2w Sub Miniature Express

[kineteks]

Well I'm out of parts & the snow is getting deep outside so it's time to quit, but....
what a cool little project!
It's a ball to assemble, about an hour or less in it so far & I'm slow....
....another Mouser order due in on Tuesday. I suppose I can work on the chassis

Thanks Dana, what a hoot!

[Structo]

Very cool project Dana.

I would like to get in on one of those later on.

Does anybody know how many db's these amps get to at the sweet spot?

[UR12]

Well I'm out of parts & the snow is getting deep outside so it's time to quit, but....
what a cool little project!
It's a ball to assemble, about an hour or less in it so far & I'm slow....
....another Mouser order due in on Tuesday. I suppose I can work on the chassis

Thanks Dana, what a hoot!

Looking Good!! I'll try and get the chassis drawing finished up tonight and post some measurements.

Very cool project Dana.

I would like to get in on one of those later on.

Does anybody know how many db's these amps get to at the sweet spot?

I will probably do more in a couple of months after we get any gremlins worked out of the build process. I have no idea how many Db these are but they sure sound louder than what I had imagined. It will be interesting to hear what some of the other builders have to say. I am also sure there will probably be a few individual mods before it's all said and done.

[kec]

Dana,

I know you're not busy but could you finish the BOM when you get some time? I need to get my order in to Mouser. I think the power supply and VVR are missing.

Have you thought anymore about the speakers? I just ordered a quad of Jensen MOD8's from music123. Right now, they have 15% off you entire order and free shipping over $49. I have no idea how these will sound, but the price was right.

[mcrracer]

This really looks great. Did I miss the schematic?, If I didn't could you please post one? Thanks

[Ron Worley]

I have built a pretty complete BOM, which I will release if Dana is OK with it. Mind you, there may be some errors and missing bits, but that's normal....

[UR12]

This really looks great. Did I miss the schematic?, If I didn't could you please post one? Thanks

The schematic is the same as the normal Express with only a few component value changes. The NFB resistor value was changed to 33k, the 150k in the gain stage was changed to 100k and the values of the tail resistors were changed to Liverpool values to keep from slamming the 5902s so hard. In the power supply the 220k resistor coming from the HV AC winding was changed to 68k because we are running about 190v B+ instead of 400v. But the rest of the amp is pretty much dead on in comparison to the revised Kelly schematic. Some of the components kept the same values but the wattages changed. Like the 25w 1k resistor became a 1K 7w or the 1k 5w screen resistors became 1k 1w. the 9.1k resistors in the power supply became 10k 1/2 w and instead of using two 9.1ks in series on the first node I used one 20k 1/2w resistor. The caps are all still polyester film, just smaller and rated at 250v, but they are still the same values as the original Express. The design is still evolving and I am sure that some of the first builders may have some suggestions for some changes as we go along.

[mcrracer]

Thanks for breaking it down so that even I can understand it.

[Ron Worley]

Well, Dana didn't comment, so here's a first go at a BOM for the 'Lil Devil....

As always, corrections are very welcome....

[mcrracer]

Question...On this BOM what schematic does the circuit designations refer to. I printed out the TW express from Kelly '90 schematic with UR12's revisions and it does not match up. Please help.

[Ron Worley]

Only Dana knows that, it's his design. And I think that it has some differences from the Kelly Schem...... as Dana explained in a previous post....

[Kregg]

Dana,
You've got to market these, your amp is an absolute thrill.

Sincerely,
Kregg

[UR12]

Question...On this BOM what schematic does the circuit designations refer to. I printed out the TW express from Kelly '90 schematic with UR12's revisions and it does not match up. Please help.

That is true. While the schematic is the same, the BOM part numbers for the Lil Devil match the PCB board and not the schematic designations. The board design software actually designated the part numbers when I designed the board. Of course the pin numbers on the tubes are different but there is still a cathode, control grid, plate and screens and suppressor grids on the pentodes. My goal is to make it easy as I could for someone who has the PCB to build the amp. If you're looking to build one of these from scratch then you will need to take the Revised Kelly schematic and come up with your own layout and BOM with the circuit changes I mentioned above.

[cap]

Big thumbs up on this project. Please count me in when you get started on the next batch of boards.

-cap

[kineteks]

...progress, cutting out the chassis is taking about 20X everything else!
...not a round hole on the front panel any more, rat-tail work for sure.
I've "adjusted" all the openings a bit more since these were taken and it's close enough to get the soldering iron out again. Still need to make spacers for the pots-to-front panel as they're working out to be a little staggered fore & aft.
I'm mounting the output jack in the chassis instead of on the PCB. The machined pin DIP sockets are sweet! ..they look cool too, I think.
...have to quit for the evening, can't wait to finish up...