends up feeling too stiff I'll address that with (ugh) a dropping resistor. Feels just fine during a quick shakedown, however. The speaker's a Weber Sig10 (smooth cone) which I figured may fit the 6G2 character nicely. I have a 10F150T on hand which I figured may counter the 6G2's basic character, but I think that's actually most correct to a C10N.

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    I'll get my head around custom faceplates at some point, although for the moment kind of dig this looking like a big Skylark.
     
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  14. Linkjr

    Linkjr Tele-Meister

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    Great build, would be interested to hear how they compare, was thinking of converting my vibrochamp to a 6g2 for more clean.
     
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  15. Drew617

    Drew617 Tele-Holic Silver Supporter

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    Hi
    Apples and bowling balls, honestly. I think you may get more clean volume out of a healthy/hot Vibrochamp with an equivalent speaker.

    IMO, this sort of conversion (less conversion than a rebuild) is mostly valuable for the sake of doing it - it's not actually economically viable and I wouldn't do it to any amplifier with much inherent value of its own. Offhand I think the commonality between a VC and a 6G2 is the PT (maybe) and cap can. Difficult to imagine that you wouldn't just be better off building the amp you want from scratch.
     
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  16. Drew617

    Drew617 Tele-Holic Silver Supporter

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    Scientifically proven, of:

    • Weber 10F150T 50W
    • Weber Sig10 Ceramic (black frame)
    • Weber Sig10S Ceramic (old green frame)
    • Weber Sig10S Alnico (old green frame)
    • 80s Emi Square Frame
    • VGS Veteran 10
    The correct speaker in this frankenstein 6G2 is the Sig10S Ceramic. It definitely prefers a ribbed/seamed cone and 1" VC.
     
  17. willholt92

    willholt92 Tele-Meister

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    That's really beautiful work, congratulations.
    I did a similar project and converted my old Fender Frontman 25 into a 5F2A Princeton.

    Faceplates will really set them off.
     
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  18. Drew617

    Drew617 Tele-Holic Silver Supporter

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    OK, the little Vibro Champ is complete. It, uh, sounds like a vibro champ. Getting about 330 B+ out of the little WRVBPT with diode rectification. The 360R was a shot in the dark based on expected B+ and puts a Sino 6V6 at about 110% max dissipation, which is appears to tolerate so far. I'm going to leave it there for now. Trem isn't working right as built, but I'll troubleshoot that later.

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