My Express build - help and feedback appreciated

[Mulder]

Hi fellow TAG members,

I am pretty new to this forum and I have loads of questions. I have been reading a lot already, but new questions arise everyday. Since I am new here, a small introduction isn't misplaced. Like all of you, I play guitar and I have a big interest in electronics. Currently, I study electrical engineering at the Delft University of Technology in the Netherlands. However, tube electronics are not part of the curriculum. So the best place to learn more about it is by discussing it on a forum like this I am very motivated to learn more, and all the feedback I can get is welcome!

I would really like to build an Express, but with a couple of additions. I have found different bits and pieces of information and ideas on this forum, but I am stuck at the implementation of them.
I have attached a drawing I made this morning of my schematic. I hope it is clear enough. My handwriting isn't the best.
For now, it is more or less a '90 Kelly with UR12's revisions. The power supply has been taken from the Ceriatone layout, since I wanted to use F&T caps. I have also added some resistors without any values on the grids of the pre amp tubes. I have seen some schematics put a resistor here, I guess for some slight attenuation. I don't know if I will use them or not, but I wanted to make a layout that can easily be modded. I also added the LaMar PPIMV and bias points for the power tubes.

I do have some things I want to include in the schematic, but I just don't know how and I hope I could get some feedback on it. I am talking about the following:
- Extra (switchable) gain stage like rj has done to his Rocket:
https://tubeamparchive.com/viewtopic.php?t=11401
- A high cut control, like in a K50.
- Are there any pro's or con's on using different diodes? Maybe UF5408 in the power supply?
- How can the bias circuit be adjusted to be able to bias in a wider range? Or is this not necessary? And in what range should R29 be?
- FX loop, yes or no?
- A 'slave out' jack for direct recording. With a line level pot.

These are the questions I have for now, but the list will probably get bigger as I go. I am sorry in advance for my long post and I hope I didn't make any rookie mistakes here. All feedback, tips, help or whatever is welcome!
Have a great day and take care.

[Gibsonman63]

Mulder,

Just my two cents:

The beauty of the Express is the simplicity of the design. I would not muck it up by adding a lot of features. Think of it as a life support system for the tubes, broken down to it's simplest form. There is plenty of gain on tap on this amp, I personally would not add another pre-amp section. The magic is all there, just get the right tubes and speakers and learn how to work the volume control on your guitar. There is an infinite variety of sounds in your volume control and playing attack.

Looking at the other end of the spectrum, I have worked on a few multi-channel mesa-boogie amps. With a million knobs and switches, I see guys struggling for hours trying to get a couple of good sounds from them.

It is hard to get a bad sound out of a properly working Express.

That being said, I have used can caps on my Liverpool build and would not hesitate to use them again on my next build.

[Clyde]

The cut control is a big improvement over the presence control, which I think has limited usefulness.

[M Fowler]

The cut control is a big improvement over the presence control, which I think has limited usefulness.

Yup I agree, add the cut control.

I also like Martin Manning's PCB/eyelet type Express in which we have Volume, T, M, B, presonace, treble cut and master volume.

Mark

[Mulder]

Thank you both for your replies. I know that the Express is an amp in its own category, but there are some features I would like to add to it. For example, the PPIMV and the slave out would be a great addition in my opinion.
Also, I wanted to create a layout that is capable of expansion, so that if I decide to add something, I don't need to make a whole new turret board.

How about the schematic I posted? No mistakes yet?

[Zippy]

I would really like to build an Express, but with a couple of additions. I have found different bits and pieces of information and ideas on this forum, but I am stuck at the implementation of them.

The Express is not known for being a friendly amp to a lot of changes. If you have never built one, you might concentrate on making a good one first, then making another after you know you can build one that is stable.

- Extra (switchable) gain stage like rj has done to his Rocket:
https://tubeamparchive.com/viewtopic.php?t=11401

The Express is an amazing balance of gain stages - adding another gain stage to the mix will just take it down the wrong path, IMNSHO.

- How can the bias circuit be adjusted to be able to bias in a wider range? Or is this not necessary? And in what range should R29 be?

When you make the range wider, you lose the ability to fine tune the voltage.

- FX loop, yes or no?
- A 'slave out' jack for direct recording. With a line level pot.

The Express is sensitive to lead dress. If you start adding more wire to the dress - especially if you have never built an Express that works well - you may well introduce instabilities that will have you chasing your tail.

[Mulder]

Thanks for your reply Zippy. I have decided to build a stock Express first, before I change anything. However, I don't like the stack of caps and I tried to design my own layout. My progress thus far can be seen in the attachment. I would like some feedback on it since this is the first time I designed a layout myself.
I have no idea how big certain components are, so the layout is far from finished. However, I am wondering if I am on the right track. Help is appreciated!

[M Fowler]

Yes what you are doing has been done before and gets rid of the cap stack.

Also I have had good results using can caps 50/50 and 40/20/20/20 JJ's.

[Mulder]

Thanks Fowler! I guess I will stick with the F&T caps and I want the whole circuit on one board, so the Hoffmann layout for example wouldn't work.
I will finish my layout and will try to find the correct dimensions of the components. But using one ground bus instead of using different star grounds isn't a bad idea?
And another thing, should the power supply caps be rated at 450V or 500V?
Thanks a lot!