Amp build for a first time builder?

[yoyohomieg5432]

i know i asked this before but I'm still a little unclear..

i'm looking at wires v1ag, v1bg. what is the a and what is the b? how did you know how to wire up the tube sockets? Is there diagrams for these somewhere you referred to?

i'm confused with the numbering on the tubes too. it looks like you added some numbers around the tube, but inside there is already some numbers. the numbers inside correspond to the labeling on my tube sockets. why did you add the external numbers?

[yoyohomieg5432]

ok, i've attached a picture of the chassis and another one of the board.

Martin, you said that we were only using 2 terminals on the ground switch but it looks like from the diagram that 3 things are wired to it? i'm a little confused with that.

[martin manning]

i know i asked this before but I'm still a little unclear..

i'm looking at wires v1ag, v1bg. what is the a and what is the b? how did you know how to wire up the tube sockets? Is there diagrams for these somewhere you referred to?

i'm confused with the numbering on the tubes too. it looks like you added some numbers around the tube, but inside there is already some numbers. the numbers inside correspond to the labeling on my tube sockets. why did you add the external numbers?

Each of the preamp tubes has two triodes in it, so they are referred to as triode a and triode b. V1a is one of the triodes in V1, the first preamp tube.

The pins on the 12A_7 series are arranged with the plate, grid, and cathode of one triode on pins 1, 2, and 3, respectively, and the other triode's plate, grid, and cathode are on pins 6, 7, and 8. Pin 9 is common to both heaters, and pins 4 and 5 are the connections to the 1-2-3 triode and the 6-7-8 triode heaters. Each heater is designed to run on 12V, but typically they are paralleled by tying pins 4 and 5 together and running the pair on 6V.

I rotated the sockets 180 degrees from the original layout so that the heater wires could be kept on the open side of the chassis, and the heater wires going to pins 4 and 5 could be run through the gap between pins 1 and 9. This keeps the signal wires on one side of the sockets and the heater wires on the other to minimize interaction. When they are rotated 180 degrees, the plate, grid, and cathode pins wind up in the same locations, so the wiring does not change.

Attached here is a 12AX7 data sheet so you can see the connections.

On the ground switch, you are using only two of the terminals. The third one (the common pole) formerly had the cap going to ground, which I x'ed out. Use your multimeter to make sure that the two terminals you are using are not shorted together with the switch bat in either position.

[yoyohomieg5432]

1)i have a question with the filter cap board: it has 2 holes in the center of the board. should i use these as a means to secure the board? or were they intended for something else?

2) on the layout it looks like there's a label close to the choke but it was overlapped by wires coming off the PT. what is this label?

3)at one point i seem to remember that you mentioned to short together 2 of the input jacks? is this correct? why?

4)is the tube wiring still the same even though the numbering has changed? i see that you modified the numbers around the tubes, but the wiring to the tubes doesn't seem to be modified so i'm a little confused with that.

5)i took a picture of inside the chassis. i just want to make sure that the orientation of the switches, etc is correct?

[yoyohomieg5432]

i added all of the wires that will be going from the boards to other places. pictures below. i'm a little worried about one eyelet, there's like 5 of 6 things that are going to be in the eyelet and i'm worried im not going to have space to push them through and if i try to push it through it's going to push other things out or loosen them.

i need to go to the hardware store again and grab some more locking washers for the transformers. should i also get them for the dog house? once i get that i can put in the PT and start doing that wiring.

[martin manning]

1)i have a question with the filter cap board: it has 2 holes in the center of the board. should i use these as a means to secure the board? or were they intended for something else?
>>>you could use those holes if they are not too big, and they are not located in a place that will cause problems on the inside. They'll have to be close to the edge of the chassis or they'll come through under the main board. All you need to do is attach the board with the insulating backer undrneath directly to the chassis so it can't move around. Four screws, with one at each corner would be even better.

2) on the layout it looks like there's a label close to the choke but it was overlapped by wires coming off the PT. what is this label?
>>> It says B+1 Ground, referring to the solder lug there.

3)at one point i seem to remember that you mentioned to short together 2 of the input jacks? is this correct? why?
>>> Hmm... I don't know what that would be about. The input jacks should be wired as shown in the layout.

4)is the tube wiring still the same even though the numbering has changed? i see that you modified the numbers around the tubes, but the wiring to the tubes doesn't seem to be modified so i'm a little confused with that.
>>> The wiring is the same. Notice the old numbers 1, 2, 3 are now 6, 7, 8, but they are still plate, grid, cathode respectively, just going to the other triode.

5)i took a picture of inside the chassis. i just want to make sure that the orientation of the switches, etc is correct?
The SPDT ground switch is flipped re the layout. I would rotate it 180 degrees so the end with two lugs is near the fuse holder, and make sure the the lug that is shown as the former location of the cap going to ground is indeed the common pole and is not used. It is likely that it is, as the switches are the same ones used in the original

[martin manning]

i added all of the wires that will be going from the boards to other places. pictures below. i'm a little worried about one eyelet, there's like 5 of 6 things that are going to be in the eyelet and i'm worried im not going to have space to push them through and if i try to push it through it's going to push other things out or loosen them.

i need to go to the hardware store again and grab some more locking washers for the transformers. should i also get them for the dog house? once i get that i can put in the PT and start doing that wiring.

Which eyelet?

Yes, use lock washers for the dog house. Usually the star type is used, probably #8, but you'll have to confirm that.

[yoyohomieg5432]

i had a left over #6 screw and it fit perfectly with the doghouse. the problem is that it was like 3/8" length i believe, left over from what is used for the tubes. it sticks out quite a bit on the inside of the chassis. is that insulator board supposed to lay right on the bottom of the chassis? or is there supposed to be some clearance? (is there two layers of standoffs?)

[martin manning]

I was thinking that the insulator board would be on the chassis surface. You could raise it, but that might cramp other things.

[snuffy]

Backing board should be on chassis floor, followed by 1/4" standoffs.Mount main board to standoffs. Space is tight on this build,so you don't want main board too high. If you use screws and nuts for the doghouse and cap board it will interfere with the backing board. I used the same chassis and tapped cap board/doghouse holes, not requiring the use of nuts that way. Hope this helps.

[yoyohomieg5432]

I was thinking that the insulator board would be on the chassis surface. You could raise it, but that might cramp other things.

If it's on the chassis surface I don't understand how securr the dog house.

Snuffy mentioned tapping? I don't really understand what that means though.

The biggest issue right now is how I am going to secure thr dog house to the chassis. I cant see a way without having to raise the insulator board.

[ampgeek]

Tapping description here:

http://www.diynetwork.com/how-to/tappin ... index.html

The final machine screw length could be chosen to not protude (much) into the chassis.

Good luck,
Dave O.

[yoyohomieg5432]

Tapping description here:

http://www.diynetwork.com/how-to/tappin ... index.html

The final machine screw length could be chosen to not protude (much) into the chassis.

Good luck,
Dave O.

So basically you just screwed it into the chassis? The chassis is pretty thin it seems like it wont be very secure? And wouldn't the screws come out prettt easy?

[martin manning]

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.

[martin manning]

On the adhesive-backed weatherstrip material, you should be able to find it at a hardware store in a roll. I'm not sure how much space you have to take up inside the dog house, but I'd guess 1/2" thickness and 3/4" width would do it. Maybe put two parallel strips on the chassis (running the long way) and a third on the inside of the dog house running in the same direction, centered so that it hits the cap casings in the middle. BTW, that stuff is handy to have around if you build effects pedals, too.