Aleph J illustrated build guide

[roger57]

AL Oxide Pads

Has anyone tried the aluminum oxide pads from Aavid-Thermalloy? According to an app note I have from Motorola, they are superior to anything else (except beryllium), thickness accounted for.

However, this was written before Keratherm came across the ocean...

 

[BobEllis]

I tried them on a test rig, seemed to be around 1°C/W with a light smear of grease, IIRC. Measurement was with a contact thermometer on drain tab and sink.

Hmm, I will have to dig them out for my AJ build.

 

[jacco vermeulen]

aluminum oxide pads from Aavid-Thermalloy?

Keratherm 86/82 is way better than AlO2, twice better.
(Beryllium Oxide is toxic and difficult to obtain)

http://www.diyaudio.com/forums/solid-state/31077-krell-ksa-50-pcb-99.html#post777532

 

[roger57]

Keratherm 86/82 is way better than AlO2, twice better.
(Beryllium Oxide is toxic and difficult to obtain)

http://www.diyaudio.com/forums/solid-state/31077-krell-ksa-50-pcb-99.html#post777532

Not surprising...as said, that app note was out before Keratherm. Nonetheless, I will try both and see what the heat sink says, just for the sake of posting a comparison table.

I'm also trying to decode the thermal resistance numbers from heatsinkusa's website. They are saying for P/N "4.600" Wide Extruded Aluminum Heatsink", it's 1.4 C/W/3" . That should be 3" length...? So for a length of 9", thermal resistance should be 1.4/3 = 0.47C/W for the 8" piece.

Look right?

 

[Zen Mod]

not linear

 

[BobEllis]

It works out to be about .7 for doubling in length. So 1°C/W/3" would be .7C/W at 6"

Aavid had a calculator on its website if you are using one of the common profiles. for example http://www.aavid.com/products/extrusion-heatsinks/65535

Note that it also depends on the delta T between sink and ambient. Aavid shows this on their pages. Helpful.

 

[6L6]

Because it's 400 VA? Or because PSU voltage doesn't matter that much?/

The 400VA is much bigger than necessary - the Firstwatt factory built use 300VA... And as almost everybody uses 35V caps, the extra volts mean little.

What does happen when I'd increase PSU voltage?
Will the AJ be able to deliver (slightly) more power?

Yes, a little. Enough to measure, but not really enough to hear.

Bob Ellis got it correct - buy it because it's in stock. There is no downside.

 

[roger57]

It works out to be about .7 for doubling in length. So 1°C/W/3" would be .7C/W at 6"

Aavid had a calculator on its website if you are using one of the common profiles. for example Thermal Engineering and Heat Sink Manufacturing - Online Store

Note that it also depends on the delta T between sink and ambient. Aavid shows this on their pages. Helpful.

The link you sent was very useful. As ZM pointed out, and after some refresher reading on thermal transfer, indeed a non-linear relationship. Thanks!
(u2, ZM)

 

[gadut]

What is minimum voltage of C4 10uF? Is it the same as zener voltage 9.1V?

 

[Zen Mod]

yup

 

[KevinTams]

In my local suppliers Bc550 and ZTX 450 are both out of stock !! They have BC547B, the only difference is min hfe is 200 for the BC547 and 110 for the BC550. Will thiss matter?

 

[Zen Mod]

nope

just go for it

observe pinout difference between BC and ZTX

 

[KevinTams]

nope

just go for it

observe pinout difference between BC and ZTX

Thanks

 

[gadut]

yup

That's great. What about minimum voltage on C2 & C3 220uF? Would 16V be enough?

 

[Zen Mod]

schematic in first post of thread is bloody small

show me proper one and I'll see

 

[didiet78]

The schematic

 

[Zen Mod]

C2 35V
C3 16V

 

[gadut]

Thanks ZM, you are the Guru

 

[Zen Mod]

......... just in Da Pub

Guru of Dodossness

 

[stajo]

The Doodoo Gurus