I'm thinking through the layout of a phono preamp, and I had a weird idea re: tube orientation. My understanding is that the rule of thumb for tube placement is to have 1.5 tube diameter separation between tubes. That assumes the tubes' bases are mounted in the same plane. I have this idea to have the tubes mounted sideways with the tops facing each other in opposition. The spacing would be fairly minimal, but allowing enough space to remove/replace tubes as necessary.
The next layer to this question is re: the rectifier tube for the same amplifier. In the same thought bubble, that tube is oriented in the same plane across the vertical centers of the preamp tubes, but 90° out like so:
_!_
Where you're looking down over the top of the amplifier, and the top of the ! is the rectifier tube. The dot of the ! is where a line drawn through the vertical center of the three tubes would meet.
An alternative to this would be to have all three tubes mounted in a ring such that it's an even 120° between each tube rather than 90° with only three quadrants populated.
How stupid is this? Would either scenario cause any issues? Accidentally solve any issues? How much separation would there need to be between tubes/types of tubes to avoid causing problems if there are problems being caused?
A third alternative would be to have the amplifier tubes in one plane, and the rectifier in another a la:
=
but I think that would result in the same spacing requirements as if the bases were all co-planar.
The next layer to this question is re: the rectifier tube for the same amplifier. In the same thought bubble, that tube is oriented in the same plane across the vertical centers of the preamp tubes, but 90° out like so:
_!_
Where you're looking down over the top of the amplifier, and the top of the ! is the rectifier tube. The dot of the ! is where a line drawn through the vertical center of the three tubes would meet.
An alternative to this would be to have all three tubes mounted in a ring such that it's an even 120° between each tube rather than 90° with only three quadrants populated.
How stupid is this? Would either scenario cause any issues? Accidentally solve any issues? How much separation would there need to be between tubes/types of tubes to avoid causing problems if there are problems being caused?
A third alternative would be to have the amplifier tubes in one plane, and the rectifier in another a la:
=
but I think that would result in the same spacing requirements as if the bases were all co-planar.
You don't want the rectifier tube (and associated wiring) anywhere near the audio tubes and circuitry.
Its orientation relative to the audio tubes doesn't matter, because it should be far away.
Its orientation relative to the audio tubes doesn't matter, because it should be far away.
Preamp tubes really do not need space for air. They typically need space for many small parts and to avoid regeneration.
Separation between the power supply and amplifier channels is part of the reason for doing this. In my head, I'm building this in a pseudo mono-block configuration. Imagine the ~1 ft^2 footprint of a turntable with a cutout front and center into which the tubes project such that it's a squatty U-shape on its side. Approximately half of the footprint (the bottom of the U) is the power supply, with all the transformers/chokes/large format capacitors inside the enclosure and the rectifier tube projecting into the center of the U from the bottom. The legs of the U are the channels of the amplifier.
The reason to space the tubes out is to avoid magnetic interference, but magnetic fields have a shape/directionality to them. If all of the tubes are in the same orientation in the same plane, the standard spacing recommendations apply. If they're oriented as described, what does that do to the desired spacing? How far is far enough generally speaking, and would this arrangement make that more or less?
The reason to space the tubes out is to avoid magnetic interference, but magnetic fields have a shape/directionality to them. If all of the tubes are in the same orientation in the same plane, the standard spacing recommendations apply. If they're oriented as described, what does that do to the desired spacing? How far is far enough generally speaking, and would this arrangement make that more or less?
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For RIAA it is recommended to use sockets with shields . But strong magnetic fields from transformers , chokes shouldn't be near as it is very hard or impossible to shield a RIAA circuit against this .
There won't be significant magnetic fields generated from audio operation of a miniature tube.
Consider the capacitive interaction between the sections of a dual triode instead.
It seems you are a purist. 😀
I would not use a power supply with rectifier tube in a preamp design. A SMPS with switching frequency high enough over the audio bandwidth range will do it better. It is cheaper, les bulky and does not inject 50Hz or 100Hz from the mains in the audio stages.
This is my first dive into this domain, and I'm learning all this stuff for the first time. I wouldn't say I'm a purist so much as that I'm trying to learn analog circuitry, and a solid state rectifier doesn't help with that goal. Coming out the other end with a nice little phono preamp is just a nice bonus.
If the tube spacing consideration is thermal, I should be plenty fine. If anything, I'm coming out ahead of the game even with the smallest space I can get away with and still be able to replace tubes.
Just to be clear though, the rectifier tube (a 6CA4 for what it's worth) is also not expected to be an issue in the above diagramed configuration? I figure, as it's laid out, the transformers and such will all be at least as far away as they would in a more conventional layout (everything sitting on top of an enclosure), and have the bonus of a grounded brass (or whatever I end up using) plate or two in the way to boot.
If the tube spacing consideration is thermal, I should be plenty fine. If anything, I'm coming out ahead of the game even with the smallest space I can get away with and still be able to replace tubes.
Just to be clear though, the rectifier tube (a 6CA4 for what it's worth) is also not expected to be an issue in the above diagramed configuration? I figure, as it's laid out, the transformers and such will all be at least as far away as they would in a more conventional layout (everything sitting on top of an enclosure), and have the bonus of a grounded brass (or whatever I end up using) plate or two in the way to boot.
I think if this is your first build you should aim to build something that is straightforward, and build it in a standard way. If the time comes and you start to chase issues, it will be a lot more straightforward to get support if you have not introduced new variables into the design.