SX 1250 FROM SCRATCH

[merlynski]

My observations are 4 to 8mA current through the STV in Pioneers (that is not a hard & fast number). An STV4 has 4 junctions in it, and it seems like the STV junctions run on the low voltage side, so I would expect about 2vdc. That leaves 7v to drop across the resistor. 7V/8mA = 878Ω. I would pick 1kΩ. The exact voltage is not critical because the VR adjusts the voltage setting of the bias spreader. If it is much lower or much higher, compare your reading to a different STV4. Seems to me I recall them being about 1.8 to 2.2v in functioning units. Others here may have different opinions. If so I would like to know, and learn from it!

 

[rhodus]

My observations are 4 to 8mA current through the STV in Pioneers (that is not a hard & fast number). An STV4 has 4 junctions in it, and it seems like the STV junctions run on the low voltage side, so I would expect about 2vdc. That leaves 7v to drop across the resistor. 7V/8mA = 878Ω. I would pick 1kΩ. The exact voltage is not critical because the VR adjusts the voltage setting of the bias spreader. If it is much lower or much higher, compare your reading to a different STV4. Seems to me I recall them being about 1.8 to 2.2v in functioning units. Others here may have different opinions. If so I would like to know, and learn from it!

Thank you...

 

[rhodus]

I have decided to pass this project along to another AK member. As events happened, it seemed to be a win-win move. He had the need, along with the expertise and equipment, to finish it up nicely while I have several non-audio projects that need my attention. A new house/shop with sound room being high on the list.....Thanks everyone!

 

[zebulon1]

I was the guy who bought this receiver from “rhodus” back in 2021.
I needed it for a tuner board and a few other parts and it seemed like a logical solution to my 1250 dilemmas. The tuner replaced a QRX tuner board someone horsed into a local customers 1250. There’s a thread on that somewhere in 2021. Sadly the owner of that minty 1250 is no longer with us. Not sure where the receiver is. Probably with the family. That 1250 was nice. I ended up doing the Full Monty on it.
Since then Ive been accumulating parts for it. Cleaning up some loose ends Craig left and rewiring everything except the rear component boards. He had the amps up and running. Nice work! If you have time, check out this thread. Enjoyable read.
Along the way, I robbed the 2SK30 FETs and found the replacement SMD 2SK209G’s from a couple that sells them mounted to a PCB. They have their own website where you can order as many as you want. Sounds like wifey does the soldering. Affordable and for a great cause.
These boards were bought as donors so they are not connected to the harnesses. I normally rebuild with everything connected.

 

[rhodus]

I was the guy who bought this receiver from “rhodus” back in 2021.
I needed it for a tuner board and a few other parts and it seemed like a logical solution to my 1250 dilemmas. The tuner replaced a QRX tuner board someone horsed into a local customers 1250. There’s a thread on that somewhere in 2021. Sadly the owner of that minty 1250 is no longer with us. Not sure where the receiver is. Probably with the family. That 1250 was nice. I ended up doing the Full Monty on it.
Since then Ive been accumulating parts for it. Cleaning up some loose ends Craig left and rewiring everything except the rear component boards. He had the amps up and running. Nice work! If you have time, check out this thread. Enjoyable read.
Along the way, I robbed the 2SK30 FETs and found the replacement SMD 2SK209G’s from a couple that sells them mounted to a PCB. They have their own website where you can order as many as you want. Sounds like wifey does the soldering. Affordable and for a great cause.
These boards were bought as donors so they are not connected to the harnesses. I normally rebuild with everything connected.

View attachment 3807901

View attachment 3807903

View attachment 3807928

Wow. I had forgot about this thread. Seems like another World ago now. Thanks for bringing it back up!

 

[zebulon1]

I’m working consistently on it. Afternoons, on the dining room table. The shop is 111 degrees after lunch so I head inside and work the electronics. A mini split is on the way.

 

[rcs16]

Makes wonder why they do not build houses with basements in Las Vegas?

 

[zebulon1]

Makes wonder why they do not build houses with basements in Las Vegas?

One word, mainly. "Caliche". It can drive up a pool cost to where it doesn't make sense or limits the scope of the project.
But the surface is extremely stable (Mostly rock with a sand binder) and no freezing temperatures. No reason to have deep footings. One underground contractor I knew, dug out a basement for his new house. It was a novelty. I heard tell they have used small charges of dynamite for the prep work, to make some progress through the hardened rock.

 

[rcs16]

Thanks, learnt something today
So I assume most have above ground pools because of the expense to dig one out?

 

[zebulon1]

Thanks, learnt something today
So I assume most have above ground pools because of the expense to dig one out?

No, mostly in ground, depends on the neighborhoods (HOA). The caliche runs in vanes and can be close to the surface or deeper in the ground. It's always a concern when wanting a pool.
Hey, I was reading a 2022 post you had on replacement 1250 drivers. You don't happen to know the component numbers off the top?

 

[rcs16]

MJE15032G, MJE15033G as drivers
KSA1381(KTA1381Y), KSC3503(KTC3503Y) for pre-drivers, vbe multiplier, VAS, CCS
KSA992 for input diff pairs, match Vbe to within 1-2mV as read on the DMM in diode test mode. use lead clips

 

[rhodus]

One word, mainly. "Caliche". It can drive up a pool cost to where it doesn't make sense or limits the scope of the project.
But the surface is extremely stable (Mostly rock with a sand binder) and no freezing temperatures. No reason to have deep footings. One underground contractor I knew, dug out a basement for his new house. It was a novelty. I heard tell they have used small charges of dynamite for the prep work, to make some progress through the hardened rock.

I've done my share of underground Electrical through Caliche in West Texas. Its no Picnic.

 

[zebulon1]

This is going to be a big job.
It took me an hour to make one shielded cable and wire it. There’s 16 to do.
I think it was MTF who said he worked on a set that had all the same color wires. I keep thinking of that as I make these cables.

 

[rcs16]

Lots of wire markers, take your time.

 

[zebulon1]

I’m using colored heat shrink at the ends.

 

[tarior]

This is going to be a big job.
It took me an hour to make one shielded cable and wire it. There’s 16 to do.
I think it was MTF who said he worked on a set that had all the same color wires. I keep thinking of that as I make these cables.

When I rebuilt this basket case DC300, I used Mogami 2947 for the signal wires. They come as a siamesed pair, which I separated.

Thread 'Marantz 300DC Basket Case'

Mar 14, 2025

Here is a basket case Marantz 300DC amp that someone gave me years (decades?) ago because they couldn't make it work. Almost all of the wiring and connectors in it were corroded and/or broken, along with a lot of the components on the driver boards and the meter/protection board were also corroded. I rewired it and replaced all the connectors with new Molex connectors. I don't even want to talk about how long this took.
What I started with. I repainted the worst part of the chassis that was all rusty. I bought some stuff on ebay, like the rear panel.

What was left of the...

• tarior
• Replies: 16
• Forum: Marantz Audio

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[zebulon1]

When I rebuilt this basket case DC300, I used Mogami 2947 for the signal wires. They come as a siamesed pair, which I separated.

Through your post I found the perfect Beldon 8450 shielded, two conductor, 22AWG, solid core wire. With a little AI help.
The supplier sells it in one foot lengths. Now it can be wire wrapped, secure and OEM.
I’m going to need 65 feet. The Beldon cable I have is stranded and it’s not working out.

NNC is the supplier I bought the shielded wire from. Awesome service from these people. An hour after placing the order I get a text from one of the buyers saying that they are out of that product but they can purchase it from a competitor but it will cost an extra $10 for logistic reasons. I had ordered 65 feet. So I added 35 feet making It 100 feet total and the bill was only $20 more due to the quantity discount.
Hit me up first if you need a few feet.

 

[Keith13]

Awesome that you've taken over this project Good luck

 

[tarior]

Through your post I found the perfect shielded, two conductor, 22AWG, solid core wire. With a little AI help.
The supplier sells it in one foot lengths.
I’m going to need 65 feet. The Beldon cable I have is stranded and it’s not working out.

Solid core is nice in that it stays put and looks really tidy. I might just use that product in future projects.

 

[zebulon1]

I had to revisit this thread.
Looking for some correct hardware.