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Old 22nd September 2009, 05:17 PM   #4951
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Quote:
Originally Posted by sangram View Post
Would you think the IRFP 540 and 9540 make acceptable substitutes for the output devices of the F5? Any candidates for the input pair if no SK/SJ available at all? I'm keen to see the differences from changing out the parts to something locally available for my second build (woofers).

On another note, I got the heatsinks, I hope there will be no problems with these ones - I should post photos in a few days. They have 1/2 inch thick bases and are 12x15x8", two should be enough for a stereo F5 hopefully - they weigh about 10lbs each
If you have a thermometer, a power resistor and a power supply you can measure their thermal impedance. Attach the power resistor to the heatsink, measure the ambient temperature, cook the resistor at a measured number of watts for 10 minutes or so (i.e. if it's a 50W, 100 ohm resistor, use your Ohms law to figure the required voltage), measure the temperature at the end. The temperature delta divided by the power gives you a pretty good approximation of the statistic sought. I use this method with all the dumpster heatsinks I've come across.

FWIW, the Yamaha A-10 integrate amp I modded used a heatsink made of aluminum flashing folded accordian style -- and it runs really well. The thermal impedance is Mostly (not entirely) related to surface area.

I am trying out the TO-220 Fairchild Semiconductor devices to replace the TO-247's.
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Old 22nd September 2009, 05:24 PM   #4952
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Originally Posted by Zen Mod View Post
CLC is always better than CRC
CLC is 3 poles.

Model 2 pole filters for equivalency.
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Old 22nd September 2009, 05:59 PM   #4953
sangram is offline sangram  India
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Thanks again Jack. I have some 10 ohm, 50 watt resistors and a thermal attachment for my multimeter, so maybe I'll do just that.

These heatsinks are meant for power rectifiers and I was told that 60 watts/20 degree rise would be a piece of cake for them, so I'm hoping for the best. They have a very thick and heavy base with two thick semi-circular ribs that extend from it, and the fins are then extruded from the ribs. It seems not as much surface area as a regular flatback heatsink, but much more mass.

It seems a lot of receivers come with the accordion-style heatsinks, my Pioneer receiver has the same thing, but with some sort of base press-fitted on to the flashing

I'll look forward to your results using the TO-220s. The only thing of note between the 540/9540 and 240/9240 (the originally specified devices) is the slightly slower rise and fall times, and the 100V rating instead of 200V. It really freaked me out to see a shop attendant here who looked at the Fairchild part numbers, deduced their ratings from the part number itself, and suggested the replacements (shops here usually have very dumb attendants). I bought four devices for about $3, if not in the F5 they can surely be used somewhere else...

I'd also love to hear of suitable candidates for the input pair, in case someone happens to try something else out.
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Old 22nd September 2009, 06:05 PM   #4954
ra7 is offline ra7  United States
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Jack,

Will the temperature delta (/Power) so measured be that of the total resistance from the resistor to ambient? It would include the thermal resistance of all the interfaces between the resistor and the ambient, and not just the heatsink to ambient.
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Old 22nd September 2009, 06:12 PM   #4955
sangram is offline sangram  India
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I'm assuming it will also include the internal thermal resistance of the resistor, which for a regular ceramic resistor will be pretty high. I plan to use a 30 watt soldering iron element. It will not be very precise, but it will tell me whether the heatsink will work or not...
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Old 22nd September 2009, 06:14 PM   #4956
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Originally Posted by ra7 View Post
Jack,

Will the temperature delta (/Power) so measured be that of the total resistance from the resistor to ambient? It would include the thermal resistance of all the interfaces between the resistor and the ambient, and not just the heatsink to ambient.
It's best to some silicone grease to the flat side of the resistor -- I use the finned Dale resistors for this -- so they are conducting to the heat sink and radiating into free air. The transistor will radiate as well (so do your IC's and voltage regulators) so you could use a 240/9240 as well and measuring the idle current and Vds etc. to arrive at the effective thermal impedance.
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Old 22nd September 2009, 06:57 PM   #4957
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally Posted by jackinnj View Post
CLC is 3 poles.

Model 2 pole filters for equivalency.
funny - L input filter is even better , sound wise
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Old 22nd September 2009, 07:29 PM   #4958
ra7 is offline ra7  United States
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You can actually determine it using heat transfer equations for finned heatsinks. Don't even need to measure it. But then you need a lil' engineering background.

Lemme see if I can dig this up.
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Old 23rd September 2009, 09:38 AM   #4959
sangram is offline sangram  India
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Thanks, ra7. It would help me skip a step.

It's a 'pi' shaped sink with the devices mounting to the flat side and fins along the two 'legs'. I searched for a similar profile through the Aavid site but could not find something to approximate the thermal performance.
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Old 24th September 2009, 12:29 PM   #4960
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Default block bridge vs MUR

has anyone compared bridge block vs MUR30x0
I use bridge block (KBPC3510) at now but got low rails - 21.8Vdc
I wonder how on semi ultrafast and softrecovery devices would perform
Is there something special about bridge mr Pass use In his F amps
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