Hello, this is a question about a random thought I had.
Can Turret board construction cause more cross talk and noise than point to point wiring or PCB? I know the turrets are typically several mm apart, but all of the components carrying the signal are typically mounted in parallel to each other.
Any thoughts/equations to help me think about this concept more thoroughly?
Can Turret board construction cause more cross talk and noise than point to point wiring or PCB? I know the turrets are typically several mm apart, but all of the components carrying the signal are typically mounted in parallel to each other.
Any thoughts/equations to help me think about this concept more thoroughly?
Definitely, there is longer wiring and sub-optimum component layout, with large loop areas,
no ground plane, and lots of parasitics and noise pickup.
The only real advantage of turret boards is their ease of repair, and somewhat better ruggedness.
no ground plane, and lots of parasitics and noise pickup.
The only real advantage of turret boards is their ease of repair, and somewhat better ruggedness.
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Thats what I was thinking.
Are there any guides that you know of for designing pcb's for high voltage tube circuits? I've only ever done low voltage designs, and I wouldn't really know where to begin with trace width, trace spacing, keep outs, ground planes, etc.
The largest difference from low voltage pcb layout is the creepage and clearance required.
This will vary for each design, and for the exact location on the pcb. Normally HV should
be avoided for internal pcb layers.
https://blog.optimumdesign.com/clearance-and-creepage-rules-for-pcb-assembly
Of course tube circuit impedance levels are in general much higher, so the parasitics should
be kept to a minimum near high impedance nodes such as grids and plates. Possible
coupling between high impedance traces on the board should also be avoided.
https://www.ourpcb.com/high-voltage-pcb.html
https://resources.pcb.cadence.com/blog/2020-high-voltage-circuit-design-guidelines-and-materials
This will vary for each design, and for the exact location on the pcb. Normally HV should
be avoided for internal pcb layers.
https://blog.optimumdesign.com/clearance-and-creepage-rules-for-pcb-assembly
Of course tube circuit impedance levels are in general much higher, so the parasitics should
be kept to a minimum near high impedance nodes such as grids and plates. Possible
coupling between high impedance traces on the board should also be avoided.
https://www.ourpcb.com/high-voltage-pcb.html
https://resources.pcb.cadence.com/blog/2020-high-voltage-circuit-design-guidelines-and-materials
The KiCad PCB calculator has a required distance calculating function, based on the IPC norm if I remember well.
If you should want to put highish voltages on an inner layer of a multilayer board (I have a DAC with a -300 V supply plane on an inner layer), it may be a good idea to use a double prepreg layer. The chance of having a void at the same place in both prepreg layers is much smaller than the chance of a void in a single layer. Eurocircuits uses double prepreg by default, it's a custom build-up for most of the other PCB manufacturers.
If you should want to put highish voltages on an inner layer of a multilayer board (I have a DAC with a -300 V supply plane on an inner layer), it may be a good idea to use a double prepreg layer. The chance of having a void at the same place in both prepreg layers is much smaller than the chance of a void in a single layer. Eurocircuits uses double prepreg by default, it's a custom build-up for most of the other PCB manufacturers.
Crosstalk yes, circuit noise no, crosstalk of interference yes.
Related question: is there anything to crosstalk? If you build the circuit in a well-shielded enclosure and if there are no internal sources of interference, turret boards may be perfectly acceptable. If there is a mains transformer in the circuit, that will of course be a source of 50 Hz or 60 Hz magnetic interference.
Regarding heater wiring with AC heater supply if you should go for a PCB: some just use twisted wires for the heater wiring and use the PCB for everything else.
In my DAC, I included heater traces in the PCB layout, but with an ABA type of layout where possible. That is, I split one of the heater traces into two parts, one to the left and one to the right of the other heater trace. Hopefully the magnetic fields caused by the two loops will then more or less cancel.
In my DAC, I included heater traces in the PCB layout, but with an ABA type of layout where possible. That is, I split one of the heater traces into two parts, one to the left and one to the right of the other heater trace. Hopefully the magnetic fields caused by the two loops will then more or less cancel.