Excellent, Very few DIY'ers end up with overkill heatsinks.... Sounds like you have room to crank up the bias then!
I had a great time yesterday at erpiii's place, and and very happy to report that he built an amazing pair of monoblocks. All they needed was a bit of courage to keep turning the pots and get everything to bias up properly.
The heatsinks are genuinely amazing overkill... With a drop of .55V across the .47r source resistors, a bias of 1.17A, the heatsinks were warmer than ambient by 12deg F!!! Yes, that's not a typo, and it was true for both amplifiers. It's disconcerting to have such a low heat rise. We let them cook for quite a long time and they just didn't get warmat all, but all the measurements showed they were flowing current and behaving properly.
This is an interesting case --- the first bias limit reached will be the (safe percentage) of the rated disipation of the transistors... They are not going to get particularly hot running even at 1.5-1.7A bias, so even more could be tried.
The irfp240 is a 150w device, with a linear derate of 1.2W/degC above 25. So if they are cranked up to 65C at the face (also pin 2) they would now have a max dissipation of 102W ( as there was a loss of 48W with the 40 degC rise in temp)
I would assume that for safe and reliable operation you really don't want to exceed 1/2 your rated dissipation, meaning 50ish watt. With 21.5V rails that would be a whopping 2.3A bias, or a drop of about 1.1V across the source resistors.
I would be curious to know what Nelson's opinion of running an F5 this hard would be. It seems like an awful lot to me, but I've never had an amp with that kind of heatsink capability.
The amps are very impressive looking in person, I hope a few more photos are posted.
The heatsinks are genuinely amazing overkill... With a drop of .55V across the .47r source resistors, a bias of 1.17A, the heatsinks were warmer than ambient by 12deg F!!! Yes, that's not a typo, and it was true for both amplifiers. It's disconcerting to have such a low heat rise.
We let them cook for quite a long time and they just didn't get warmat all, but all the measurements showed they were flowing current and behaving properly.This is an interesting case --- the first bias limit reached will be the (safe percentage) of the rated disipation of the transistors... They are not going to get particularly hot running even at 1.5-1.7A bias, so even more could be tried.
The irfp240 is a 150w device, with a linear derate of 1.2W/degC above 25. So if they are cranked up to 65C at the face (also pin 2) they would now have a max dissipation of 102W ( as there was a loss of 48W with the 40 degC rise in temp)
I would assume that for safe and reliable operation you really don't want to exceed 1/2 your rated dissipation, meaning 50ish watt. With 21.5V rails that would be a whopping 2.3A bias, or a drop of about 1.1V across the source resistors.
I would be curious to know what Nelson's opinion of running an F5 this hard would be. It seems like an awful lot to me, but I've never had an amp with that kind of heatsink capability.
The amps are very impressive looking in person, I hope a few more photos are posted.
There's a copper rectangle tube behind the heat sink that the rectifiers are mounted to, as well as the ground attachment. When I bought the heat sinks the price point for 10 was not much more than 8. It also helps a little with the cantilever of the torodial and PS board hanging off the other side. The rectangular tube is counter sunk into the sides and handles the torque weight of the torodial... the heat sink also covers the torodial from view and adds mass. A tit bit gaudy but the rectifiers will never get warm either. I plan on putting a magnetically attached glass on the fronts.
Im not going to be modding these anytime soon... they sound effortless with the B1 pre and I have a lot listening to do!
Congratulations. Yes, you have 3 years or so of listening to catch up on.
This certainly has turned out to be an all round good news thread
+1
What a remarkable thread indeed.
Here's what they look like. I'm using them with a B1 and a pair Of Zaph SR-71's that I cast out of concrete.http://www.diyaudio.com/forums/multi-way/167051-zaph-sr71-build-concrete.html#post2190479 They are replacing a pair of Peter Daniel's chip amps http://www.diyaudio.com/forums/audi...kit-building-instructions-97.html#post2036251
I think they are enjoying their new home, I know I am!
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The heatsinks are genuinely amazing overkill... With a drop of .55V across the .47r source resistors, a bias of 1.17A, the heatsinks were warmer than ambient by 12deg F!!! Yes, that's not a typo, and it was true for both amplifiers. It's disconcerting to have such a low heat rise.
6L6... I have raised the bias to .69V; 1.46A of bias. The heatsinks are running at around 88F, 21 deg F over ambient. They seem just a little warmer but not even close to hot. Between all the sinks there's just a warm updraft. Summer should net the same approximate ambient temperature due to all the the conditioned air heading down where the amps are. I think I'll keep the current bias in a holding pattern for a while; plenty of amp for my speakers in a small room!
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