L'Amp: A simple SIT Amp

[OlavHaal]

Hi Michael!

Do you care to say if this is appropiate.

Nearly finished with my build - but have to travel to Scotland for a quick job(communication on Saipem7000). But I am waiting for a couple 1 ohm res - soon to come. Patient-patient.
But if my HeatSink for the SIT(found on E-bay) fail - I have spotted one that should fit in box and maybe in spec. On the Elfa-Distrelec- it is specd: Termisk resistans = 0.5 °C/W. Included is a picture of the HeatSink.

I have received a couple spare SK82 - so I`m safe if the first blow. And I didn`t know where to get the proper sink earlier.

So Michael - if you could help if my first SK82 goes up in smoke.

Best to all - and thanks for all support this far in my build.

Olav

[juanitox]

there is no reason to smoke them , i have made some wrong adjust with my variable source resistor , i 'v got near 4 amp with 19V with no problem. in fact with a source resistor it s impossible to kill it . good luck for your build

[dantwomey]

Originally Posted by dantwomey

Heatsinks Revisited. I'm wondering if the Wakefield 433K would work.
433K - WAKEFIELD SOLUTIONS - Heat Sink | Newark/element14 Canada

It seems to have similar thermal efficiency to the aforementioned Aavid D180-20.
D180-20 - AAVID THERMALLOY - HEAT SINK, T SLOTS | Newark/element14 Canada

Regards,
Dan

Looks Like surplussales has a good deal on the 486K. That's gotta be big enough!

486K - WAKEFIELD SOLUTIONS - Heat Sink | Newark/element14 Canada

[OlavHaal]

Hi Juanitox and thanks for positve remarks!

Yes - I think I will run them(mono-amps)with auto-bias always- AND soon order 2 - 100000 mF to mount across the source-resistor together w 10 mf polyprops.

So - the danger is bigger if you run without sourceresistor - lucky me who went for the autobias.

Today I tried the two 400watt Antek and they delivered accurately 35 Volt AC - which should give approximately 50 Volt DC.

Really looking forward to that moment - estimated time till my build is finished is 3-4 hours ++!

Best

Olav

[miklos]

Originally Posted by Michael Rothacher

I've forgotten who I promised this to, but here's the info on the Hammond 193V.

Not bad, and we get a nice efficency boost from the lower DCR iron core. You can put those 24V supplies to use now. I didn't experience any loss of inductance at 2A (or the rated 3A for that matter).

You could even run this one with a 20V supply @ 1.4A for a nice little 7W amp with 2% THD at full power.

No, I haven't listened to them. The measurements are in the pdf. Have fun.

Here is a similar version:
My first ever Class A amp.

[Michael Rothacher]

@Olav
.5C/W is good. The heatsink pictured looks reasonable by calibrated eyeball.

@dantwomey
The 486 is what I used in the original. It's plenty.

@All
The SITs are pretty robust current-wise, but running them too hot isn't a good idea long-term. In fact, the cooler the better, IMO. Remember, we're already pushing it on the Max Pd. I never hesitate to oversize my heat sinks a bit when possible. Also, do a really good job with the device mounting, clean the surfaces, and use generous amounts of goop. The heat will also affect the gate leakage and perhaps upset your bias. Thermal stuff is often ignored by us DIYers; the more amps you build, the more you'll pay attention to those matters.

[generg]

Originally Posted by juanitox

there is no reason to smoke them , i have made some wrong adjust with my variable source resistor , i 'v got near 4 amp with 19V with no problem. in fact with a source resistor it s impossible to kill it . good luck for your build

I second this!...... even without a source resistor and forgotten battery this SIT survived half an hour of good music at 3-4 A. It was my luck that the sinks were big.....!

At any case Good Work Sony!

[Variac]

I just got these on e-bay. My Hope Chest is filling!
175mm x125mm x 125mm

[ra7]

They look nice, Variac. Can they work with a TO-3 package?

[Michael Rothacher]

I have a pair of brackets made up that will fit those perfectly.

I used Arctic Silver between the bracket and heat sink and bolted it tight with 4X M5 hardware.