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Old 9th May 2012, 01:09 PM   #161
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okei. 55C is fine. but not any hotter
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Old 9th May 2012, 01:14 PM   #162
AndrewT is offline AndrewT  Scotland
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I have had a JLH running pretty hot for a few days.
The tips of the heatsink fins are above the "burning fingers within 5seconds" test temperature.

I would guess the output devices, 1pr mj15003 are running at Tc~80C and Ts~70C

So far I have not detected any deterioration in performance.
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Old 9th May 2012, 01:15 PM   #163
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I've got a couple of slow running 50mm fans which "waft" air throughout the body of the amp to keep the caps cool.

Inevitably they will pick up some heat from the MOS-FETs to keep the cat warm.
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Old 9th May 2012, 01:16 PM   #164
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Quote:
Originally Posted by AndrewT View Post
I have had a JLH running pretty hot for a few days.
The tips of the heatsink fins are above the "burning fingers within 5seconds" test temperature.

I would guess the output devices, 1pr mj15003 are running at Tc~80C and Ts~70C

So far I have not detected any deterioration in performance.
I opted to try to keep things a bit cooler for reliability reasons.

Have you tried some 12V fans running at say 5V. They are almost silent at that speed and make a huge difference to the efficiency of the heatsinks.
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Old 9th May 2012, 01:17 PM   #165
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Quote:
Originally Posted by AndrewT View Post
I have had a JLH running pretty hot for a few days.
The tips of the heatsink fins are above the "burning fingers within 5seconds" test temperature.

I would guess the output devices, 1pr mj15003 are running at Tc~80C and Ts~70C

So far I have not detected any deterioration in performance.
those fets can withstand more heat than a TO247 case.
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Old 9th May 2012, 01:22 PM   #166
AndrewT is offline AndrewT  Scotland
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This is still in the "experimental" stage.
I can easily lower rail voltages and/or bias to suit the sink.

Experimental, because the output offset wanders massively before settling down to a nice low value. I will probably change to an AC coupled version on single polarity supply to completely avoid the offset issue. The output cap can be both a DC block and bandwidth filter for mid or treble drivers.

Sorry, this is substantially off topic but some of the content can be extended to F5 operation/s.
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Old 9th May 2012, 01:24 PM   #167
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by AudioSan View Post
those fets can withstand more heat than a TO247 case.
Yes, the 200C spec is 25Cdegrees higher than most FETs.
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Old 9th May 2012, 01:27 PM   #168
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I listened to a stereo version of F5T V3 lastnight. There is something we are all missing about it that was in the original article. The presence of the gives more Class A bias for a given setting than a standard F5. I am not exactly sure of the theory, but it is plainly stated by Nelson. Last night a listened to Magnapans with just a single output pair, and I find myself surprised at the ability of this amp to drive anything.
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Old 9th May 2012, 01:31 PM   #169
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Quote:
Originally Posted by KatieandDad View Post
Has anyone had a successful F5(T)v3 build yet ?

I'm intrigued to see how much heat they are ditching.

I've got a DIY Aleph 4 which gets quite - but not excessivley - hot.

I'm wondering wether I can't use it as a donor for a dual mono build. ie keep the chassis, heatsinks and power supplies. +/- 48V may be too high even for the V3 ???
Myself and Buzzforb have a few iterations we are playing with, but I have not tried as a goal to push the heat. More to make sure the circuit is functional. It is, and that was my main goal.

There really have been no surprises, other than that the cascode set up takes some thought around biasing. So far we believe that higher IDSS JFETs in the V3 design makes it easier to get some range of bias out of the pots.

It sounds like you Aleph platform can handle the heat here, if not - just bias a bit lower.
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Old 9th May 2012, 01:31 PM   #170
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Buzzforb/ Tea Bag

I'm intrigued.

How would you review the F5T ??

Last edited by KatieandDad; 9th May 2012 at 01:38 PM.
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