STK-0050 replacement for SX-780 and others

[zebulon1]

You might want to paste the aluminum HS to the chassis.
One thing I've been wanting to mention and I think its been said before.
The heatsinks should be dressed.
I use 100 grit and go to a finer paper to flatten the matting surface of the heatsink. Maybe to (220 or 320 depending on my stock). I'll use a table saw bed as the flat plate to fine tune the surface.
It doesn't take much to hone the aluminum down to a nice flat plane.

 

[Knutsul]

I flattend the alluminium HS but the HS from the reciever is not really that flat. So I was wondering if it isnt better to mount the transistors to the reciervers heatsink directly ? Or does the allu plate has a special purpose ? Still whaiting for the cooling paste they sent me the wrong one

 

[zebulon1]

I think you should keep the module intact .Aluminum HS and the whole deal. It would be some work to mount the module directly to the chassis.
Whats the big hurry?
Mount the completed modules, aluminum plate and all to the existing chassis where the original modules were located.
You might have to grind down a few through screws to get enough space to accommodate the modules.
If you wanted to assemble it and get it tested you could run it keeping an eye on the temps. Once the paste gets in - backtrack and apply the paste?
My two cents.

 

[Knutsul]

I agree that I should not rush! But maybe it is better to mount them directly to the heatsink.

 

[zebulon1]

What receiver are you working on?

 

[Knutsul]

sx-790

 

[rcs16]

I say to use the supplied plate, not worth the extra effort to drill tap the existing heatsink. It was done that way to make it easier.

 

[merlynski]

It is a lot of work to pull that heatsink to drill it, unless you don't mind risking getting aluminum shreds in the electronics circuits. Also if you don't want to grind down the screws for the heat spreaders inside the 'sink just put a washer or two under the screw heads. You can put some new grease under the spreaders at the same time.

 

[Knutsul]

Haha well then I wil use it, dont feel like in a position to be stuborn.

 

[Rational35]

We, as perfectionists, can agonize over best practice re: heatsink mating surface flatness and finish as much as we want.

It's good to take pride in a job well-executed.

That said, we're dealing with Pioneer SX780/790 and their ilk, not Phase Linear 700s, or multi-kilowatt switchers where R-Theta is critical. So making a heat spreader that satisfies our personal pride of workmanship, and mating it to the existing heatsink surface with a thin film of Wakefield 120 or equivalent will work a charm.

Don't sweat the small stuff. It's all small stuff. With apologies to David Lee Roth.

Merry Christmas to all.

 

[shortcircuit]

Thanks rcs16 and HBrown for this excellent upgrade! I was looking for something better than the STK0039 knockoff modules in my SX-680 and saw these on ebay. The sound is so much better now! The 680 has been running for over 72 hours and the heat sink is just warm to the touch.

 

[merlynski]

Thanks rcs16 and HBrown for this excellent upgrade! I was looking for something better than the STK0039 knockoff modules in my SX-680 and saw these on ebay. The sound is so much better now! The 680 has been running for over 72 hours and the heat sink is just warm to the touch.

Would you post a photo of the installed modules, please?

EDIT: clarification, in the SX-680

 

[tsd71]

 

[merlynski]

View attachment 1389879

Thanks, That is an SX-780, isn't it? I was hoping for a picture of the SX-680 that @shortcircuit put the modules in, to see how they are mounted and positioned.

 

[tsd71]

Thanks, That is an SX-780, isn't it? I was hoping for a picture of the SX-680 that @shortcircuit put the modules in, to see how they are mounted and positioned.

yup a 780

 

[Super Noob]

A little massaging, little drilling, and these things look like they where build for the RS 2010.

Need to figure out the proper way to bias and where to read... thinking 3 to 8.

RCS16... CCW all the in your BOM trimmer to start. Need to re-read this thread.

 

[Super Noob]

A little massaging, little drilling, and these things look like they where build for the RS 2010.

Need to figure out the proper way to bias and where to read... thinking 3 to 8.

RCS16... CCW all the in your BOM trimmer to start. Need to re-read this thread.

Maybe I should review your file.... the zip thing was throwing my rig off.

Here is the file by RCS16 (post 1)

https://drive.google.com/open?id=1H_MJzeUxPqVLoYzC1X2_46aEt3c2L5x5

 

[merlynski]

FWIW, On my modules minimum bias was full CW on the trimmer, turn CCW to increase bias. YMMV

 

[rcs16]

Your emitter resistors are 0.47 ohm, so with 40mA bias you want to set it for about 38mV across pin 3,8
I have the pot wired backwards, go figure

 

[Super Noob]

Your emitter resistors are 0.47 ohm, so with 40mA bias you want to set it for about 38mV across pin 3,8
I have the pot wired backwards, go figure

All right time get DBT, mini grabbers, and try to set bias around 40mV across both .47 resistors (7W). Will let you know how it goes.