[sachu]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif er? What I meant is, either you have a center tap to work with or you don't. When you do, use the lower current option (assuming you are willing to change the heater voltage when you roll in new tubes, perhaps that's what you're getting at).

Don't bother running the EHHA at 12.6 volts is what I am getting at. Just run them in parallel at 6.3 volts instead of series.

 

[luvdunhill]

Quote:

Originally Posted by sachu /img/forum/go_quote.gif Don't bother running the EHHA at 12.6 volts is what I am getting at. Just run them in parallel at 6.3 volts instead of series.

ahh... ok

I figured johnwmclean's was a more general question I guess. Carry on..

 

[jjazzyj]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif Gents, I am finally able to pay more attention to this thread. First, jjazzyj, I want to apologize for the previous post. Whoever put on the EHHA website that 2.5" heatsinks were adequate for speaker duty is an idiot. The best explanation I can offer is that I wasn't really paying attention. You guys have mostly sussed this out, however. At 18W into 4R each mosfet will burn about 18W itself. This is they typical effiency for class AB (mostly B) operating condition. If we can live with a 40C temp rise over a 25C ambient this will put us at 65C, ten degrees less than the halfway point to 150C. Now I know we won't have ambient but just to get a ballpark number this is 40C / 18W or about 2C/W. Given all the various thermal barriers between the junction and the air I think that Marc's recommendation that the heatsink itself needs to be 0.5C/W is a good one. And, of course, only off-board heatsinks can do this.

My calculation were for 8ohm drivers, and even then it was really close. So the recommendation for .5C/W is definitely required. Thanks.

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif how do you plan to attach the devices to the heat sink, via angle bracket? That's how I'd do it... Don't forget to add that in. But really, the fin orientation is the big hurt with those... Now, how can you measure the thermal resistance? I'd tell you, but it was a scarring experience that started when I got in between my wife and the oven in the kitchen

Via Aluminum Angle, yes. And I would have to guess at the thermal resistance on that as well. Grease between the two as well. The fin density on those heatsinks isn't that great, they are a big honkin' piece of aluminum however. And I'd have no idea how to measure the terminal resistance on that bad boy. And the shape doesn't lend itself to chassis manufacture very well.

What do you think of this heatsink?

NEW HEATSINK ALUMINUM EXTRUSION LARGE 7.29" WIDE on eBay.ca (item 170397104041 end time 27-Oct-09 17:23:14 EDT)

The shipping from Australia(Conrad) seems like it would be a killer.

I'd cut the heatsink into 4" length with the fins upright so that I'd have 2 EHHA channels(Balanced) on both sides, each with their own heatsink. It is very similar to the Conrad MF-20-100 which is .47C/W.

 

[jjazzyj]

This is probably another nub question as I know you really should try to avoid this...

When air wiring the mosfets you should solder the gate resistor directly to the pin? Is this correct? To prevent oscillation. I hope I read that right.

 

[runeight]

That certainly would work. You say shipping from Oz. Is there no US manufacturer for something like this?

As an aside, how is it working as a speaker amp. I don't think anyone else has yet done this unless maybe Ferrari.

 

[runeight]

Quote:

Originally Posted by jjazzyj /img/forum/go_quote.gif This is probably another nub question as I know you really should try to avoid this... When air wiring the mosfets you should solder the gate resistor directly to the pin? Is this correct? To prevent oscillation. I hope I read that right.

Yes.

 

[jjazzyj]

Quote:

Originally Posted by runeight /img/forum/go_quote.gif That certainly would work. You say shipping from Oz. Is there no US manufacturer for something like this? As an aside, how is it working as a speaker amp. I don't think anyone else has yet done this unless maybe Ferrari.

I mentioned Australia because of the previous mention of Conrad Heatsinks. The ebay link is an American seller with a 25$ flat rate shipping fee to Canada.

I can't find any other heatsinks like that around here.

This is mostly going to be used as balanced/dual headphone amp, with occasional speaker use. I'm excited about getting it to work. SOHA II was too easy

 

[luvdunhill]

Quote:

Originally Posted by jjazzyj /img/forum/go_quote.gif I'd cut the heatsink into 4" length with the fins upright so that I'd have 2 EHHA channels(Balanced) on both sides, each with their own heatsink. It is very similar to the Conrad MF-20-100 which is .47C/W.

yup, the heatsinkusa stuff would work well. In case you'd prefer to order outside of Ebay, here's a link to their website:

HeatsinkUSA, llc

Since the boards don't seem conducive to using angle brackets, why not mount the board on the heat sink itself, then mount the devices in the following "bottom mount" configuration:

It looks like the hole on the board could be enlarged in order to fit a screwdriver through in order to secure the device... make sense?

 

[jjazzyj]

Quote:

Originally Posted by luvdunhill /img/forum/go_quote.gif yup, the heatsinkusa stuff would work well. In case you'd prefer to order outside of Ebay, here's a link to their website: HeatsinkUSA, llc Since the boards don't seem conducive to using angle brackets, why not mount the board on the heat sink itself, then mount the devices in the following "bottom mount" configuration: It looks like the hole on the board could be enlarged in order to fit a screwdriver through in order to secure the device... make sense?

Thanks for the website address. I've been thinking about your mounting idea in combination with chassis configuration. I was hoping to expose the tubes for the 'coolness' factor. Though with a perforated top you could still see them I suppose The tubes would be horizontal inside the chassis with the heatsinks on the side. On the upside a simple vented top could be used and then the amp could be stacked a lot easier.

Thanks for the ideas. I think that I will forgo the coolness factor for practicality this time.

 

[Dougie085]

That guy on ebay's heatsinks are fantastic, I've ordered several before.

 

[johnwmclean]

I have my kits coming from GJA early next week

I’m planning something very special, monoblocks

There will be a total of 4 enclosures, 2 of them for sigma22’s and the other 2 for balanced EHHA amps. This of course means 2 IEC’s sockets and 2 stereo attenuators as well as umbilicals, not to mention relays and heater psu’s for each monoblock.

 

[sachu]

ooh...waay too complicated a setup for something that isn't as sensitive to noise pickup as a B22...but yeah..whatever works for you.

 

[nattonrice]

Quote:

Originally Posted by johnwmclean /img/forum/go_quote.gif I’m planning something very special, monoblocks There will be a total of 4 enclosures, 2 of them for sigma22’s and the other 2 for balanced EHHA amps.

Dear God O.O

At the next meet we'll need a third person to get back to your car =P

 

[johnwmclean]

Quote:

Originally Posted by sachu /img/forum/go_quote.gif ooh...waay too complicated a setup for something that isn't as sensitive to noise pickup as a B22...but yeah..whatever works for you.

I know this is despicable overkill

Quote:

Originally Posted by nattonrice /img/forum/go_quote.gif Dear God O.O At the next meet we'll need a third person to get back to your car =P

hehehe, “where gonna need a bigger boat”

 

[sachu]

Oh wait...you mean two balanced EHHA confgured as mono block speaker amps?

Yeah then the idea works fine....sweet..looking forward to this one.