4-4-0 build - done 2-14-15...happy Valentine's Day!

[johnnyreece]

So...one of my upcoming projects is going to be a 4-4-0 build, but in a full-size express chassis (thanks, RJ!). Instead of using a single 6SN7, I plan to use two 6J5 (1/2 of a 6SN7). I don't plan on using a can-cap; rather, I'm going to go with the standard 'wreck cap stack (I'm cheap; what can I say?). Does anyone see a problem with using a more 'wreck-style layout as opposed to the AX84 version? I'm still really in the early-planning stages, as there's other stuff ahead of this, but I'm relatively excited to see what happens!

[RJ Guitars]

I had thoughts of this at one time - although I was thinking more of the Rockster circuit than the Express in those days. I had scored some old 1626 Triodes that were the magic behind the Darling 1 watt HiFi amp and I wanted to use them in a Wreck build for another low watt amp. They have a 12V filament and I think that factor alone has kept me from doing anything further... seems like the wiring all matched up otherwise with a EL34.

I'll give you a couple pieces you can take or leave for what they are worth. The small amount of work I did on the schematic for the triode output section and then a clean canvas that might be useful in putting together your layout. When you are all done I can put it into CAD if you don't have those tools and you want to share it. No doubt Mr. Fowler will be on this in a heart beat and let me know it would be O.K. to get rid of the unused holes in that perf board...

[johnnyreece]

Thanks! This is the kind of stuff I get to work on while my wife watches Survivor. I appreciate the head-start! I'll probably use DIYLC for the layout eventually, but your file will be good for hand-drawing it first.

[RJ Guitars]

Yeah, just don't let her to skillful at that survivor stuff... could be detrimental to your health

[romberg]

I have some dxf files for the layout of the chassis and board for this little 4-4-0 I built a while back.

http://home.comcast.net/~mike.romberg/a ... index.html

I sorta based it on the ax84 layout and squished it all into a smaller chassis. I did not have any layout related issues. So, I think your plan should work fine.

Lemme know if you are interested in the CAD files and I'll dig 'em up.

Mike

[Mark]

What size is your chassis, I thought the AX-84 chassis was a bit big for a two watt amp. It came out looking quite good. Who did the cab for you?

What speakers are you using for this amp?

[johnnyreece]

Mike - Thanks for the offer, but I don't think I have a program that can open that file type. Those are great pics, though! I'm sure I'll spend more than a couple minutes looking at that when I put mine together.

Mark - I don't know what size the AX84 chassis is, but I'm betting this will be bigger. I'm using a full-size Express chassis. Of course, I'm also using one more tube than the standard 4-4-0, so that will help to take up a little of the extra space.

As far as cabs, I'm not sure what I'm going to do yet. I'm thinking I might build a standard Trainwreck-style cab, but that could change. Whatever I do, it will, most likely, end up as a head. I've got a few speaker options, but none are extremely special. Got an Eminence 12" of some variety that I've forgotten, and 3 Weber signatures: 12B Ceramic, 10S Alnico, and 8S Alnico. I've really gotten into head/speaker configurations instead of combos lately.

[johnnyreece]

Well, now that I've finished up what I was working on for everyone else, and my Magnatone clone is up and running, it's time to get going on this monster. I recently grabbed some 12AV7's for cheap, so I'm thinking of trying them in the PI (specs call for a 12AY7). Curious how that will turn out. I'm working on getting the layout complete, and it should look very Trainwreck-y, with some minor differences. I'll keep everyone posted!

I also salvaged some WIMA caps from a PCB amp. I might try to slightly modify my layout to fit those on. There isn't much in the way of leads to work with, but hey, I'm cheap.

[romberg]

I recently grabbed some 12AV7's for cheap, so I'm thinking of trying them in the PI (specs call for a 12AY7). Curious how that will turn out.

I put a 12ay7 in the PI on my build too. And... I did not like the way it sounded. Too wimpy. Putting a 12ax7 in it's place fixed it. Your tastes may be different than mine but you might wanna leave the option open to put in an ax7.

Mike

[johnnyreece]

Right on. I suppose I have plenty of each. We'll see what happens!

[johnnyreece]

Weeell...in checking data sheets I may have a problem. Max plate for a 6J5 is 300, not 350 like the 6SN7. I may have some more design work than I'd planned...

Edit...fixed tube name...too used to putting a 7 at the end of everything...

[johnnyreece]

Okay, layout created. Probably going to take some tweaking as I dial in voltages. I assume my dropping resistor string might change a bit, due to the lowering of my B+. Will probably attempt some version of the MOSFET/Zener drop. Also haven't double-checked for accuracy yet, but will do before solder hits the turrets. Will update as it progresses! Unless no one cares, then I'll probably just move on to the next project.

[RJ Guitars]

Okay, layout created... Will update as it progresses! Unless no one cares, then I'll probably just move on to the next project.

Yeah, that's not gonna happen. This is one of the coolest projects going right now. Looking forward to the most mundane of details in dialing this in. I expect it to be a really fun amp and a prototype for many triode output Wrecks in the future. Great looking layout, thanks for sharing that!

[romberg]

Are you using a 6J5 or a 6J7? It looks like the 6J7 is a pentode. But your layout mentions
6J5 (which does appear to be half a 6sn7). I would guess that the pentodes would require a different OT?

Does anyone even make 6J5s anymore? I suppose it would not be too hard to rewire it if you had to switch from them to a 6sn7.

Mike

[johnnyreece]

It is 6J5. It's still basically a 4-4-0, just with the dual triode split in two. I don't know if those are still made or not, but I have a small stash (thanks RJ). If it ever gets to the point where I can't get them, I could always rewire a socket as 6SN7 and call it a day.

And, RJ, thanks for the interest! My hope in putting stuff like this together is that someday, someone will use it. I can't give back much in knowledge, but hopefully, at least I have some decent documentation.