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Old 16th April 2009, 10:34 PM   #1
skipper is offline skipper  United States
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Default Simple SE PWR Tansformer

Hi All,

I am in the planning stages of building a Simple SE. I plan on using the KT88 and the Edcor CXSE25-8-5K. After reading many threads I see that my power options as these three below.

Hammon 274BX 375-0-375 @ 175mA 5.0 @3A 6.3V@6A
Allied 6K7VG 750 VCT @150mA 5V@3A 6.3@5A
Edcor XPWR035 370-0-370 @200mA 5V@2A 6.3@5A

I want to use the Edcor since I will be purchasing the OPT from them. I see they have a higher current, 200mA than the other two but the 5V output is only 2A. Should I be concerned with this, what is more important the 200mA value or the rectifier amperage?


skipper
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Old 16th April 2009, 11:08 PM   #2
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For KT88, you'll want at least 70 mA per tube, plus ~10 mA per side of the 12AT7. That makes 160 mA minimum. It is useful to know that a power transformer rated for a given current at 50 Hz operation is capable of delivering more current when run on 60 Hz. This means you'll be able to get enough current out of the Allied, even though it's "only" rated 150 mA.

I'd avoid the Hammond 274BX. They seem to be developing a reputation of being "noisy", mechanically. They can make a humming or buzzing noise under certain circumstances.

I used a Hammond 374BX for my Simple SE. I am very pleased with it, but it was expensive. It seems well suited for the KT88 power tubes.

I know little about the Edcor power transformers.

The 5V winding is only used by the rectifier tube. If you use a 5AR4, then 2 amps is adequate. If you want to try a 5U4, you'll need 3 amps. I'm not sure why you'd want to use a 5U4, as it adds extra voltage drop - which isn't something you'd need for KT88. If you intend to use the solid state FREDs for rectification, you won't need the 5V winding at all. I wouldn't recommend using the FREDs, though.
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Old 16th April 2009, 11:34 PM   #3
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I picked up the edcor xpwr059
375-0-375 , 175 mA 50V .05A 6.3V CT 6A 5V CT 3A
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Old 17th April 2009, 12:06 AM   #4
chrish is offline chrish  Australia
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The XPWR059 looks to have the same spec as the Hammond 374BX. It has windings for 240 volt and 120 volt primary 50/60 Hz. As it is made for 50 Hz it should have a little more iron and therefore be a little more conservatively rated for 60 Hz so should be a good choice.

Chris
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Old 17th April 2009, 01:21 AM   #5
rknize is offline rknize  United States
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As you are probably aware, I went with the Edcor XPWR035. It barely gets warm after several hours, so it has plenty of capacity for the job. If you want the option of using a different rectifier, such as one from the 5U4 series, then having 5V @ 3A is required. However, the recommended 5AR4/GZ34 is favored for its lower tube drop and slower warm-up, which gives plenty of time for the other tubes to get their cathodes hot before B+ arrives. The core and bobbin are *exactly* the same dimensions as the CXSE25-8-5K, so the three go well together.
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Old 17th April 2009, 09:46 AM   #6
RDL_AK is offline RDL_AK  United States
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Hi, I don't see any of the EDCOR transformers listed in this threed on the EDCOR website. Are these special order?
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Old 17th April 2009, 12:27 PM   #7
rknize is offline rknize  United States
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All of their transformers are made-to-order, as I understand it. Only a few of their power transformers are listed on the web page. They have more listed in a PDF that was posted in thei forums.

Russ
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Old 17th April 2009, 12:56 PM   #8
chrish is offline chrish  Australia
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Link to the pdf
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Old 17th April 2009, 04:39 PM   #9
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Thanks for the link, Chris- I had a good look around the Edcor site and couldn't find it.
Cheers
John
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Old 18th April 2009, 02:02 AM   #10
RDL_AK is offline RDL_AK  United States
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Thanks for the information and the link. :wave
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