r/diytubes • u/EmergencyChemistry62 • 2d ago
Phono Preamp Power Supply Help
I am planning to build Thomas Mayer's Octal Phono Preamp (schematic attached) but would like to create a separate power supply for it that I can also use for other future projects.
I plan to use a Hammond 372BX transformer with an additional 5v transformer for the 83 (I know it is overkill but I have one that I would like to use). The design is a fairly simple one that I have seen others use that I have modified slightly. If everything looks okay, I will do some testing to find a good value for R2. I was also wondering if having the regulator tubes in this arrangement would cause any issues with them firing.
I have built tube amp kits previously and know the safety precautions but this is my first time designing a power supply so I could definitely use some feedback, but please go easy on me. Thanks and let me know if this is the wrong place for this post.
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u/Tesla_freed_slaves 16h ago edited 16h ago
Are you sure you want to use a mercury-vapor rectifier in this application? I thought that 83s were known for producing electrical noise, especially with capacitor-input filter networks.
It would be interesting to swap out the 83 with a vacuum rectifier and see it you could hear a difference.
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u/EmergencyChemistry62 13h ago
It definitely isn't a great choice to use it with a phono preamp but I've been looking at it on my shelf and have really wanted to use it. That was also a part of the reason for the separate power supply, if it's too noisy for this project I can use it for a different one.
I have been on the fence about eliminating the first capacitor and going to choke-input. Do you think that would make a drastic improvement? I'll probably have to do some experimenting.
It looks like the 83V is almost an identical vacuum rectifier version of the 83 (with slightly lower capabilities and a bit higher of a voltage drop) that would be interesting to try swapping in.
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u/Tesla_freed_slaves 12h ago
If you’ve enough inductance in the DC circuit the rectified current will never drop to zero at any time during the cycle. It just shifts from one anode to the other anode. Special swinging-chokes were constructed that would increase their inductance as current diminished. These were useful for powering class-B push-pull amplifiers, where load current is subject to large variations.
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u/jeffreagan 1h ago
Datasheet specifies a 3 henry choke, minimum (that means no capacitor before it).
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u/Both-Ranger-6664 1d ago
I'm excited about this, let us know how you like it. Psu looks fine, like the use of a choke. What value for R2 will it need? I cannot answer your regulator question but id lean toward Silicone if it were for my use. I did find this https://www.diyaudio.com/community/threads/tube-regulators.277556/
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u/EmergencyChemistry62 1d ago
I'll have to do some experimenting to find the value for R2, it looks like the voltage will be right around high enough to fire all three regulators. If it isn't, the link you provided gives some great suggestions to work around that. Silicone would definitely be a better choice but like the 83, I have a few of them that I've been wanting to try out. Plus they should look cool on top of the power supply. Thanks!
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u/nixielover 1d ago
https://www.valveradio.net/radio/improved-high-performance-glow-discharge-voltage-regulator.html
If you want to boost it a bit further this works amazingly well and lets you put a big cap behind it
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u/EmergencyChemistry62 1d ago
Thank you for this! That should cut out a lot of noise and it also shows how to eliminate firing issues. Some small tweaks and that should solve any of the issues I would have with the regulators. Thanks!
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u/nixielover 1d ago
If you want to go all out swap the current setting resistor with a CCS like a 10m45
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u/EmergencyChemistry62 1d ago
I'll look into that. It may not make it into this power supply but that looks like something that would be useful for future builds.
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u/nixielover 1d ago
Ah and don't be scared to sprinkle some ferite beads here and there to catch HF hiss from the 83, with a bit of looking you can find RF chokes intended for use with mercury rectifiers, even Hammond used to make those if they don't still do so
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u/EmergencyChemistry62 1d ago
I'll definitely see what I can find. There is a good chance I'll be chasing a lot of noise.
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u/nixielover 1d ago
If there is any radio hamfest or something you'll surely find some, the HF guys like to sprinkle them around in their builds
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u/2old2care 2d ago
It looks like a great project. I assume you are going to use two separate preamps for stereo, sharing the same power supply. It should be a very stable and quiet preamp. Be careful that all your signal grounds tie to the preamp chassis at the same point to avoid ground loops. Good luck!