DR: OT @ 2 Ohms/ 10" spkr Q.

[Chuck H]

Sorry. No pic just now. Camera is down (besides, my wife is out just now and she's the only one that knows the image upload software )

You can put it in a box or on a plate mounted to something else. So long as there is a mass of aluminum for extra heat sinking that will be exposed to free air. You may not actually need this since the resistors I suggested are rated in their own heat sink case, but screwing them to something thermally insulate, like wood, is probably bad. If you're just using cement type resistors just allow an inch between them and anything else and mount them in place with an aluminum plate pressing them into an aluminum case. That's actually how my personal unit is done.

Layout is utterly unimportant with the exception that you don't want this stuff near input or preamp circuitry (any more than you would want a speaker there).

Use heavy wire. Household cord is fine.

I've been using toggle switches. A standard AC mains "on/off" switch arranged DPDT will do. The idea of putting it on a footswitch is a good one though. If you were using the same tone for both lead and rhythm you could punch the "bypass" for a solo boost. Pretty fetched, but it's not a bad idea.

[Sea Chief]

Ok I think a std fat amp toggle switch is best idea. I see why yours is mounted on a sheet of aluM now, I didnt know there was going to be excessive heat involved. I need to use it both on the 5F1 to the DR hence I visualised the box & mono sockets.. but how Id get some sort of heatsink in there Im scratching my head. I want it small ideally as the Champ is a tiddler at W 11" x 13 high.

Would it be daft to be thinking thus: my compressor pedal box (a std small stomp box ~hammond mfg) would just squeeze in the Rheostat with mm's to spare (H) + two fat R's & switch. Just, but doable. The box is chunky thick aluminium.. so if I mounted the R's somehow onto the case floor-? or are we talking major heat involved?

[Sea Chief]

Damn.. box = trapped heat just re-read your #31. thats a no-go then. What I need is a 'n' shaped metal with edges to attatch or s'thing.. I still cant visualise a good design.

[Chuck H]

Yes, you need at least a little area on a surface or volume in an enclosure. I don't know what sort of resistors you're using. My diagram "implies" those alumnum cased resistors. But as I said, you can also use cement resistors if you give them some space. It's not rocket science, it's just heat. The heat is there because the watts need to go SOMEWHERE. A speaker turns watts into motion. A resistor turns them into heat. If you're clever enough to know that you need a pot holder when you take a tray out of a hot oven you can figure this out

This is (sort of) how I did a combo rear mount once on a bent plate of aluminum that I bought at the local hardware store. The aluminum doesn't need to be terribly thick since the bending and mounting adds considerable rigidity. The resistors are the aluminum housed, screw down type.

[Sea Chief]

Ok now I see a bit clearer Chuck thanks.. its just the metal black section thats going to be the tricky thing to source, then cut. I guess it neednt be more than a few inches wide.

Is a cement resistor same as a ceramic resistor > same as a wirewound resistor?

[Chuck H]

Ok now I see a bit clearer Chuck thanks.. its just the metal black section thats going to be the tricky thing to source, then cut. I guess it neednt be more than a few inches wide.

Is a cement resistor same as a ceramic resistor > same as a wirewound resistor?

I don't have any special metal forming tools. If I remember I just clamped the aluminum between two boards, wedged it up to the edge of a counter top and forced the bend. It came out straight.

You want wire wound resistors. "Cement" = ceramic. But the resistors with screw holes in their own heat sink simplify construction even if they are harder to source.

[Sea Chief]

Are these wirewounds the ones with two perpendicular lugs jutting out the underside?

Im going to have trouble finding any sort of steel or aluminium sheet for the job let alone cutting it. I just cant think of anything I could buy, or likely use, or salvage..

I think Im going to have to consider a box, but cutting even this Im going to struggle with and the excess heat inside.. I cant think straight at all with this job: ok the circuit is simple, the basic heat idea simple.. but in practise its far from straightforward to make.

[Sea Chief]

Are these the types you use, and are they designed to screw into anything in particular? 25W Arcol Aluminium Clad Wirewound Resistor 10R | eBay

[guitician]

The two holes are for mounting to your chassis, or heatsink.

[Sea Chief]

Hi yes I assumed they were for mounting, but whether they're specifically designed to screw to a heatsink was my Q (they look like they have a heatsink around them anyway).. or to put in quicker, ''do I have to buy 2 heatsinks for these types"?

[guitician]

If you look at this data sheet you can see that the added heatsink will give you added performance, but the dissipation for without a heatsink is listed too. Without a heatsink there is power de-rating. http://www.mouser.com/ds/2/32/Hs11-12.31-904.pdf

[Chuck H]

Are these the types you use, and are they designed to screw into anything in particular? 25W Arcol Aluminium Clad Wirewound Resistor 10R | eBay

That's them. Use the screw holes to attach them to an aluminum chassis of any sort (plate or box). I use a smear of thermal paste, but I don't think that's critical at all in this application.

[Sea Chief]

That's them. Use the screw holes to attach them to an aluminum chassis of any sort (plate or box). I use a smear of thermal paste, but I don't think that's critical at all in this application.

Ok Chuck I'll go for 2 of these then. Also ebay seems a possible source of some alu sheet.

Can you tell me what thickness is good for bending, just, so theres still some decent structure/ stiffness.. rather like your piece sounds ideal thickness (forgive me if I ~follow your idea here.. Im hopeless at imagining how such things might be done w'out an eg).

Thanks chaps.

[guitician]

1100 Aluminum soft sheet is the easiest to bend. I use .040" inch thickness. I bend it like Chuck said, against wood, or clamped between two pieces of wood.

[Chuck H]

What he said ^^^^^^^^^^^^^^^^^^^^^^^^^

It will seem a little flimsy in sheet form, but the bends and mounting sturdy it up just fine. Be sure to get a little extra so you can experiment with the first bend. That way you won't be out of business if something goes wrong. Not that it will. It didn't for me and I was just winging it. I do have a little experience though because I use to bend aluminum flashing into parabolic lamp reflectors. If you do have trouble I found that a shallow score in the aluminum helped create a nice straight bend.