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

[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]

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

[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

[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.

[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]

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]

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]

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.

[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?

[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]

Hi Chuck- it look a heavy duty beastie thats for sure. Ok so following your diagram I saved, I'll get a 1r 10w, a 10r 25w, a DPDT footswitch (is that the type of dpdt) and I guess two 11A Switchcraft mono jacks.

Would I need some heavy duty wire, maybe 1 of the 3 from a mains cable? (always seems a convenient quality wire at hand).

Im not quite visualising how the circuit actually physically would be- in a box? I think you mentioned your on a 'board' or something? do you have a pic you could show me?

Thanks, SC

[Chuck H]

Hi ChuckH (been away for a while/ got back to find Ohmite RJS25R on doormat).

Ok the RJS25R here.. measures 29 Ohms between lug 1, or lug 3 and the middle lug, dialing pot it ends at 4.5 Ohms.

Best make sure that seems normal?

gratefully SC

It's normal. You may get slightly different readings too if you jostle it in the fully rotated position at either end. Those things are pretty clunky, really. There may also be some flux or a harder than typical anti corrosive coating interfering that will wear with time. And because these things are USUALLY meant to attenuate power on big, course equipment, the terminals are made from a non audio grade copper that is tempered for toughness, higher in resistance, more likely to develop a fine oxide layer and pretty much welded rather than soldered. Don't worry about it.

[Sea Chief]

Wonder how you intend to do that .

Specially because 10V relative to 440V is *nothing*.

Ok understood JMF (Ive been away for a bit- thanks for your reply on 7th).. I spoke to a VG amp-maker personally who said 440v on a DR thesedays is nothing out of the ordinary, so I might try & get it down a bit later but for now Im sticking as is.

[Sea Chief]

For the 8 ohm unit you need a 25 ohm rheostat. For the amps you own you need at least a 25W rheostat but a higher wattage rating is fine. So, for your purposes, the RJS25R would be the choice.

Hi ChuckH (been away for a while/ got back to find Ohmite RJS25R on doormat).

Ok the RJS25R here.. measures 29 Ohms between lug 1, or lug 3 and the middle lug, dialing pot it ends at 4.5 Ohms.

Best make sure that seems normal?

gratefully SC

[olddawg]

I think thats a good idea Chuck. As its not complicated by all accounts, could you run me through your components.. maybe I could follow your plan if thats ok? would your 5F1 one be useable on a DR too or do they have to be similar wattagey like a 8w rheostat thing for a 5w 5f1, and a 25w type for a 20w DR? (hope to use with the DOM).

Ya know... I've done it both ways. I found out that after buying parts, enclosures, etc... Plus my time, it was more economical just to buy the Weber Mini Mass which sounds better and is more versatile. If you are not in the USA, the shipping might be prohibitive. But I would email them anyway, you might be surprised. They are very timely in their responses. What could it hurt?