4-4-0 [2 NEW BUILDS WITH PICS; THE 2 WATT WRECK]

[godi]

No, this not an add on my build, I just follow the circuit design by the AX84 guys, they use two independant bias pots. Howerver you can locate the pots inside or outside as I did and the power rating of 1 Watt is probably overbuild, 1/2 Watt would do the job, no problems there.

[godi]

I forgot to say that I try the amp with a single power tube and with two tubes. I can only recommend the use of two power tubes, the sound is much fuller and better with two tubes. One tube sound a little thin to my ears.

[amplifiednation]

I forgot to say that I try the amp with a single power tube and with two tubes. I can only recommend the use of two power tubes, the sound is much fuller and better with two tubes. One tube sound a little thin to my ears.

what changes to the circuit to make it with a paralleled tube?

[godi]

I could not find this information myself when I builded mine, so I try to parralel the two tubes, whitout any change, I did not even bother with the impedance change, and it work perfectly.

[amplifiednation]

So you paralleled the tubes running each half of the push pull how? Did you combine the triodes of each tube or combine triodes of each side of the two tubes?

[godi]

I understand your question, let say that a 6SN7 have a left and a right side, I parralel the left side of one tube to the left side of the second tube, same thing with the right side.

[amplifiednation]

Cool thanks.that does answer my question and exactly what I will do. Jean, what happened to your transformer? Why was it blowing fuses?

[godi]

I forgot to say this, using my suggest method, this permit you to run the amp with only one power tube for about two Watts output and if you just plug a second tube the amp will output 4 Watts. The other way around, if you parralel on the same tube you would alway need two power tubes install.

Since the first start up of the amp, I could ear the transformer buzzing quit loud, however the amp work very well for about five days, then for no reasons, the fuses started to blow, I new something was wrong with the power transformer. I've got a new on on the way from Hammond, I had no warranty problems with Hammond, plus the seller know me very well.

So I will rebuild the present amp full size since the chassis is very thick and can support the heavy transformers and I will rebuild an other 4-4-0 using a cheaper chassis using the present circuit board and my output and power transformer. I wont spend money on expensive PEC pots, I will buy Alpha or CTS pots.

[amplifiednation]

I'm getting through this build so far. I have the board built and everything mounted (almost...) I'm getting ready to run some wires.

What is the best way to mount the bias pots? I got some from mojotone but they have absoloutely no way to mount, like they need to be on a board.

I looked up the following product on mouser (jean, the one's I think you are using) but I'm still unsure how to secure them to the chassis?

http://www.mouser.com/ProductDetail/BI- ... k0rWTbA%3d

Also, for the heater wiring...the current first flows through the two 0.1R/5W restitors? Is that an artificial CT that references ground somehow or does it just pass through to the filaments and the pilot light?

[Colossal]

For the 4-4-0 ver1 keep in mind that the OT primary impedance for a 6SN7 (one tube split and running two triodes in push pull) is about 22k. The OT for this is either Cliff Chappell's custom Heyboer OT or the multi-tap Hammond 125 series. When a second 6SN7 is added, making the amp 4W in parallel push-pull, the impedance is cut in half. The high impedance was chosen because the tube is normally used for voltage amplification, not power amplification. The chosen impedance also sounded better when the amp was being designed.

Cliff Chappell (of AX84) was the original developer and has since modified the design to add the second 6SN7 if desired. He also offers a dual primary OT (one tap at 22k and the other at 11k) in a nice chunky 10W format. Builders of the 2x6SN7 design (four triodes in push-pull) have reported more complexity in the tone and improved low end. I have played the original 4-4-0 and it was a great sounding amp and surprisingly loud. A lot of effort was put into tweaking the PI to get the amp to react properly, swelling into feedback, like a real Wreck.

Have a listen here:
http://www.chappellamps.com/amplifiers/ ... _2_197.mp3

[img:350:261]http://www.chappellamps.com/gallery/4-4 ... so_med.jpg[/img]

[amplifiednation]

Colossal,
Thanks my man. I decided on the second output tube after buying my parts, so I have the hammond multitap 125c. Some of the users said they were able to get everything to work properly without changing the impedence?

Is that true or false?

I'm excited to get the amp up and running. It's my first fixed bias build so I'm trying to figure out how to mount these pots.

[amplifiednation]

I have one ceramic cap missing from the board and need to get the control side of the amp wired up, but I pretty much finished with the sockets.

I might ditch the second 6SN7 tube for now, it's all wired in for the most part. I still gotta figure out the fixed bias (my first fixed bias amp)

[amplifiednation]

I tried to keep this amp nice and tidy but there's a lot going on in this 16 inch chassis. I'm waiting on some coax to come today for the first stages of the preamps.

Thanks to fellow member onewithnot that helped me by etching me a small PCB to mount my bias pots on. I drilled out the chassis entirely by hand and I wished I had given myself a little more room. 2nd build and still learning...

My build is not nearly as neat as some of the others but I tried to be mindful of lead dress. I'm hoping to power up later today via limiter and hopefully have a working 4-4-0. (really hoping)

Taywreck?

[Cliff Schecht]

Taylor your lead dress would improve if you could move the board over about 2". What you have could be cleaned up by hiding a few of the wires under the board (the bias run from the pot to the board for example) and shortening the wire runs to the preamp tubes. I've become a fan of using small gauge wires on anything that doesn't carry lots of currents simply because it looks neater and makes troubleshooting less of a headache. It also makes wiring the tube sockets a bit less of a chore (you don't have to try to mangle 50 wire strands into a tiny hole). I'm afraid the long parallel wire runs from the preamp board to the first few pots (green wires) might also be a trouble area for you. Anybody who has built an Express or two knows that this is a very touchy area when it comes to lead dress and getting lazy here can result in nasty oscillations.

As usual I'm not trying to be uber-critical but am trying to provide some helpful and constructive criticism .

I spend a LOT of time now with a pad and a pencil just planning out the insides of the amp, drawing up layouts until I get something that looks good. There's always a wire or two that will cause you some issue but again, this is where how much planning you do beforehand will determine how good the final product looks.

Once you get a few builds under your belt you will get better about planning stuff out. The experience that one can only get from sitting down and actually building an amp is invaluable however, otherwise you can never plan in future builds to fix problems that you only would have found from actually building. Here is a thread on two Rocket's that I built: https://tubeamparchive.com/viewtopic.ph ... ght=rocket. Notice in the smaller one how well the preamp board lines up with both the sockets and the pots (ignoring the fact that the whole amp was drilled backwards from a normal Rocket ). This is not to pimp my own build but I think I did a good job of planning this one out before I touched anything with a drill (only after I cut out the laydown power transformer hole on the wrong side of the chassis of course). TBH this amp had problems too but nothing that was associated with layout (I think one of my coupling caps is leaky still, I've already replaced the Japanese paper in oils and the amp still has a weird harshness on the G and B open strings).

[amplifiednation]

Yeah the rocket was a little easier to do lead dress because there were so many pictures to follow. This 440 it seems like a lot of people have built, but not as many pictures are easily found.

Finished the build and tried to get it going. Got 125 mains but no juice going into the amp. Thats with the limiter on. Guess my first problem is a lot bigger than i thought it would be.