STK0050 replacements for Pioneer SX-780 by/from Pyramid Audio?

[VAEngineer]

Hello-

New to the vintage receiver sx-780 test/repair arena.

Acquired an sx-780 with a shorted Darlington STK0050.

Was looking at the replacement stk0050 from this thread- and the parts list/ebay item
https://audiokarma.org/forums/index...lacement-for-sx-780-and-others.721181/page-44

and am not quite ready to test my very intermediate soldering skills on building them myself.

I noticed these units by Pyramid Audio of Austin Texas -
http://www.pyramid-audio.com/special.html

and I wonder if anyone has tried them out as a replacement for a blown STK0050? I emailed pyriamid audio and got a nice reply saying they would sell direct vs. ebay for a slight discount - and he had seen the open source version and the specs on his unit was simlar.

Not being a circuit board expert it looked quite different.

Anyway, thanks in advance. I will be posting soon about how to get my sx-780 running - as the relay does not click/make contact. I tested it with a dim bulb tester - and it was safe to power up and it lights up, fm stereo lights, etc. but no output, no click. thanks.

 

[merlynski]

The usual suspect (along with fragile STKs) is Q25 unsoldering itself over time with heating up and cooling down, reflow the solder on it, and the other TO-220s near it and try powering it up again.
In the Green/Purple Box:



Q25 is closest to the big heatsink.

Bottom view of a more obvious failure (in circles):

 

[VAEngineer]

thanks merlynski! Will check those. Could you tell me what you think of the Pyramid Audio stk0050 replacements?

https://www.ebay.com/itm/STK0050-re...263612?hash=item1ce783df7c:g:21cAAOSwCg9eijvw

 

[merlynski]

thanks merlynski! Will check those. Could you tell me what you think of the Pyramid Audio stk0050 replacements?

https://www.ebay.com/itm/STK0050-re...263612?hash=item1ce783df7c:g:21cAAOSwCg9eijvw

Since you asked me specifically, I go with the custom hbrown/rcs16 modules. I have used them personally, they work great, are easy to build and install. I do not have any opinion about the Pyramid Audio unit, but have not heard anything bad about Pyramid Audio.
The hbrown/rcs16 units are about 2/3 the price, but you do have to build them yourself.

 

[merlynski]

Oh yeah, Welcome to AK!

 

[slowhands951]

Since you asked me specifically, I go with the custom hbrown/rcs16 modules. I have used them personally, they work great, are easy to build and install. I do not have any opinion about the Pyramid Audio unit, but have not heard anything bad about Pyramid Audio.
The hbrown/rcs16 units are about 2/3 the price, but you do have to build them yourself.

Since Sanyo quit making STK 0050 hybrid modules years ago, you do have a problem with replacements. Of course, used pulled original Sanyo parts are one option. There are also cheap Chinese clones of the STK 0050 available on ebay and Amazon, but you don't know what you are buying. Some test out OK and seem reliable, while others use such cheap parts that they fail quickly. Counterfeit parts from China have been a disaster for me in the past, so they raise red flags for me. Check out horror stories on Youtube.

You can bite the bullet and spend a bit more on module kits built from readily available discrete parts, similar to the Hbrown/rcs16 assemblies discussed here. At this writing there are kits on eBay. They are not cheap, compared to a clone STK-0050 module (now a module clone costs, say, $13, while the module kit costs say $55). The kit modules work extremely well, and have several advantages. They have a bias current adjustment pot, which some amps do not have, and if they fail, you can replace any failed individual part fairly inexpensively. If you are on a tight repair budget, they don't make sense and you will have to take pot luck with a clone part. But if you can afford the upgrade, it will probably last longer and work better.

There is another option at slightly higher price, a more compact version from Pyramid Audio in Austin, Texas. It is available on ebay, assembled for about $65, and uses a different design implementation. It is assembled using surface mount parts and a different power Darlington transistor pair, one with a bias diode pair on each transistor die. This sounds technically superior, since the bias diode drop would closely track the Vbe of the two transistors on the same die, without the need for an external adjustment. Whether this is really a major advantage in practice I don't know, but it sounds like a great idea. Better tracking, no adjustment. I also like that the power transistors mount directly to the heat sink in the original module mounting holes, rather than using an extra aluminum plate.
chrome-extension://oemmndcbldboiebfnladdacbdfmadadm/https://www.onsemi.com/pub/collateral/and8196-d.pdf

Pyramid is making a wide range of Sanyo hybrid replacements for the repair trade. As these replacement parts become less and less available, it's good to have these other aftermarket options. https://www.pyramid-audio.com/modules.html

 

[painttoad]

If you are on a tight repair budget, they don't make sense and you will have to take pot luck with a clone part.

if one is on a tight budget then it makes more sense to put the unit on the shelf and save up for the good parts rather than piss it away on junk.

or sell the unit to someone that can and will do it right.

i'd go for rick's modules any day over the pyramids. rick's are easily repaired if needed.

 

[ConchBoy66]

Oh yeah, Welcome to AK!

Miss you!

 

[slowhands951]

if one is on a tight budget then it makes more sense to put the unit on the shelf and save up for the good parts rather than piss it away on junk.

or sell the unit to someone that can and will do it right.

i'd go for rick's modules any day over the pyramids. rick's are easily repaired if needed.

I mean no offense. Rick's modules are a known quantity, quite good. I'm not criticizing them. I simply pointed out other options. Let's have a spirited but respectful discussion on this problem.

Here is what I observe. Both Rick's STK 0050 and Pyramid's STK 0050 are expensive, about $130/pair. If that makes a repair over budget, I can find new modules for about $13 on eBay and Amazon from credible vendors with warranty. There is a risk they will be junk, but it's what's out there. Or you may prefer the original module. In that case a known good pulled part might serve, for a similar price. If budget is tight, that's what I might have to do. Sometimes in the real world the customer just wants it fixed fast, within budget. Economics decide the issue.

But if you would prefer to wait and get a better solution for more cost, I'm all for it. Do remember we're fixing up 45 year old consumer audio equipment, so spending a lot of money in just this area alone may not fully solve the problem. You may find you need to replace a lot of electrolytics, and a few ancient transistors, at the same time to get perceptible improvement. Just saying.

But if you want to upgrade, there are two options: "Rick's" type of module, or the Pyramid Audio modules. I've found only one supplier of "Ricks", assembled. They cost about the same as the Pyramid Audio STK 0050 -- Say $135 for two plus shipping and tax. The Pyramid pair costs $130 plus shipping and tax. Cost is about the same. Here are pointers to vendors, which may go away over time:

Unassembled kit, Version R:
https://www.ebay.com/itm/225869582726?itmmeta=01HVW8KD582H5TKEJ9490SGE4A&hash=item3496e05186:g:5aYAAOSwKpBiAtM8&itmprp=enc:AQAJAAAA0KyxiioJyeDX0vLj3wUtHPBWg0rdIi7U4i7sR2WSfjO2Lgo4Cizmr+EqfyQu6lHkZqMqZecc34HNJXFnPmayit65NKW+wqbYAy/K4ozNzd5bEkR/qLrSiktkQkMa+EpdVUO96sG7t/Ytz+zHTSr6TuBfy7UruQbZeTN80nmWInqzX7Rv6/6i7E7MhBh3daNWO5oZ4f6T9rT1likbqVtIl7hyfC7RDOApwRldQtC1ophWN4rUyh1tNRnzlVXcfWPH6mYkI30k4DZ/PsJ/sDZjaWo=|tkp:Bk9SR-jSzYjfYw

Assembled Version R:

Pardon Our Interruption...

Assembled Pyramid Audio version:

STK0050+ for Pioneer SX-780 or Marantz SR4000; replaces STK0050/30/40 | eBay

The STK0050+ fits these models and probably a lot more SX-780, SR4000, KR-5010, RS-2004A, JA-S44, JCX-2050. STK0050+.SX-780, SR4000, KR-5010, RS-2004A, JA-S44, JCX-2050. YES, every module tested in our Pioneer SX-780 or Marantz SR 4000.

www.ebay.com

Technically, I see these different implementations of the same 1970s-era module technology to be very similar in theory, with pro's and con's for each implementation. Rick's uses familiar parts, which can be replaced easily. So can the active parts in the Pyramid, using standard but less familiar Sanken or OnSemi parts that have been around for at least a decade. Instead of using two transistors per leg, Pyramid chose a Darlington single chip, with dual diode on chip to track the Vbe's of the two transistors. That is inherently more reliable, because it has fewer active chips (two vs five). The Vbe tracking will be more accurate, because they use the same fab process and are thermally coupled intimately.

Here are Youtube videos of real installations:
Version R install:

Version P install:

Just for fun, I'll pick up a beater SX 780 and try both module types. I'm curious how each sounds. Time will tell. I honestly don't know.

 

[painttoad]

I can find new modules for about $13 on eBay and Amazon from credible vendors with warranty.

that warranty is worth about $13!

if that knockoff goes up in smoke, it will not cover any other parts that it takes with it nor will it cover any labor.

i doubt the pyramid has a fraction of the support , if any, that rick's kits have.

Do remember we're fixing up 45 year old consumer audio equipment, so spending a lot of money in just this area alone may not fully solve the problem. You may find you need to replace a lot of electrolytics, and a few ancient transistors, at the same time

i know that and i refuse to work on a 780 unless all that is done at the same time.

fixing up 45 year old vintage audio is not something that should be nickel & dimed. do it right, pay to have it done right or pass it on to someone that will do it right.

i had a guy not long ago that kept hounding me to just put a bandaid on his 780 just to keep it limping along. i COULD have fixed the problem but how long before the next thing failed?(and it will) then i will have the same unit on my bench for another problem. i'm not into that. i don't ever want to see the same unit on my bench for any reason whether it's my fault or a cheapskate owner's fault. that's just how i am. i'm not a brick n mortar repair shop who's main goal is to get them out the door as fast and cheap as possible knowing that if it comes back for another reason, it's another bench/repair fee.

these things are not much different than vintage cars, restoring one is a labor of love and many times exceeds the value of the unit. the difference is that no one cheaps out on the motor of a vintage car nor do they leave the brakes original until they go out.

 

[zebulon1]

My thoughts in random order:
Im glad theres some competition and choices when selecting replacement options.
Rick and H Brown developed those modules for the community and made them open source. The cyphering through the process is a lesson in electronic project building. It’s a fantastic journey.
The frugal aspect shines through when following that path.
Rick even responds and provides kit support when asked through the post, whether bought or DIY. How cool is that?
I was selling the basic kit at cost when the modules were a new design. It was a chore keeping up. I was relieved when Rick took over. What he’s asking for the modules is extremely fair when considering the quality and support.
Any unit that those modules fit in sound fantastic when converted. It wakes up the piece like no other. Scientifically proven.
One other missed aspect of Ricks module is the hundreds of new AK members he brought to this forum, who stayed and contributed.
A guy would be missing something by leaving the working STKs in and not swapping them out for these modules.

 

[rcs16]

Fyi

The Sanken devices used in the pyramid products have been discontinued for over a year now.
As for our stk, as long as Toshiba and Onsemi sell the parts we’re good for the time being. Nothing like having second sourced parts.
Recently I evaluated the SPTech versions of mje15032/33 and njw3281/1302 and they performed just fine. They are more economical but are only available using the supplier LCSC