martin manning wrote:The chassis has four holes for screws to attach the dog house, right? They should be close to the top and bottom edges of the chassis. If there isn't enough clearance to get a nut on the inside you might be able to put the screws through from the inside and put the nuts and lock washers on the outside. If that won't work, you could use self-tapping or sheet metal screws like Fender did (see pics below). These are sort of forced in from the outside, and cut their own threads as they go in. Since they are an interference fit they will not loosen easily.
I guess the cap board is not wide enough to mount with screws due to interference with the main board. In the pictures from Mojo's build guide the cap board looks to be the same width as the main board. Their recommendation is to tie the cap board to its backer board with zip ties, through those holes in the boards, and then use some kind of foam plastic (like adhesive-backed weatherstripping) to immobilize it within the dog house. That is reasonable, and solves the problem.
Are you saying to use screws for the dog house and adhesive for the cap board? The dog house screw holes arent that wide so it will still interfere with the board on the inside
As far as the capboard goes, I'm still using stand offs right? Then you're saying to drill 2 holes in the insulator board and use ties through the holes in both boards?
Here's Mojo's cap boards tied together, and an arrangement that might work for the board and dog house mounting. The weatherstrip is stuck to the chassis and to the dog house. The spacers between the main board, backer, and chassis are hex nuts.
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Martin, in the picture above the insulator board is raised above the chassis. If I raise it a little bit like shown wouldn't that solve my problem? Assuming I can find bolts that are rrelatively short? I don't see the issue with it raised a little? There still sbould be plenty of space inside
Yes you should be able to find short (1/4") screws for the dog house, and the cap board too for that matter. If you raise the insulator board with a hex nut then you might be good to go.
It just dawned on me that the bolts for the choke and ot are also going to interfere with the board.... ill have to try and find shorter bolts for that too. Why was that iissue not discussed in the mojo manual? Or am I missing something?
The OT screws should be spaced widely enough to be clear of the board, and the choke screws are off to the left. If you look closely at the '59 Bassman pics you can see them.
sorry for the long delay, I've started school again. I'm planning on doing the drilling this weekend but I want to make sure everything is clear to me beforehand.
I will try to find 1/4" bolts for the capboard and dog house. On the inside of the chassis there will be nuts to secure it. This causes two problems I can see right now:
1) the nuts will be only on one side of the circuit board, so roughly half of the board will be raised and thus the board will sit on an angle at the bottom of the chassis. should I drill a few more holes on the other side of the chassis and just feed some bolts through so that the board is uniformly raised?
2) i have the spacers to place between the insulator board and actual circuit board. the problem is that the screws it came with are VERY short. they are not long enough to go through the chassis and screw into the spacer. I am going to try to find longer screws to solve this problem, but are there any other solutions if I can't find these screws?
mounting of the OT/PT/choke should go fine.
I also need to drill a hole on the left wall of the chassis so i can place the ground lug used for the 120V power cord
I wasn't sure if we were going to have to wait until spring break to see how this comes out...
I guess the dog house mounting screws are located such that they will be covered by the circuit board? The thing about using screws with nuts to attach the dog house and cap board is that if the nuts are under the main board they will be very difficult to get to if you have to remove the cap board or cover, or even just re-tighten them at some point. Fender used self-tapping screws so there were no nuts to deal with. What size are the dog house mounting holes in the chassis? If they are large enough to pass a #6 screw through then you'd need #8 (at least) self-tapping screws to get a good bite, and they might start to get big and ugly looking.
The main board is supported at three points (and you could perhaps add a fourth). My thought is that you can put spacers (nuts or stand-offs) under the insulating board so it will clear the cap board and dog house mounting screws, then another small spacer (a nut is probably enough), followed by the circuit board, and finally another nut to secure it. If both the insulating board and circuit board are elevated at each of the mounting points it will stay level.
Sometimes it takes a bit of thought to figure out how to solve issues like this.
[quote="martin manning"]I wasn't sure if we were going to have to wait until spring break to sehardware storethis comes out...
I guess the dog house mounting screws are located such that they will be covered by the circuit board? The thing about using scghostrews with nuts to attach the dog house and cap board is that if the nuts are under the main board they will be very difficult to get to if you have to remove the cap board or cover, or even just re-tighten them at some point. Fender used self-tapping screws so there were no nuts to deal with. What size are the dog house mounting holes in the chassis? If they are large enough to pass a #6 screw through then you'd need #8 (at least) self-tapping screws to get a good bite, and they might start to get big and ugly looking.
The main board is supported at three points (and you could perhaps add a south). My thought is that you can put spacers (nuts or stand-offs) under the insulating board so it will clear the cap board and dog house mounting screws, then another small spacer (a nut is probably enough), followed by the circuit board, and finally another nut to secure it. If both the insulating board and circuit board are elevated at each of the mounting points it will stay level.
Sometimes it takes a bit of thought to figure out how to solve issues like this.[/quote
A 6 screw does fit very well if i remember correctly. are self tapping screws available at the hardware store? I havent used those before is it hard to do?
When you were talking about mounting the board werr you talking about feeding one largebolt through and sandwiching everythiing on top of it? Or using several small bolts?
I think the stand off method would require several bolts one to screw into the top and bottom of it
yoyohomieg5432 wrote:A 6 screw does fit very well if i remember correctly. are self tapping screws available at the hardware store? I havent used those before is it hard to do?
Yes, they are commonly available, and you just drive them in with a screwdriver. Look at the '59 Bassman pics showing the transformer side of the chassis and you will see the circuit board mounting screws poking through, and on the inside the dog house mounting screws can be seen. It's too bad those holes are that big... I don't know if a #8 will be secure.
yoyohomieg5432 wrote:When you were talking about mounting the board were you talking about feeding one large bolt through and sandwiching everythiing on top of it? Or using several small bolts?
I think the stand off method would require several bolts one to screw into the top and bottom of it
Yes, one long screw at each mounting point, maybe 3/4", as shown in the sketch above. It might be best to use foam weatherstripping to imobilize the cap board within the dog house so you don't have to deal with screws for that.
Will the output transformer bolts be clear of the board?
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After studying the Mojo pictures some more, my suggestion is to mount the dog house and OT with the shortest possible machine screws, using nuts and star washers. Then raise the insulating board on stand-offs or nuts just enough to clear them, which means 1/4" or less. The board material is flexible, so it won't matter if you don't raise it completely clear of the screw ends. You'll have to be sure to identify the B+ and ground wires coming from the dog house, and that they are long enough.
martin manning wrote:After studying the Mojo pictures some more, my suggestion is to mount the dog house and OT with the shortest possible machine screws, using nuts and star washers. Then raise the insulating board on stand-offs or nuts just enough to clear them, which means 1/4" or less. The board material is flexible, so it won't matter if you don't raise it completely clear of the screw ends. You'll have to be sure to identify the B+ and ground wires coming from the dog house, and that they are long enough.
So why have you changed from self tapping screws? I have access to a drill press I can make smaller holes in the doghouse if you think self tapping screws are the better route
I guess we're only talking about the dog house screws here, since the OT has to be mounted with #8 screws and nuts, and I think the best solution for the cap board is to pad it in with weatherstripping.
For the dog house, self-taping screws would be authentic and all, but given that the chassis holes are too big for #6 and probably #8 screws you'd have to use #10's (too big) or drill new holes, and I'm just not a big fan of having extra holes around. There is also a down-side to self-tapping screws in that after they have been removed and replaced a few times they will begin to lose their grip and eventually they won't tighten. If the chassis material is heavy gauge steel (probably true of the original), that might not be an issue. If the dog house screws come through under the board (and unlike the original, I think they do) then you'll still have to raise the circuit board. If you use nuts, and they are only partially obscured you can probably get enough of a grip on them with needle-nose pliers so that you can tighten the screws from the other side.
Martin, I'm afraid I'm becoming more confused. So you no longer think using bolts or screws to secure the cap board is a good idea either? I don't really understand what you mean by padding it with weatherstripping. You essentially just want to pack it in but not actualy secure it to the chassis?
