STK-0050 replacement for SX-780 and others

[Rubber Ducky]

HBrown, you are absolutely right. And I deeply appreciate you and rcs16 going out of your way to provide this info to the community. Without you and the other experts here willing to share their knowledge, I'm sure many of us wouldn't even be in the vintage hobby.

The trouble for me is, I have exactly zero experience with pcbs or electronic componentry aside from an occasional simple soldering/desoldering of a single component, which I've done maybe 3 or 4 times in my life. I don't need any instruction for that, but building something like this is beyond my ability. I've downloaded the zip file but the only file I can open is the pdf, which has some pcb info in it but I have no idea what to do with it. I can barely read a schematic and I don't have the tools or the knowledge to build a pcb. The other files have extensions I can't open, but I'm sure I wouldn't know what to do with them anyway. If you gave me the ready-made circuit board and a detailed step-by-step instruction sheet describing how and where to solder each component and where/how to mount the board in the chassis, I could order the BOM components and probably do this successfully. It would have to be like buying a Velleman kit suitable for newbies. But I assume that's not going to happen, which leaves me with 3 options:

1. Pay one of you experts to build two of these modules for me.
2. Roll the dice with the knockoff STKs being sold on ebay.
3. Sell the unit for parts and buy something else that doesn't use STKs.

Since #2 is easy and the only cheap option, I'd be inclined to try that first. That's why I'm curious about the 80's. Or 60's. Or any Darlington STK that has a chance of working.

 

[rcs16]

The other files have extensions I can't open, but I'm sure I wouldn't know what to do with them anyway.

You are not required to open the files in the zip other than the pdf documents.

I made up this design so that you do not have to

2. Roll the dice with the knockoff STKs being sold on ebay.
3. Sell the unit for parts and buy something else that doesn't use STKs.

HBrown can possibly make the AL plates for you, at a cost. Zeb is also trying to get them made in a shop. Zeb could probably sell you a few of his pcbs, if he has any left, so you do not even need to order them yourselves. Soldering one up is a rather easy task. It is a high school level project. If you have questions, ask, that is what this thread is for.
I think the documents and the contents of this thread make the project self explanatory.

 

[sregor]

Attached equivalent electrical diagrams for STK output modules. A good tech or someone with some circuit theory should be able to figure out which ones will work, and how well (but no physical dimensions. ) Comment - a lot of pins are not connected, so it can make things easier (or harder) YMMV

 

[zebulon1]

My brother-in- law made a few in the shop, making sure the dimensions are correct.
The next set will be water jet made.
We are trying to keep the costs below $15.00 for the pair. Including the shipping and hardware. We think it can be done.
Rick and "HBrown" have made this project an open source and we want to follow suit.
This heatsink will make it easier to decide on which way to go when replacing the modules.

A little update:

 

[ILikePioneer]

does anyone have an updated BOM, some of the parts are no longer available

 

[merlynski]

I just received a shipment from Mouser with all the electronic components, except driver and output transistors,
I got the driver and output transistors from Arrow.com , (a couple are subs from the BOM):

MJE15031G
ON SEMICONDUCTOR
Price: $0.9544

NJW0281G
ON SEMICONDUCTOR
Price: $1.6715

MJE15030G
ON SEMICONDUCTOR
Price: $0.8911

NJW0302G
ON SEMICONDUCTOR
Price: $1.3787


No affiliation with Mouser or Arrow.

EDIT: As of 5/4 a couple of these are now backordered from Arrow.

 

[rcs16]

Someone I gave access too the Mouser BOM changed the quantities. I have rejected the edits, so it is back to normal again.
If I give you edit access to the Mouser BOM, (so you can see the notes) please do not alter it, if you want to change/delete/add, place an order based on the BOM listing and then make your changes to your order, thx.
If you suggest changes, let me know and I will review to determine if they are acceptable for changing the BOM.
As of today, no parts in the BOM are obsolete, some of the Onsemi bjts are on back order at Mouser.
As shown above, thx "merylnski" you can get these parts at other disti's such as Digi-Key, Arrow, Newark etc. Do not buy these parts from auction sites, not worth the chance. If I have time I can also put the BOM up on Digi-Key as well. I will update this thread if I do so.

Cheers
Rick

 

[jspernc]

Thanks for all the work which went into this project. I have built a couple of the amps and they work beautifully in my 780. Nice not to have to buy those cheap chinese knockoffs.

 

[zebulon1]

I finished the two modules this morning.
It took a little less than two hours to assemble both and each cost $27.00 in components.
The plan is to install them in a SX-780.

 

[rcs16]

Great to see folks using these modules.
Looks good, Zeb, I see you went with the side mount pot Hope it tests out fine.

 

[zebulon1]

That's what I had on hand. The multi-turn trimmer might be over-kill but the top access will help in the set-up.
Much Thanks, Rick and HB for the nice work-a-round.

I contacted Rod a told him to go ahead with a batch of heatsinks.

 

[Jeff Harrell]

Any chance of a youtube video of the assembly? I've ordered some stks from eBay and after a week they still work great. If they do fail, id like to do this

 

[zebulon1]

Finished the install in the 780.
Very nice!
DC Balance is virtually zero.
Idles are set at 7mV's across one emitter. Heatsink is cool to the touch at a moderate volume.
Runs cool and sounds really, really good.
You guys know I'm a big fan of the high power sets but this 780 with the module work-a-round is sweet.
First time this set ran in a very long time.

Notes:
On the 780 you have to build the module so it has no deck height. The bottom cover leaves little room for the module.
You will have to cut off the heatsink stiffener screw extensions allowing the module's heatsink to mate to the set's heatsink. I used a Dremel cut-off wheel.

All in all. A very nice project with high rewards. Total time spent building and installing both modules. 3.5 hours

 

[markthefixer]

Very nice work Zeb (cheese, you've been doing a lot of that lately!!), and one less project on my back burner - I couldn't be happier!!

 

[zebulon1]

Mark,
You got many of us interested in this hobby.
I for one, thank you for that!
Lightning the load is the least I can do.

 

[larryderouin]

Yeah, what ZEB said. Mark, you are an enabler, a teacher, and I consider you a good friend among a lot of friends here on AK. And I'm still learning from you every time you post. Sheeesh, I think it was back in 2008-2009 I saw the 1st reference of you saying "someone should do this". Keep beating your head against the softer drywall. Eventually someone will come up with it. And your head won't hurt as much.

 

[markthefixer]

Right: LOL, You can tell right away when you hit the wall with your head if you're up against springy drywall that makes a satisfying boom
or quieter plaster that makes you see stars. (tip: DON'T hit the plaster again.)

Those pictures Zeb? They just LOOK so RIGHT!!!

 

[HBrown]

Nice job Zeb- modules look great! On the 780, they do come pretty close to the bottom cover. I've found that the heatsink plates do not have to be as thick as my first ones were. Once I got my fastener lengths figured out, I began making the plates from 3/16" and even 10 GA aluminum. Even when biased fairly aggressively, I have not had any thermal problems. But, to couch that statement, I have not hooked it up to speakers that can absorb the full output and really cranked it for long periods.

I've gotten that nice, solid sound from everything I have put them in so far. Do you have the equipment to test the actual numbers on the finished set-up?

 

[zebulon1]

I had the 780 connected to a set of 8 ohm speakers just after the set came alive. Running it for over an hour at a moderate volume it barely got warm.
I thought the 3/16 plate would be a better/cheaper alternative to the quarter inch plate for the heat transfer as well as keeping enough threads to allow for the hardware..
The module will be attached to the original heatsink anyway so why the thick plate?
The idea of the plate makes for an easy install to the set, also as a nice platform to build the module. When assembling it I half thought to mount it directly to the sets HS but thought otherwise for the easy install reason.
Mounting it directly would require drilling holes in the sets original HS and hardware of either sheet metal screws or nuts, bolts and lock washers. It would create a mess of work.

I do have equipment and will test here in a week or two for my own curiosity. But really, this work-a-round works and sounds great.

Rod is finalizing the plate quote and we had discussed the plate thickness. I'm glad you (HB) mentioned this in your above post.

 

[rcs16]

The module will be attached to the original heatsink anyway so why the thick plate?

The Al plate was spec'd so that it matched the thickness of the original STK module and you could re-use the existing screws that are used to mount it and not have to

You will have to cut off the heatsink stiffener screw extensions allowing the module's heatsink to mate to the set's heatsink. I used a Dremel cut-off wheel.