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

[romberg]

I am still surprised at how loud this bugger is through a 10" speaker.

Yea. I did a rough measurement on mine and 2 watts clean is ballpark. Of course it cranks out more when set to kill. Which is the normal mode of operation. I have to put mine on an attenuator.

Mike

[johnnyreece]

Okay, one new pic, and then I'll shut up until it's done. Faceplate turned out well, I think!

[IMG644]http://i218.photobucket.com/albums/cc165/moto_xxx199/Amp%20designs/629f0bfb-2014-4858-81c4-8f36861972de_zpsa059a4c9.jpg[/img]

[johnnyreece]

Alright, here it is. All finished and ready for the ball. I have to say, there aren't many clean tones to find on this low-watt beast, but the distortion is oh-so-sweet. I was using my Les Paul, which might account for some of the no-headroom-ness. Tubes are (pre to power) 12AX7, 12AX7, 12AV7, 6J5, 6J5. I might try a 12AY7 in the PI, as that is the valve specified in the design, but I must say, I like it just fine as-is. Someday, if I run out of suitable 6J5's, I may convert it to a 2x6SN7 for double the power, but I'm in no hurry. The point of this (for me) was to get a cranked distortion sound at lower volumes, and this is it for me. With the low power, there's no noise to speak of. With no guitar plugged in, I can't tell it's even on when fully cranked. Pleasantly surprised there. So far, I've only run through an alnico 10. Hoping to get my 2x12 back this weekend to try that out and see about coaxing some more bass out of it. I plan to eventually make a matching 2x12 vertical slant cab, but that's for another day. Without further ado, enjoy the crappy, blurry cell phone pics :

[IMG768]http://i218.photobucket.com/albums/cc165/moto_xxx199/Amp%20designs/F05DDA21-C4FF-4466-AD54-A11349191F5E_zpscta9bmoe.jpg[/img]

[IMG768]http://i218.photobucket.com/albums/cc165/moto_xxx199/Amp%20designs/6DEEDD38-0198-4E48-9B8D-F17D56A71EA2_zpsjwzhlfc0.jpg[/img]

[romberg]

Alright, here it is. All finished and ready for the ball.

Looks nice. Using a full size chassis left lots of room in there.

I have to say, there aren't many clean tones to find on this low-watt beast, but the distortion is oh-so-sweet. I was using my Les Paul, which might account for some of the no-headroom-ness.

It should clean up when you back off the guitar's volume. That is pretty much how this circuit works. With the amp on around noon and the guitar on 1 - 3 nice cleans. Crank the guitar and then defcon 1. Glen has a very nice video demoing this:

https://www.youtube.com/watch?v=Uc3Xi6aAG80

If your 4-4-0 does not also sorta behave like this maybe something needs tweaking. Mine does a clean to mean thing with the guitar volume.

Mike

[johnnyreece]

Yeah, I need to rework the controls on my LP. It turns to mud when the volume's not all the way up. There is definitely plenty of room in the chassis. Many thanks to RJ for hooking me up with that, along with the transformers and 6J5's.

[RJ Guitars]

Hey Johnny, your mention off this on another thread brought me back to take a look at this again. Do you consider it finished now?

I was wondering about the headroom in a small amp like this with the low wattage triode outputs. I think we considered the thought of reducing the signal into the output section in an earlier discussion on this thread. I have to do that on my lower wattage liverpool style builds. Without it there isn't enough headroom. Are you happy with the headroom now?

[johnnyreece]

Hey Johnny, your mention off this on another thread brought me back to take a look at this again. Do you consider it finished now?

I was wondering about the headroom in a small amp like this with the low wattage triode outputs. I think we considered the thought of reducing the signal into the output section in an earlier discussion on this thread. I have to do that on my lower wattage liverpool style builds. Without it there isn't enough headroom. Are you happy with the headroom now?

Yeah, I have a 12AY7 in V1 and a 12AV7 still in the PI. I honestly play this amp specifically for the overdrive. Part of the problem is that I'm more of a Malcolm than an Angus: I don't have much finesse. My brother played and it cleaned up quite a bit. I'm terribly thrilled, though! I may hit you up for some more parts, as my brother wants one, too. There's a few things I'll do differently, but for the most part, I think it's ready. I just picked up a batch of like 40 old 6j5's, so I'm going to try matching some up a little better.

For more headroom, it might be worth running two 6SN7's. It would probably require a different OT, unless you wanted to use a different speaker impedance. I think I'll keep mine as-is though; it does the job it was built to do.

[romberg]

I was wondering about the headroom in a small amp like this with the low wattage triode outputs. I think we considered the thought of reducing the signal into the output section in an earlier discussion on this thread. I have to do that on my lower wattage liverpool style builds. Without it there isn't enough headroom. Are you happy with the headroom now?

I'm in the process of trying splitting the plate resistors on the PI as described by Tillydog on ax84. There is a schematic over there where he uses a 55k/39k and 47k/33k in place of the 100k and 82k resistors. The coupling caps are then attached to the junction. This taps the plate loads at around 40% in order to keep the PI functioning the same way as in a big amp but drives the power tubes with a range more suitable for the smaller tubes.

I'll report back what I find if anyone is interested.

Mike

[RJ Guitars]

I was wondering about the headroom in a small amp like this with the low wattage triode outputs. I think we considered the thought of reducing the signal into the output section in an earlier discussion on this thread. I have to do that on my lower wattage liverpool style builds. Without it there isn't enough headroom. Are you happy with the headroom now?

I'm in the process of trying splitting the plate resistors on the PI as described by Tillydog on ax84. There is a schematic over there where he uses a 55k/39k and 47k/33k in place of the 100k and 82k resistors. The coupling caps are then attached to the junction. This taps the plate loads at around 40% in order to keep the PI functioning the same way as in a big amp but drives the power tubes with a range more suitable for the smaller tubes.

I'll report back what I find if anyone is interested.

Mike

Count me in - sounds like something quite useful.

[johnnyreece]

Absolutely interested! Thanks Mike!

[romberg]

Reporting back. Shorty story: It is very much worth doing.

It is not my idea and I point any that are interested here for Tillydog's pioneering work:

http://www.ax84.com/bbs/dm.php?id=436562

The following are my findings on my amp.

I've got my 6sn7 biased at around -13V. So, it starts to clip with a PI signal around 25V or so. And the signal was clean all the way through that point. When fully cranked the PI was slamming the 6sn7 with 125Vpp waves. And when the PI make the transition into overdrive it developed a funky looking lower half. My output had fairly steep looking slopes similar to Tillydog's.

After switching to 40% split plates the power tubes still clip at exactly the same point. But now when they are cranked they are only getting hit with around 60Vpp. The funny looking waves at partial clipping were gone. Finally the partially clipped output waves had a slope that resembled a sin wave.

Most importantly how does it sound? I did not think it sounded terrible before. But there is no way I'm putting it back. It does the whole clean to mean thing much better now. And the cleans are available over a wider portion of the guitars volume.

I feared this may alter/lower the gainyness of the amp. But it does not. Just makes it smoother (I think due to the slopes not being pure vertical until way cranked up). It also sounds nicer in the transition region of partial clipping.


Below are a few before and after scope shots

Mike

[johnnyreece]

Right on. Thanks for reporting back! I may give this a shot in mine and see what happens. I'm also thinking of trying a pair of 6AH4 in the power slot. I need to do some math to see if it works with what I've got in there or not, but it could very possibly give a boost in power.

[RJ Guitars]

Thanks Mike, that is some great stuff. It will take me a while to go through it all.

I've used a few of those ideas on my ~8 watt EL95 Liverpool and turned it from raspy sounding into a superb amp... however, it might just be possible to do even better??

I want to learn a little more about the split load PI technique, I haven't tried that yet but it sounds like something I wanna try.

[RJ Guitars]

Johnny, Did you post a schematic and I am blind or is it available otherwise?
I am getting started on my Triode output Express build but I haven't found much info on fixed bias for a triode output... do you have info I can borrow? thanks, rj

[johnnyreece]

I used the AX84 schematic, but instead of a single 6SN7, I used two 6J5 (and of course, the iron you provided instead of those specified in the schematic). I was going to post that schematic, but it expressly (no pun intended ) forbade that. However, I'll go ahead and link to the page: http://www.ax84.com/4-4-0.html . I've not yet made the PI changes Mike suggested, but I imagine they would be very useful.