Scorpion Tube power Supply Build Thread

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Re: Scorpion Tube power Supply Build Thread

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Holger wrote:
Sun Nov 06, 2022 5:38 am
The Scorpion works wonderful in my 1 Ru mic pre.
Wow Holger that is a super neat and compact dual tube pre. Amazing.

(I copied the photos locally on to the forum as they weren't showing for some reason)
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STUDIO315
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Re: Scorpion Tube power Supply Build Thread

Post by STUDIO315 »

Hi Joe,

I am checking to determine if the Scorpion would be able to sufficiently power the Collins 356E-1.

The power requirements from the unit instructions are as follows:
300 vdc at 77 milliamperes
6.3 vac at 1.55 amperes

Any help in confirming would be appreciated.

Thanks,

Nathan

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Re: Scorpion Tube power Supply Build Thread

Post by STUDIO315 »

Ok - using the calculator Joe provided it appears this power supply would not be a good fit:

(21*1.55)+(320*.077)=57.19=meltdown

Nathan

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Re: Scorpion Tube power Supply Build Thread

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STUDIO315 wrote:
Mon Dec 12, 2022 7:24 am
Ok - using the calculator Joe provided it appears this power supply would not be a good fit:

(21*1.55)+(320*.077)=57.19=meltdown

Nathan
Yes correct. In the new year I will have a new HV supply that uses a normal off PCB toroid for the first transformer. So a 80VA or large can be used to run the filament and 48v phantom and so the whole 30VA can be used for the high volts which will work for a huge amount of vintage tube gear.
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Re: Scorpion Tube power Supply Build Thread

Post by willgmr »

Hi,
Is 300v the top output range based on the regulator or the VAC rating of the included transformer?
I have an old preamp that wants 320V at the first stage and 200V at the second.

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Re: Scorpion Tube power Supply Build Thread

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willgmr wrote:
Fri Apr 07, 2023 2:39 pm
Hi,
Is 300v the top output range based on the regulator or the VAC rating of the included transformer?
I have an old preamp that wants 320V at the first stage and 200V at the second.
There is 320vdc unreg available on the pcb but the 2 x 150v zeners in series limit the regulator to 300v.
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Re: Scorpion Tube power Supply Build Thread

Post by willgmr »

Thanks for the reply. Possible to change those zeners to 160V versions? Or add another 20V in series?

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Re: Scorpion Tube power Supply Build Thread

Post by Joe Malone »

willgmr wrote:
Fri Apr 14, 2023 6:09 am
Thanks for the reply. Possible to change those zeners to 160V versions? Or add another 20V in series?
You need to have some volts to regulate. So if you get 320v unreg (which will depend on the mains voltage where you are and the load on the hv rail) you could probably go to 310v by adding a 10v zener in series with one zener.

Remember if the original power supply was unregulated the 320v probably sags in use to less than 320v any way. So 300v regulated will be fine if not better for 99% of tube gear as it is on 5% out. In most tune gear I see +/-20% in power rails.
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Re: Scorpion Tube power Supply Build Thread

Post by willgmr »

Thank you for your input - I think you’re right regarding voltage sag and unregulated supplies. I will give this supply a try when I’ve got the time to open up this project. Thank you!

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Re: Scorpion Tube power Supply Build Thread

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willgmr wrote:
Fri Apr 14, 2023 2:02 pm
Thank you for your input - I think you’re right regarding voltage sag and unregulated supplies. I will give this supply a try when I’ve got the time to open up this project. Thank you!
Biggest thing is make sure you use the maths shown on the website to check the filament Watts and hv watts is total less than 30VA. If not sure ask me to check if it will work.

I am working on larger Scorpion which uses off pcb normal toroid for filament and pcb toroid for high volts to do bigger projects but it isn’t finished yet.
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Re: Scorpion Tube power Supply Build Thread

Post by willgmr »

Hello,

I’ve just built the scorpion supply and am getting it up and running with a vintage EAB VE12 mic preamp. I’m trying to just work on the preamp on the bench before racking it up so I don’t have proper heat sinking and I can’t get the Filament regulator to stay on - it’s getting too hot and the voltage is dropping. Can you recommend a heatsink size that will allow it to stay on comfortably? I am drawing 0.650A from the regulator with the two E283CC tubes.

Also, is there any issue in connecting one side of the heater filament to the same ground as B+? I know they are technically isolated but wondered if this can cause any noise or other issues?

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Re: Scorpion Tube power Supply Build Thread

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willgmr wrote:
Sun Dec 31, 2023 9:49 am
Hello,

I’ve just built the scorpion supply and am getting it up and running with a vintage EAB VE12 mic preamp. I’m trying to just work on the preamp on the bench before racking it up so I don’t have proper heat sinking and I can’t get the Filament regulator to stay on - it’s getting too hot and the voltage is dropping. Can you recommend a heatsink size that will allow it to stay on comfortably? I am drawing 0.650A from the regulator with the two E283CC tubes.

Also, is there any issue in connecting one side of the heater filament to the same ground as B+? I know they are technically isolated but wondered if this can cause any noise or other issues?
You need 5C/W heatsink. Basically a thick 5mm or more thick slab of aluminium as large as the scorpion pcb. It is ideal to bolt this slab of aluminium to the side of the rack case so heat can escape and the case should have top vent holes. The Regs and Fets must always be heatsinked before load applied or regs will thermal on and off and get weaker and Fets will fail. Only the 2 long screws into the transformer underside are needed to clamp the regs and Fets down to heatsink in there thermal silicon tubes tightly for heat transfer.
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Re: Scorpion Tube power Supply Build Thread

Post by willgmr »

I tried a heatsink like the one linked below which claims 7 C/W on the datasheet but it only helped a little bit

https://www.mouser.com/ProductDetail/Wa ... A84w%3D%3D

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Re: Scorpion Tube power Supply Build Thread

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willgmr wrote:
Sun Dec 31, 2023 11:01 am
I tried a heatsink like the one linked below which claims 7 C/W on the datasheet but it only helped a little bit

https://www.mouser.com/ProductDetail/Wa ... A84w%3D%3D
The linked heatsink states “ Thermal Resistance: 25 C/W” It is so low in mass it will do very little. You want as much heatsink as possible. Like the size I stated above.

When we rack 6.3v dual tube preamp gear we re-wire them to series 12.6v filament as this quarters the wasted heat wattage so needs less heatsinking.
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Re: Scorpion Tube power Supply Build Thread

Post by willgmr »

I’ve got the scorpion up and running now with it bolted to a 1/4” bar of aluminum.
The heater voltage seems solid, but I’ve got HV2 cranked as high as it will go, and under load it stops at 256V. I’ve got 266V unregulated at the power resistor and 116VAC at the outlet (USA).
Does this seem correct under load?
IMG_4353.jpeg
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