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Old 3rd August 2010, 06:31 PM   #1
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Default A few questions about transformer placement in an S5 K-12 tube amplifer

Hi all, I'm working on an S5 K-12 tube amplifier kit, and I have a few questions about transformer placement in the box. My current plan is to build an enclosure with four pieces of wood cut on 45's with an aluminum plate as the top. Then I'll have the four tubes emerging from the top of the case, and the 3 transformers mounted upside down on the aluminum plate behind the PCB / tubes. As I haven't seen any cases built like this in my travels (since most decide to mount the transformers on top of the case), I wanted to make sure this was an acceptable layout. The bottom would be left open for convection cooling.

This is similar to what I want to do, except there would be no raised portion behind the tubes, only screws in the plate where the transformers are attached beneath:

Click the image to open in full size.

Thanks so much for your help!
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Old 3rd August 2010, 06:48 PM   #2
TheGimp is offline TheGimp  United States
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Looking at the kit built here:

S5 Electronics K-12M Tube Amp

I see they have the transformers inside a metal enclosure. Based on that I don't think you will have problems but I would suggest two things. (1) rotate the opts 90 degrees with respect to the power transformer, and (2) add some small hole patterns for air to escape the top plate to allow for convection to help cool everything.
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Old 3rd August 2010, 06:52 PM   #3
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What do you mean by the "opts" and also, is there a specific layout in regards to the 3 transformers that allows for less signal noise? Thanks so much for the quick response
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Old 3rd August 2010, 07:01 PM   #4
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opts = output transformers
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Old 3rd August 2010, 07:06 PM   #5
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Ah, thanks for the lingo refresher . So, as a followup, would this type of layout work, with the only exception being the transformers and capacitors mounted upside down?

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Old 3rd August 2010, 07:52 PM   #6
TheGimp is offline TheGimp  United States
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In this case the three transformers are allgined the same, and will maximize magnetic coupling. Rotate the two right most (OPTs) 90 degrees to help cut magnetic coupling and reduce hum.
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Old 3rd August 2010, 08:19 PM   #7
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So, it is a bad idea to put the output transformer near the power transformer??
To save place, I want to put my two transformer on each side of the power transformer at just 5mm of distance???
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Old 3rd August 2010, 08:25 PM   #8
TheGimp is offline TheGimp  United States
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Yes, it is bad to have them close together. in addition, Rotate them so that the output transformer cores are 90 degrees to the power transformer core!

- | - or | - |

The closer they are to each other, the greater the magnetic coupling and the more hum the power transformer will induce into the output transformers.
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Old 4th August 2010, 12:22 AM   #9
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Wait, wouldn't it be | - - with the power transformer on the left and the two output transformers on the right?
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Old 4th August 2010, 02:39 AM   #10
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Yes, TheGimp was answering arold19's question. Your proposed layout should be | - -
or - | |

You will definitely want some vent holes in the top plate now that you have transformers under there

Last edited by rotaspec; 4th August 2010 at 02:41 AM.
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