Amp Chassis Question

Discussion in 'Shock Brother's DIY Amps' started by mjr428, Dec 4, 2019 at 12:04 PM.

  1. mjr428

    mjr428 Tele-Meister

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    So I have an old SS amp that I want to make a new cabinet for. I'm thinking about making a new amp chassis for it as well so that I can design the cab how I want it (don't think the original chassis will work because of the slanted face). I was thinking about maybe using a combination of wood and aluminum to make the chassis, or maybe make it entirely out of wood. Is there any reason that I couldn't make the chassis entirely out of wood? Is there anything that I should look out for? Any advise is much appreciated, thanks!
     
  2. drneilmb

    drneilmb TDPRI Member

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    The only thing to watch out for with a wood chassis is that you are giving up some shielding and grounding functions that the metal chassis provides. An easy way around this is to coat the inner surface of the wood chassis with copper foil like we often use for shielding guitar cavities. If you do decide to shield it with copper foil, you need to make sure that you also connect the ground points to the foil.

    Here's my first tube amp build. It's got some hum so I'm considering a top for it with copper tape shielding inside.

    1202191540a.jpg
     
  3. Snfoilhat

    Snfoilhat Tele-Afflicted

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    A complete circuit can run on wood -- like on the original breadboards of circuit design. But the metal chassis provides strength for mounting heavy parts like transformers, and the enclosed box shields the circuit from the electronically noisy environment.

    If you look at inexpensive amps of the 50s and 60s, you can see examples of very simple hybrid metal/wood chassis in production amps that start as a simple piece of sheet metal with maybe one or two folds to make a flat tray and a 60-90 degree face for mounting controls.
    Screenshot from 2019-12-04 09-37-00.png

    Here's an example I just saw on Craigslist. Unlike a tweed Fender where the chassis is a 5-sided metal box with one face open, this is more like a pair of metal trays.
    00909_gsoLbuHuNUe_600x450.jpg
    00x0x_fPapSKiorfD_600x450.jpg
     
  4. King Fan

    King Fan Friend of Leo's

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    ^^^ I like what @Snfoilhat says. And yeah, there's something to be said for making your own chassis. Uncle Doug has a video where he makes a chassis that glides out like a drawer. Handy!

    But there's also a case for buying a new chassis from a small shop, or finding an old one on eBay or the side of the road. How big an SS amp are you rehousing? A VibroChamp or PR chassis are often re-purposed, but many other options exist.
     
  5. tubelectron

    tubelectron Tele-Holic

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    Hi @mjr428 ,

    I used this kind of wood/metal combination for Hi-Fi amps with success. Here below, the sides are made from 20mm waxed Oak wood and the chassis is steel (coppered, chromed and polished) :

    [​IMG]

    But Hi-Fi power amps like that have very little gain (input sensiviy 0.5 to 0.7V RMS for full output power) compared to most of the guitar amps (2 to 70mV, to give a rough range of sensivity).

    IMHO, a complete wood chassis would be doable only if you intend to build a small and simple guitar amp circuit without high gain, I mean : Gibson GA-5 / Les Paul Junior, Fender Champion / Champ, and if you wire all the connections as short as possible (like in a Ham/RF receiver).

    Otherwise, you may front noise, hum, RF disturbances, sonic or ultrasonic oscillations due to the abscence of any shielding, that may be difficult to impossible to eradicate... o_O

    I absolutely discourage you to go for a wooden chassis if you are thinking about an amp circuit with gain ! :eek: You would be much better advised to find an aluminium chassis (cheap ones are available today), or at least re-use your solid-state amp chassis if it is convenient... ;)


    As an example, you can see below my Radio-Tone little tube amp. I made the chassis from 1.5mm aluminium and the cab from 10mm cheap Oukoume plywood (3mm for the back) :

    [​IMG]

    You note that the chassis has a minimalist special shape due to the size of the amp, but it is made from aluminium, and thus provide enough shielding to the circuit, which by the way has little gain (6GW8/ECL86 single tube).

    [​IMG]

    [​IMG]


    A short sample of my Radio-Tone, at sweet spot, with my Squier Std Strat and a touch of EHX Cathedral Reverb :



    I think that - at least - a combination of 1.5 to 2mm aluminium (sheet bent to form frontface, top (or bottom) and backface) plus 2 wooden sides (10-15mm cut to dimension and shape and screwed on chassis) would be a better way to go than full-wood chassis.

    But it's me, OK ? :D

    Good luck ! ;)
     
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  6. drneilmb

    drneilmb TDPRI Member

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    What a lovely little circuit. I was wondering about a single ECL86 guitar amp. That would be fun as a micro head using a DC-DC up converter. Do you know how much power/current the ECL86 takes in this case?
     
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  7. Preacher

    Preacher Friend of Leo's

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    First, you can bend your own chassis if you have a large enough piece of angle iron, a couple of heavy duty C clamps, a nice big hammer and a lot of patience you can make your own.




    The other option is to buy a deep straight sided cake pan.

    [​IMG]

    https://www.webstaurantstore.com/at...MI7N20qOOc5gIVsY1bCh1vugokEAkYCSABEgKpkfD_BwE

    For less than $20 you get an aluminum pan (easy to bend the flanges) that you can cut and shape to your hearts content.
     
  8. jtcnj

    jtcnj Tele-Holic

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    The cake pan thing is a good option; fairly easy to shape and fab as needed.

    I fab my chassis out of old elec / alarm panel enclosures.
    Not very difficult, not pretty naked but can be ok with face plate.
    Still need to build head cab and finish the face plate for this one. 6G2
    (A year later)

    20190909_191253.jpg
     
  9. tubelectron

    tubelectron Tele-Holic

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    Thanks @drneilmb ! ;)

    No, I do not have the datasheet values in mind now... :oops:

    My schematic gives all the useful DC values measured on the amp itself. Have a look to the ECL86/6GW8 datasheet for complementary information. The power output of my Radio-Tone is 2.5W RMS at clipping onset.

    Also search for the Magnatone model 411 amplifier : my schematic derives from this one.

    -tbln
     
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