Let's build a hopped-up Champ-ish thing

corliss1

Poster Extraordinaire
Gold Supporter
Joined
Sep 13, 2008
Posts
5,636
Location
Lansing, MI
HELLO EVERYONE!!! I haven't posted a good build thread in a while so I'd thought I'd share my latest lunchbox-style amp. The goals were:

-lower cost
-point-to-point
-avoid cabinet building
-usable volume options

I think what I came up with was pretty cool, so I'll show the full build process.

My last two build threads were:

-Mean 15 from 2015 - https://www.tdpri.com/threads/new-amp-build-from-design-to-flipping-the-switch.554230/
-Princeton head box thing from 2020 - https://www.tdpri.com/threads/lets-build-a-5f2a-princeton.1045092/

in order to make this small, portable, and avoid woodwork, I went with a steel Hammond chassis that has an enclosure available:

1.jpg


I made a plywood drill template that is color coded for different sized holes and some other helpful reference notes:

2.jpg


I clamp that down to the flipped-over chassis...

3.jpg


and then start drilling...

4.jpg


At this point there's really only two sizes, so I need to get the tube socket holes to 25/64" and the grommet holes to 1/2". I use 25/64" because the tube socket punches fit in a 3/8" hole, but that extra 64ths of slop makes getting out the punched metal much easier.

5.jpg


After making sure all the holes actually exist, I flip over my template to show the grinding template. This shows what holes need the powder coat removed in order to provide proper grounding to the chassis.:

6.jpg



A few seconds with an angle grinder and we end up with this:

7.jpg


Now we need to punch the tube socket holes. Let's grab the punches and get those mounted. Cutter on the outside so it doesn't leave any visible marks:

8.jpg


and the bracing piece on the inside:

9.jpg
 

corliss1

Poster Extraordinaire
Gold Supporter
Joined
Sep 13, 2008
Posts
5,636
Location
Lansing, MI
After a few turns of a the breaker bar, you end up with nice clean tube socket holes:

10.jpg


We need to mark the socket mounting holes:

11.jpg


There isn't much wiggle on these, so I actually hit it with a center punch to make sure the drill bit doesn't wander. See the little mark inside the circle drawn in marker?

12.jpg


After getting those drilled out, I need to drill and tap the enclosure mounting screws. I set the enclosure on the chassis and line it up nicely (everything is so dirty at this point...):

13.jpg


and then draw some more circles, punch some more centerpunch marks, and drill some holes:

14.png


Setup the 6-32 tap:

15.jpg


Tap it:

16.jpg


The bottom plate already has notches in it AND the bottom of the chassis already has holes that are ready to be tapped for 6-32 screws. How convenient of them:


17.jpg



So for this build I decided early on I wanted to use a plastic faceplate. Since it will have exposed edges, anyone using the amp would be at risk of very nasty cuts if the faceplate was metal. Plastic won't have this issue, but it is a bit more fragile during the drilling process. I'll do in multiple steps to ensure I don't crack the faceplate, as the drill bit can quickly grab the plastic and tear a chunk out rather than drill a smooth hole. Let's start by lining up the faceplate:

18.jpg


and then just make some starter holes in the chassis we can use later:

19.jpg
 

corliss1

Poster Extraordinaire
Gold Supporter
Joined
Sep 13, 2008
Posts
5,636
Location
Lansing, MI
I then go through and drill out all the holes to 3/8" as that's the standard size for both jacks and pot bushings:

20.jpg


The switch is usually 1/2" or just one size under. If you've ever drilled a hole for a pilot light, you know there isn't much wiggle room as that flange is SO TINY. I drill that hole to 5/8" and then hand file it to fit the pilot light bushing:

21.jpg


Now the part every builder hates - the IEC inlet. There are fancy punches that work well in aluminum, but they are several hundred dollars if you can even find the right size. I'm pretty good at doing these in aluminum, but it's much more work in steel. Here's the outline:

22.jpg


Drill out as much material as you can:

23.jpg


Then it's time to get the tools that are older than you and get to work:

24.jpg


Getting there........

25.png


There we go:

26.jpg


Let's add some mounting holes:

27.jpg


And she's all set now:

28.png
 

corliss1

Poster Extraordinaire
Gold Supporter
Joined
Sep 13, 2008
Posts
5,636
Location
Lansing, MI
To finish up the rear we need to mount our speaker plate. Just like the faceplate, we need to be gentle, so just some pilot holes to get started:

29.png



Then I get one hole drilled out to size:

30.jpg


I put in a jack to hold it in place:

31.png


And then use the round file from earlier to get the second hole finished. It only takes a few seconds to file that plastic to a nice shape:

32.jpg


I do the same with the front - get everything to a size where the file with fit through the holes:

33.jpg


Tape it in place:

34.jpg



Then file the holes to size:

35.jpg
 

corliss1

Poster Extraordinaire
Gold Supporter
Joined
Sep 13, 2008
Posts
5,636
Location
Lansing, MI
The last thing the chassis needs is to get all those metal burs cleaned up. We grab the deburring tool:

36.jpg


and just use that on every hole. That takes us from this:

37.jpg



to this:

38.jpg



See how much better those look?

40.jpg


Now everything is drilled, deburred, tapped, and reader to get some parts mounted:

39.jpg
 

King Fan

Poster Extraordinaire
Ad Free Member
Joined
Jan 1, 2013
Posts
8,184
Location
Salt Lake City
Thank you @corliss1 -- this is one of those rare build threads that combines crisp narration, useful tips, and great pictures, all in perfect proportion and with none of the yada yada.
 

King Fan

Poster Extraordinaire
Ad Free Member
Joined
Jan 1, 2013
Posts
8,184
Location
Salt Lake City
But I’d love to hear a bit more about the faceplate. Pro or DIY? If pro, how’d you make the template or vector art for them? If DIY, how'd you get it so nice? :)
 

King Fan

Poster Extraordinaire
Ad Free Member
Joined
Jan 1, 2013
Posts
8,184
Location
Salt Lake City
Aha, well, that works. And to think I was jealous of your tap and die set. :) Another tool question though. Noting your center punch, are you using a hand drill, or does the punch help with a drill press too?
 

corliss1

Poster Extraordinaire
Gold Supporter
Joined
Sep 13, 2008
Posts
5,636
Location
Lansing, MI
So let's get some stuff mounted in this guy. I ordered a bunch of these cool little terminal boards that come in 3, 5, 7, and 9 lengths:

1.jpg



but since they are riveted on you need to use spaces to raise them off the chassis:

2.jpg


For most areas I use these #8 x 1/4" nylon guys:

3.jpg


Here's what one looks like mounted up:

4.jpg


but for anything with a ground connection I just use a lock washer so I have good metal-to-metal contact everywhere:

5.jpg


I'm a huge fan of overkill, so it's nylon lock washers everywhere.

Let's get some of those boards mounted:

6.jpg


Add some tube sockets:

7.jpg


Here's where it gets interesting - we add power resistors that will be on both the 4ohm and 8ohm outputs so no matter what option you choose you'll have the choice of full power or 1/10th power. This is a modified version of the @robrob 10% Power Switch listed here: https://robrobinette.com/Generic_Tube_Amp_Mods.htm#10%_Power_Switch

8.jpg


I guess we also need some grommets in the big holes:

9.jpg


And then we'll mount the transformers. Full disclosure, this is my fifth build of this amp, and I'm doing this one for a friend, so I'm-reusing the transformers from my initial prototype. I think there's enough wire length everywhere, but I can always extend them if I need to. So if you notice the wires are weird already.......they are. Sorry Mike - good thing he'll never know because I'm totally not sending him a link to this thread...

10.jpg


I also mounted the IEC socket and rear plate/jacks. I'll leave the front plate and controls off until the power supply is wired, just so I can avoid scratching the faceplate. Besides that, the only thing left is solder.

It's going to be in this state for at least a few days while I work on some other projects, but there should only be a few more hours of work left before this is ready to fire up.
 




New Posts

Top