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Old 1st March 2009, 01:56 PM   #1
kenev is offline kenev  Greece
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Default Zen v.9 and heatsink temperature

First of all, I would like to say to Mr Pass a great "THANK YOU" for sharing all these years his knowledge and ideas with the DIY community.

After thinking about it for quite a long time, I decided to build the Zen v.9 to use it as a current (aka, transconductance) amplifier for driving my Fostex FE167 Voigt pipes. I was driving them with another tube transconductance amplifier, namely a design of John Swenson found in Audio Asylum. I was quite satisfied with this, but I wanted to try this Zen. I decided to build it in two monoblocks with 2 heatsinks for each monoblock, each measuring 160x200x40 mm and sharing the fets in the two heatsinks. After finishing the two monoblocks (actually not completed yet, just the full amplifier less the aluminum box), I listened to them and I was left with my mouth open from the first notes. The sound was amazingly fast, open, with excellent bass. In all, the best sound I have ever heard through my Fostexes.

So, it's now time to complete the mechanical part of it. Measuring the temperature of the heatsinks with an IR thermometer, I take readings of up to 58-59 degrees Celsius on the heatsink where Q3 and Q4 are mounted and around 53-54 degrees Celsius on the heatsink where Q1 and Q2 are mounted, with an ambient temperature of 21-22 degrees Celsius. The heatsinks I'm using have a nominal thermal resistance of 0.4K/W. My question is whether these temperatures are too high for the fets and whether I should use bigger heatsinks.

Regards,
Evangelos
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Old 1st March 2009, 06:41 PM   #2
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Those figures should be fine.

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Old 1st March 2009, 08:28 PM   #3
kenev is offline kenev  Greece
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Mr. Pass,

Thank you for your reply.

So, what is the limit of the heatsink temperature which is safe (without stressing) for the fets?

Regards,
Evangelos
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Old 2nd March 2009, 12:48 AM   #4
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My rule of thumb is fin temperature are 55 deg C. This is 60+
near the transistor.

You can run them hotter, I prefer not to.

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Old 2nd March 2009, 12:19 PM   #5
kenev is offline kenev  Greece
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I just checked again and found 45-53 deg C on the outer fins and 50-60 deg C near the transistors. That means that I am on the safe side.

Thank you once again.

Regards,
Evangelos
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