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PostPosted: 27 Aug 2008, 09:33 
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Joined: 26 Aug 2008, 20:57
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Location: Atlanta
I am stuck...designing the PSU for my Aikido 5687 has just confounded me to no end.

I want to do 250v plate and 12v heater. I have already built a regulator stage with a 78T12 because the heaters on the 5687 and 6cg7 draw so much current that it would be at the peak of a regular 7812. Looks like I need nearly 2.2a on these and I guess a 15v tranny?

Also, what is the deal with everything being center-tapped and everything I want to do not needing one!!?? I have a 6x4 rectified PSU for the plate voltage but cannot find a 250v straight up transformer to supply it and I am confused on how the center tap works...would I want a 250-0-250 or something like a 120-0-120? Again lost! Clueless!

Any help would be greatly appreciated and any resources I can read would also be appreciated. Everything I do I learn by reading and doing and this high voltage thing is not something I want to screw up!!

I do mess with 480v 3phase at work but control trannys are simple...480 in, 120 out...I am almost tempted to "borrow" one and reverse power it from the 120 tap and hook up the primary to the 240 tap...what would happen there?


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PostPosted: 27 Aug 2008, 13:02 
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Location: Winnipeg, CANADA
billnchristy wrote:
I want to do 250v plate and 12v heater. I have already built a regulator stage with a 78T12 because the heaters on the 5687 and 6cg7 draw so much current that it would be at the peak of a regular 7812. Looks like I need nearly 2.2a on these and I guess a 15v tranny?

The 78T12 is a 3A regulator, so that should be fine. You will however need to provide a sufficient heat sink. The voltage drop is typically 3V so you will want to be at 15V or higher. Note the higher input voltages mean more heat.

billnchristy wrote:
Also, what is the deal with everything being center-tapped and everything I want to do not needing one!!?? I have a 6x4 rectified PSU for the plate voltage but cannot find a 250v straight up transformer to supply it and I am confused on how the center tap works...would I want a 250-0-250 or something like a 120-0-120? Again lost! Clueless!

These projects should give you some idea on how to use a CT transformer with a tube rectifier:
http://diyaudioprojects.com/Tubes/KT88/
http://diyaudioprojects.com/Tubes/5687/
Also, I have attached a the aplication note schematic for the 6X4.


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PostPosted: 27 Aug 2008, 21:06 
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Joined: 31 Jul 2008, 23:21
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Follow that schematic and you should be fine. You will want to look up the tube datasheet as it will contain all the information that you need. As noted on that schematic, do not exceed 40uF after the rectifier or you will exceed the inrush current. Place a choke after the 40uF cap to the get the right voltage and then your capacitor bank. This should be a rewarding project. I have read very good things about the Aikido linestage. The 5687 is a personal favorite of mine.


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PostPosted: 28 Aug 2008, 13:05 
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Joined: 26 Aug 2008, 20:57
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Location: Atlanta
I think I am going to stick to solid state but I am slowly figuring this stuff out!

I finally got to playing with PSU designer and was able to make things work with the trannys and chokes I have (phew).


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PostPosted: 28 Aug 2008, 15:55 
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Location: Atlanta
Ok, another rookie question...how do I figure out the load resistance?


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PostPosted: 28 Aug 2008, 20:00 
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Are you talking about the load in PSU designer?

If you are, you can use the current draw of the tube. Put a constant current rather than a resistance in the model.

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PostPosted: 29 Aug 2008, 06:54 
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Joined: 26 Aug 2008, 20:57
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Location: Atlanta
Ok, I think I got this figured out! (thanks all)

One last question.

I want to have several PC grade caps after the rectifier, if these are located after the final filter (mine only has an LC) that will not negatively affect the psu right?

Below is a rendition...should that cap bank be before or after the load or does it matter?


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PostPosted: 29 Aug 2008, 07:30 
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Typically you will see a cap after the diodes, then the choke and then more caps. The load is usually at the end or off of a capacitor.

Are you checking this with PSUD II?

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PostPosted: 29 Aug 2008, 07:47 
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Location: Atlanta
PSUD won't let you add a cap after the coil. The drawing is straight up off PSUD except the addition of the caps after the load...obviously they would not be after the load, but it was just easier to place them there.

I don't want them to be a filter, more of a power reserve...am I wrong? It seems like most PSU have a bank of caps for this reason and I have always gotten good results by having more energy reserve.


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PostPosted: 29 Aug 2008, 07:49 
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Joined: 26 Aug 2008, 20:57
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Location: Atlanta
Here is the chassis design...I will start a new build thread when the actual construction starts taking place.


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