PCB Layout

[dsavitsk]

Quote:

Originally Posted by skyskraper oh cool, wasnt sure if the software did that is there a particular reason for that exact board size?

So long as you use this particular size, you get 3 boards for $51. Any change and it gets way more expensive.

 

[skyskraper]

oh i didnt realise u were up to that threshold sorry

 

[dsavitsk]

fixed. I also fixed a small bug -- if you look at the earlier versions, the B+ pad was connected to ground. oops.

 

[Voodoochile]

Quote:

Originally Posted by dsavitsk I have done a few point to point projects, and I did this one with pencil and paper about 8 different ways until I hit on something that seemed promising.

Well that's cool. I'm very glad to hear it. Too many people just plop down parts on a 'board' in a program like this, and just drag them around until they can make the ends connect the way the schematic calls for. Actually fitting the parts in place, and building and listening does a lot to enlighten, so although you worked this one up mainly in pencil, at least you have already experienced the breadboard build. It more educational than most peeps would care to admit, IMO.

Again, it is looking good.

 

[dsavitsk]

I put up a little page for this project at http://www.ecp.cc/cathode_follower.html. You can download the board files there (the link is near the bottom). My sense is that 6DJ8 tubes can be run successfully with a B+ of around 80-90V which is a little easier to deal with than the 285V that MJ suggests for the 12ax7. I am going to start thinking about an appropriate power supply, and perhaps look into actually doing this project -- probably in the late fall if at all.

 

[MisterX]

I am missing something here....
What kind of caps are you planning on using for C2?
I am asking because your B+ and PG inputs seem like they would be burried if you use say big solen caps there.

Think you might need a Pot ground?

 

[Born2bwire]

Quote:

Originally Posted by MisterX Think you might need a Pot ground?

He's got two of the pot's pins grounded.

 

[dsavitsk]

Quote:

Originally Posted by MisterX I am missing something here.... What kind of caps are you planning on using for C2? I am asking because your B+ and PG inputs seem like they would be burried if you use say big solen caps there.

On a board this small, there is no room for big film caps. Thus, the idea is that they are under, or next to the board (like what Ron Welborne did here http://www.welbornelabs.com/images/ultra4b.jpg.) While I said Solen earlier, in the back of my head are Kimber's which have long wire leads which would get them a sufficient distance away that they should not get in the way of the B+. I agree, however, that placing the B+ there is a bit of a conflict with the cap, but unless someone can come up with a better place, I think itis the best choice.

Quote:

Think you might need a Pot ground?

The alps pot's shaft should ground itself on the case (yes, a metal case seems to be required, and as I tend to machine my own panels, anodization is not a problem for me), and two of its legs are grounded. You need more? You could also run a wire from the grounding screw to, um, well somewhere. How about the second input ground? You really only need to run an input ground wire to one of them.

-d

 

[MisterX]

Quote:

On a board this small, there is no room for big film caps.

I understood that part..... but the mounting the caps under the board thing was not all that clear so I asked.


Quote:

I agree, however, that placing the B+ there is a bit of a conflict with the cap, but unless someone can come up with a better place, I think itis the best choice.

Run the trace under R6 and out the back of the board?
But that is not exactly a great solution either.... unless you rotate the R6s but that opens up a whole new can of worms doesn't it?

Quote:

The alps pot's shaft should ground itself on the case

Key word should.

But how often does that acutally happen?
You ever touched the pot or the case on an amp and had it go bzzzztttt because the pot's shaft should have been grounded by the case but it wasn't?

(I should have made the whole pot shaft thing clear when I posted that question, my bad)

Quote:

How about the second input ground?

That would do the trick

 

[Voodoochile]

Quote:

Originally Posted by dsavitsk My sense is that 6DJ8 tubes can be run successfully with a B+ of around 80-90V which is a little easier to deal with than the 285V that MJ suggests for the 12ax7.

I've seen it (6DJ8) used as the front end of a tube/mosfet amp running with 70v B+ with very nice results.