Brown Box (vintage voltage adapter) build...

Discussion in 'Shock Brother's DIY Amps' started by King Fan, Jul 7, 2020.

  1. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Many of us have seen the great info by @robrob on building a bucking transformer to drop B+ to at or near vintage levels. A nice 1998 article by R.G. Keen on the "Vintage Voltage Adapter" explains how it works and shows a couple of options and useful schematics.

    I've thought about this for a long time, since I've built three tweeds, a brownface, and two blackface-era amps that were not born to run on 120+VAC, and even with lowered-HT power transformers I was often higher than schematic on my B+.

    Rob very helpfully shows how to build one in a 3-gang plastic switch box, which is handy since you really want a duplex outlet cover -- and I couldn't figure out how I'd do that if I used say a Hammond chassis.

    As suggested by Rob and Mr. Keen, I wanted a duplex outlet with wall voltage on one receptacle and switchable, reduced voltages on the other. As Rob advises, I used a Hammond 166N12B (12 volt 4 amp) transformer.

    The hardest thing was actually finding a 3-gang wall plate laid out blank/blank/duplex. Even if I could find one, the standard plastic wall plates are very brittle, and I wanted a power switch *and* voltage selector switch *and* power indicator light, and it would be handiest if they were on the front/top, and drilling holes in a brittle plastic switchplate would be both difficult and pointless. Top tip -- an outfit called Mulberry Metal Products makes steel wall plates in blank/blank/duplex. The only problem is sourcing one. I finally found a retail source, but they took three weeks to ship, so I'm not recommending them.

    Being metal, and having the switches and lamp mounted on it, I decide I'd better have a ground anchor on the wall plate. Luckily, it turned out to be nice and rigid, yet easy enough to drill. Drilled 1 x 11/64" for the ground anchor, 1 x ¼" for the mini-toggle, and 2 x ½" holes (light and power switch) -- the latter are easier with a step drill. Note clamp...

    VVA - 1.jpeg

    The plastic boxes often come with 'nailing ears' to mount on studs, but those're super easy to cut off with a hacksaw. I suggest you compare boxes for total cubic inches -- a bit deeper and roomier makes this project easier. Recall a standard Heyco strain relief doesn't require a 'double-D' hole -- they also fit in a 5/8" round hole. That's an extra great reason for a step drill, which also makes the hole both tidy and easy. Note blue tape 'depth guide.'

    VVA - 1 (1).jpeg

    I used a beefy SJT cable which even more than SVT really rewards your imitation Heyco strain relief pliers...

    VVA - 1 (2).jpeg

    Also drilled a few 11/64" holes for #8 mounting bolts. The transformer takes up a surprising amount of space in the box, but arranging the primary and secondary leads just right let it sit flush on the floor between the Romex wiring 'doors.'

    VVA - 1 (3).jpeg

    I was going to use a Fender style fuse holder, but found there was room for the inboard kind instead. And this one on Amazon came with screw-down wire clamps -- Rob points out we're doing wall-style wiring here, and I decided less soldering was in order. With a 4A transformer, Rob notes you should use a 4A slo-blo fuse.

    VVA - 1 (6).jpeg
     
    Last edited: Jul 7, 2020
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  2. gusfinley

    gusfinley Tele-Afflicted

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    Looking good King Fan. I need to build one of these after I get my core amps up and running.
     
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  3. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    The space hog transformer and the duplex outlet in the 3rd gang means you have to think about where to put the other bits, like light and switches. Here's the layout I finally adopted.

    Brown Box layout 4a.png

    I decided a standard Carling 'Fender-style' SPST toggle would fit well and handle the work here, and the voltage selector is a standard Carling SPST mini-toggle. The indicator light is neon, 120VAC, also from Amazon, and like the switch mounts in a ½" hole.

    As Rob points out, you want to break (with a needle-nose) the tab that links the *hot* terminals on the outlets,

    VVA - 1 (5).jpeg

    but leave the tab intact (circled) on the neutral side.

    VVA - 1 (4).jpeg

    As Rob also points out, you can use wire nuts here -- this is a wall box, so that's totally NEC, and makes clobbering 3 or 4 wires together pretty easy. If you're going to take this on the road, or otherwise subject it to vibration, Rob's option of tag strips would probably be smart.

    Now a photo of all the wiring in place, with the wall plate holding the switches, lights, and ground anchor, is not very useful. So let's cut ahead. Here she is buttoned up.

    VVA - 1 (7).jpeg


    VVA - 2.jpeg
     
    Last edited: Jul 7, 2020
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  4. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    When I first fired her up, the voltage went up instead of down, even though I'd tried to pre-test the primary/secondary phase using a 9V battery. Oh, well, swap the secondaries. Rob has a tip about the diagonal 1° and 2° leads, but that didn't work out for me (if I'm seeing straight). So just leave 'em long enough to swap.

    My DMM says I'm getting a stepped-down 115 and 107VAC with the wall at 122 today. My cheap Chinese LCD meter reads nearly 3V low, but it's a consistent offset, so I can do the correction.

    VVA - 1 (8).jpeg

    VVA - 2 (1).jpeg

    VVA - 3.jpeg

    As you can see above, I plug a power strip (with the LCD in one outlet) into the 'brown box' so I don't have to swap the amp plugs in and out and so I know what voltage I'm on (I also set up the switch so 'toggle down' is 'lower').

    So far it's good for all my amps and amazing for the brown and tweeds. The ~115 setting, with my 'lowered' HV PTs, puts me eerily close to schematic on all of 'em, and they sound *great* there. I was actually able to heat up the bias a bit on the 5G9, which sounds perfect at its schematic B+ of 370. The self-biasing 5E3 and 5F2a, left alone, just sound 'sweeter and tweedier'. The 6G2 is also very happy on 115 -- it has that strikingly low scheme B+ of 315, which it was slightly above, and just sounds 'right' now. And the VibroChamp, even with my already-knocked down B+, also sounds on 115 like it's saying, "that's what I've been waiting for."

    The PR is nice on ~115 too, slightly warmer and sweeter, but I haven't re-biased. I suspect I'll just go from 115 to 122 as my ear says on the day.

    The ~107VAC setting is fine for the tweeds, but sounds a bit less 'lively.' Good for after hours blues stuff with a snifter of Hennessy, I bet. The 6G2 and especially the PR find ~107 a little too tame -- just lose their edge -- though as I say I could probably re-bias. But the whole point here is to have options at the flick of a switch. Happy camper!
     
    Last edited: Jul 7, 2020
  5. decsnspace

    decsnspace Tele-Meister

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    I actually just finished building one of these myself using an aluminum enclosures I found on Amazon. I was able to use my punch set from harbor freight to cut out the holes for the outlet to mount to (same as punching tube sockets). The bucking transformer mounts perfectly to the bottom of my 5E3 cabinet (FYI, it is slightly too large to fit a champ but works great in a deluxe or lager cab). It does add a few pounds to the cabinet but should do a good job at keeping my 5e3 from burning up. https://www.amazon.com/gp/product/B07VSMXFBF/ref=ppx_yo_dt_b_asin_title_o03_s00?ie=UTF8&psc=1 20200707_160219[1].jpg
     
  6. tubegeek

    tubegeek Friend of Leo's

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    @King Fan you can't test a transformer with DC. Nice build. My only concern - did you scrape the paint off the plate, under your ground point's nut?

    I don't know why all of us don't make one of these. You have made me want to do it.
     
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  7. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Good idea, that's the bit I couldn't figure out, a punch. Were yours shaped like the receptacle (sort of double D?) or were they round?

    Building in an aluminum chassis would have advantages.

    Thanks. I recalled seeing polarity tested with 6.3V AC -- so figured 9V DC would be enough voltage, of course totally overlooking the AC/DC angle, much less the Metallica/KISS connection... :)

    It's a fun project and so far very useful (and easy to use).
     
  8. decsnspace

    decsnspace Tele-Meister

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    They're round. They're the same ones that I use to cut out holes for octal tube sockets. The hole comes out just slightly larger than the receptacle but pretty much is a perfect fit for it.
    https://www.harborfreight.com/knockout-punch-kit-10-pc-60575.html
     
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  9. tubegeek

    tubegeek Friend of Leo's

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    The problem is, you hang out with such a Motley Crüe.

    Safety repeat question: paint under ground nut? Scraped?
     
    Last edited: Jul 7, 2020
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  10. tubegeek

    tubegeek Friend of Leo's

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    Lookit the big brain on Braaaad!

    Seriously - nicely done, clever as hell.

    CHALLENGE ROUND: (Well, maybe a "Challenge Capsule Shape") With a bit of practice you MIGHT be able to push the punch partway through and get it to just do the round parts - and then maybe Dremel the straight part of the cut. You'd have to line up the pointy sections of the punch so they are at the sides and leave the rest intact, in the "just the tip" maneuver.

    We all know how well that goes though.

    Obviously I'm not suggesting anybody go out and buy the Greenlee punch that fits exactly, it's probably 200 bucks.

    Another option (can you tell you've set my wheels in motion?) would be to do the squarish style outlets and cut rectangular holes with a saw, but this is way cooler even with the simple round holes.
     
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  11. decsnspace

    decsnspace Tele-Meister

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    LOL, I struggle enough as is just to try and get level and square holes when cutting out IEC sockets. That said, I will likely upgrade this enclosure with an IEC at some point here soon in order to make plug and go a little easier for gigs and band practice.
     
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  12. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Yes, on the inside. Plus I use an external-tooth washer under the terminal ring with the keps nut on top and turn the keps so the star turns into the metal a bit. And then of course I test the plate is continuous with the ground prong on the plug. Oh, and did I mention the loctite? :)
     
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  13. tubegeek

    tubegeek Friend of Leo's

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    You're shooting for an A, aren't you?
     
  14. tubegeek

    tubegeek Friend of Leo's

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    IECs:
    Drill the corners. Dremel or jigsaw the sides a little bit inside the line. Flat file bit by bit until you get a tight fit.

    Or, you know, $200 punch.
     
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  15. tdoty

    tdoty Tele-Meister

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    Cut a rectangular hole and cover the mess with an outlet plate? I'm the simple type.

    A "decora"/"euro-style" outlet would also be easier, as @tubegeek suggested.
     
  16. jchabalk

    jchabalk Tele-Holic

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    I have one of those digital voltage displays. If you pop the back off there's a trim screw and you match it to the correct wall voltage. Check with your meter and then adjust the trim screw until it matches. I have mine on a variac - i only swing it maybe 10 volts total but it seems to remain dead on after adjustment.
     
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  17. King Fan

    King Fan Poster Extraordinaire Ad Free Member

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    Great tip, thank you! Four little screws, and I found a tiny pot. Looks likes Phillips but shallow — turned easily with a jeweler-size slotted screwdriver. For ease and safety I did this with the thing unplugged; guessed at amount to turn. On mine, 1/4 turn left took it from 2-3V low to just right.
     
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  18. 5F6Animal

    5F6Animal Tele-Meister

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    206C2CC1-FECC-4542-8313-8E831F7412BC.jpeg I built a buck transformer inside a Hammond cast aluminum chassis. Turned out great! I used the 12A heater transformer and a digital meter on the front.
     
    Last edited: Dec 18, 2020
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  19. chas.wahl

    chas.wahl Tele-Meister

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    Source for the meter? Maybe TMI, or too much guilt (constant reminder that one is using half a watt just to drop the voltage).
     
  20. jchabalk

    jchabalk Tele-Holic

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    yeah, it's a little dodgy reaching into it while it's on eh? I happen to have this small plastic flat head screw driver that fit it ok. It's cool that you can get it dialed in though. I've had mine for about a year, i should check and see if it's drifted.
     
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