diytube.com

Before I put my order in for the boards, I have a couple of questions.

1. If I understand correctly, I souldn't use a pot for the feedback because the boards are already designed for 15db gain and are tuned already. I'm a still new to this so If I had to change other values down the line of the circuit board because I want to change the feedback I wouldn't feel comfortable just yet.

2. If I wanted to use the a 5751 / 6CG7 combo, would I use Ned's version for the values or the standard version.

I'm getting a parts list together so I need to know what to order.

Thanks,

Jason

1) If you want to mod the board later on, you could just lower the negative feedback some to assure stability.

2) I think Ned's values are optimized, but I haven't tested it.

I built a pair of Poseidons per Ned's schematic. I fully intend to run the 5751 in the first stage and a 12BH7 in the LTP as recommended by Ned. That's assuming, of course, that I ever get around to finishing building the thing.

Before I started soldering, I tried to sketch out the load lines for the small signal tubes. I did all the work by hand on printouts of the tube curves. If I can find them, I'll try to scan them in and post them here. I think I came to the conclusion that Ned's recommendation for component values is slightly preferable for the 5751/12BH7 combo. It runs these tubes in a slightly more linear part of the load line.

The difference wasn't much, though, and I think Shannon's schematic would work just fine with the 5751/12BH7. I also believe that Ned's schematic would work equally well with the 12AX7/12AU7, should the need ever arise.

So the 6CG7 will work in either configutation right?

I'll just leave the feedback as is.

I'd imagine so. You've already addressed the pin differences for the heater, correct? (pins 4, 5, and 9)

Well let me see if I can get this right. I took me an hour to come up with this........If I use the 6CG7 in place of the 12AU7, I disconnect the jumper going from pins 4 & 5 to 9 because on the 12AU7, this would be the center tap (9) and there is no center tap on the 6CG7. But on the 6CG7, it says pin 9 is for an "internal shield". What is that and what would it connect to ,nothing?

I think Shannon explained it well here:
http://www.diytube.com/phpBB2/viewtopic ... 61&start=3

The pin for the internal shield could probably get tied to ground, if you like.

Well I don't get the cutting of the two x's on V2 but I'm sure I will once I get the boards in hand. I put my orders in for the boards, so I'll see once they get here.

Thanks

Look at the photo of the underside of the board in Shannon's post here:
http://www.diytube.com/phpBB2/viewtopic ... 72&start=3

It's the second photo in his post. You can see the two traces marked 'X' near pins 4 and 5 on V2. You just cut through them with an Xacto knife. Use your meter to make sure they are cut. I sometimes make two cuts about half a millimeter apart, then use the tip of the knife to scrape away the copper trace in between the cuts.

Since you haven't yet built the boards, you might also want to read up on your options for V1:
http://www.diytube.com/phpBB2/viewtopic ... 61&start=1

You're looking for the part where Shannon says "you can cut the 'X' at V1 and rotate the socket at V1 180 degrees".

Ah, I read that before and it wasn't clicking with me. Now I do, just cut the X's on one of the driver board for the V1 slot and rotate 190 degrees. That is a pretty cleaver idea.

I thought my order for the MK III boards went through but I guess they didn't. Who has them in stock and where should I send the money to?

Thanks,

Jason

Did you try Triode?
http://store.triodestore.com/diytubemk3.html

Does Shannon sell these directly?

I could try again. But who all sells it?

Triode Electronics sells them and I do, too.

Before hacking up the board, I'd recommend using the 12BH7 as a drop-in sub for the 12AU7. The 'BH7 sounds very similar to the 'CG7 (a little better, IMO) and much better than the 'AU7 (in a lot of people's opinion). Since there's no surgery involved, you can decide for yourself much more easily.