Layout drawings

[wilko]

Hey there,
I've been following along and am confused. Why all the changes? Is there no layout available that is the same as an original Marshall 18 watt? If they are so great sounding why all the revisions?

[Deadbeat2]

Alright, I found my (stupid) error. I did not swap the leads from the volume pots of each channel. DUH! Anyway, After I fixed this and a ground wire I must say I am very happy with my amp! I was never really very happy with the amp before. To me, the changes are definitely for the better. First, the tremelo channel is more forgiving with the brand of tube used. Before, I had to try every tube I had (and then some) until I found a Sovtek 12AX7WXT+ that worked the trem properly. I thought it was the lead dress at first but I could never do anything to help there. The 12AX7WXT+ was the only one that would drive the pulse of the trem without the amp motorboating. The amp would mo'boat like crazy with other 12ax7's. With a 12AT7, no mo'boating BUT the trem would not pulse. NOW, I can put any tube in there without any motorboating on any of them. Also, I found that a Sovtek 5751 made the trem work GREAT! The trem is really strong, I mean on-off. With the others it is less "throbbing". Also, before the amp has this high end sizzle I did not care for. It was like a distortion up high in the presence area of the amp. Now it has less of that until I crank the volume knob. I ended up with ; V1- JJ 12ax7, V2- 5751, V3- 5751. I am also using a Weber copper cap. Now after the changes the amp is much more balanced in it's tone. Oh, I found a cool sound while screwing around. I jumpered the channels with the trem on. It sounded like a chorus or leslie, very cool. With the trem off it was very thin, not much volume. I think this is because the channels are out of phase, correct? Richie? Gabi? Anyway, I hope this helps anybody about the changes. Bruce J.

[Plexi]

Great to hear its working like it should, and for your report/review. The 5751 ..well the older ones.. were supposed to be equal in both sides of the tube. And one reason people like them for PI tubes.


And to answer wilko, we have the layout and the changes listed,and are working on the schematic. Not as much a revision,as a correction of sorts.

If you look at other things we, or members of our forum have done, theres tons of different things we've turned the amp into.. i guess like one would take a stock car,and make it into a lowrider or whatever..

But with all the different amps and offshoots of this amp, this is finally the way the real stock 18s were built. And we finally have the layout..
the changes are for most people who have built amps with our older version.
Though it was taken some from the WEM dominator, which Jim Marshall used to copy the 18. It still had some differences. In our pic files now, you can see every connection. And now we are getting reviews of people who have made the changes to there amps, and there opinions of the difference. Its just a few wiring corrections. But it does seem to effect the amp and its sound. So this is where we are.. Hope this helps

Richie

[wilko]

That helps tremendously.
So somewhere here is athe actual file that will represent the original layout/schematic.
That's what I wasn't clear on.
Is it available now? if not, I can render a very clean schematic and/or layout using Adobe Illustrator for a vector based drawing and can write PDF's from that. If that would be helpfull, let me know.
Send me tyhe files and I can get on it.

[Plexi]

Should be here..http://www.18watt.com/Storage/L_and_D/1 ... ttilio.jpg

And somewhere i have a couple pics of just the changes
Richie

[wilko]

That helps tremendously.
So somewhere here is athe actual file that will represent the original layout/schematic.
That's what I wasn't clear on.
Is it available now? if not, I can render a very clean schematic and/or layout using Adobe Illustrator for a vector based drawing and can write PDF's from that. If that would be helpfull, let me know.
Send me tyhe files and I can get on it.

[zaphod_phil]

Well in the old version, the voltage B+ feed comes off the 100k (.05) and went to pin 6..between the pin 6 and 1 is the 220k resistor... so the voltage drops going to the other plate fed through the 220k. So when you swap..the higher or main B+ coming to the tube is now on pin 1...then goes through the 220k to feed pin 6 So it swaps the sides and the voltage of those sides will change.

OK Richie, I think I can see what you're saying. The 220k is a plate load resistor. Now, instead of the preamp half of the 12AX7 being fed it's B+ via the oscillator half's 100k load resistor, it would be the oscillator half that get's fed a reduced B+ via what is now the preamp's 100k load resistor. And the 220k now acts as the load resistor for the oscilator section. This makes a *lot* more sense than the way it used to be, as the oscillator doesn't need a huge B+ to do it's job, and in fact may be more stable without. And the preamp with it's full 280V on a 100k load resistor will work a lot better and have more headroom, etc. As some have commented, it will appear to 'breathe' more.

But now we hit a problem, since Gabi's list of mods also says:

V2 changes:
- pin 1 goes to junction R18-C16 --- used to go to junction C17-R19
- pin 2 goes to junction R23-C18 --- used to go to junction C1-R9
- pin 6 goes to junction C17-R19 --- use to go to junction R18-C16
- pin 7 goes to junction C1-R9 --- used to go to junction R23-C18

Which means the grid connections are also swapped over - so all we've actually achieved is to swap across which halves of the ECC83/12AX7 are used for the oscillator and the preamp, and other than everything is exactly as it was before in this section. So bye bye to the extra headroom and breathing tone, etc...

Now have I got something wrong here...? I sure hope so, because I like the idea of the plate load arrangement being swapped around with the oscilator, both for better tone and a more stable oscillator...

[Plexi]

.. i haven't looked back at the schematic, and hope i don't confuse you more..
But you've got the idea in the V3..so its getting better

I guess on the pedal monkey schematic or any of them, its hard to change, because it gets crossed on both ends that way. I think if you look at the old schematic.. the best way to look at it would be to just swap the cap values...or this would fix it on paper.

V2 pin is the .01 cap normal channel
pin 7 is the .022 trem channel.

And the connections going to the pots need to be swapped to make all this line up and not be crossed. Or like in the old version. It keeps everything on each side.. normal channel is hooks on the right side..and trem is to the left hookups..


But the drawings and layout we have now show exactly how they go..so maybe you can look at those . Hope i'm not confusing you more.. But i do think i see what your talking about, when you look at the old schematic, and Gabi's explaination. Gabi is working on the new layout.

And hopefully we'll have a new schematic soon too.
But as for the pedal monkey schematic, its encrypted, and only the person who drew them can make changes.. well as far as i know.
I think i sent Gabi something explaining how it is hard to describe or change the pedal monkey schematic, because the values needed changed or swapped to make it come out right.

Hope this helps clear some of it up. But again..the new layout and drawings are correct.

Richie

[zaphod_phil]

Hmmm, I'm just one of those annoying EEs who insists on a having schematic first! OK, so maybe I need to go back to the old Marshal schematic, rather than using PedalMonkey's version. I would sure love that change to the preamp load/HT to be the way it should be. That, taken with the PI tail resistor change could really make for a livelier amp...