Fender sf to bf baffle conversion

Discussion in 'Amps and Cabs' started by smolder, Apr 29, 2013.

  1. smolder

    smolder Silver Supporting Member

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    Since a lot of these old amps have particle board grills and baffles, and a lot of them are crumbling, I thought it might be helpful to show some work I’ve done fixing them. I’ve bought a few cabs in this state over the last few years. I think the old style blackface arrangement is not only superior, but more flexible.

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    The nice thing about the change from bf to sf is that the groove in the cab itself seems to be similar if not the same.

    Also, I’ve done this with a minimum of tools... and in particular minimal use of power tools. You can do this in your garage or basement without any heavy lifting or complex skills. The three I have done have been easily accomplished in a Saturday morning.

    First remove the old grill. Then I use a coping say with a medium wood blade and cut from the center speaker hole out close to the edge near the cab. I cut up through the upper center section twice, then both left and right, and two cuts downward. Finally, I cut from the cent to the corners. The old particle board cuts very easily and style isn’t an issue. Slowly move the individual parts forward and backward and the pieces will come out pretty easily. On a rare occasion I’ve use a rubber mallet to get them started. You might need to use a chisel for a little leverage at the base to pry them out of the groove. The gentler you work, the cleaner the board comes out and the less work you’ll need within the groove.

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    When you pull the sections out you’ll find they are put in place with long staples. You can cut them off, but I prefer to pull them out. This does compromise the wood a bit - down to the tolex, but it rarely removes much of the wood. In case it does, mixing a bit of saw dust or particles in elmer’s glue makes a fine filler and patch.

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    Once the pieces are out a wood chisel is an excellent tool for cleaning out the groove and removing any remaining particle board... you want the groove pretty smooth, but it’s not critical to get it perfect.

    On smaller amps the grove is just under a half inch and a 3/8 inch chisel works great. On larger cabs a 5/8” works well. I use hardwood readily available from home depot for the supports on the sides. Mine sells both 1/2 x 1” and 3/4 by 1” in 3 foot lengths.

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    Cut the pieces you need and set them aside. At this point I use some birch plywood for the front baffle. Same thickness as the supports.

    I put all of the pieces in place, including the baffle and set the speaker in for placement. On this cab I am centering a 12”speaker. I built an amp for this placing the transformers on the outer edge, so I have plenty of clearance. In my other princeton reverb I have the twelve offset to the side away from the power transformer.

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    I typically draw around the speaker, then mark the four holes I intend to use to mount the speaker with my drill. Using star nuts, I mark a place where the hole will allow them plenty of grip. i then draw the cut circle with a compass and drill four starter holes as shown. Finally, I cut the hole and file the edges.

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    Once all of the parts are cut I assemble them, place the speaker on the baffle and put the chassis in the amp to double check for clearance.

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    Once I know all the parts will fit I start gluing. I begin with the side support strips, clamping them in place. Then I take the baffle out and paint on side and all of the edges. After about an hour the two side strips are solid enough to put in the bottom parts and clamp them as well... then I paint the back side and spray the edges a second time.

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    As the support strips are drying in place I’ll tape off the tolex and the interior of the of the cab. As the strips set, the clamps can be removed, but I make sure they are pretty secure first. I then paint the strips front and back, and about twenty minutes in the sun, everything is dry enough to assemble. I live in a very dry climate so this goes pretty quick. Absolutely no harm in letting this stuff set overnight.

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    btw - you could certainly paint the parts prior to assembly and then glue it all together. I just choose to do it the other way around.

    Once everything is glued and painted, it’s time to pull off the old grill cloth. In all but the most extreme cases it can be reused and preserves whatever mojo the amp has earned in it’s lifetime. I use an old small chisel to raise the staples, then a pair of needle nose pliers to remove them.

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    The creases help it to fit. Start with the top edge and keep it straight, stapling from the center out about every three inches. This gives you room for slight tightening the second time around. Do the same with the bottom, then the two sides. The gaps allow you to come back and straighten or tighten the fabric as needed. On rare occasions I’ve had to remove and restaple. Smaller staple guns only partially insert the staples, which gives you the opportunity to easily remove them. Once I’m happy and the fabric is slightly taunt and lined up, I hammer them all the way down. I don’t bother painting the staples prior to using them, but it’s certainly an option if you want it to look period correct. In my ideal world, no one will ever see them.

    Once done, you should be ready for final assembly. I use 3/4 or 1 inch wood screws to secure the baffle to the support boards from the back. I pre-drill and countersink the holes. On the princeton I used three on each side, and four across the bottom. The beauty of the blackface style baffle is that it is simple to remove and replace... so fo a princeton, a 10” with a 12, or for a twin reverb a 15” instead of two 12’s.
     
  2. cap'n'crunch

    cap'n'crunch Member

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    Nice job! Do you notice a tone diffrence with the birch ply vs. particle board?
     
  3. smolder

    smolder Silver Supporting Member

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    Probably, unfortunately I replaced a 10 inch speaker with a 12 inch JBL D120, so the baffle would be a subtler subset of the difference in tone.
     
  4. woof*

    woof* Member

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    Congrats on your handiwork!
    Thanks also for the tutorial :)

    For those like me not so handy, you can buy a premade baffle with the correct cloth, aged even..from a couple eBay sellers and some cabinet makers like Mojo and Newell.
     
  5. hank57

    hank57 Gold Supporting Member

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    I enjoyed this. I have a Vibro Champ thatI'd prefer to have a 10" speaker in but I may be having a hard time with postponing.

    Good work smolder.

    p.s. I swear I smelled paint when I scrolled down to painting part.
     

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