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Edcor CXSE25-8-2.5K single ended UL transformer
Edcor CXSE25-8-2.5K single ended UL transformer
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Old 3rd February 2012, 08:03 PM   #1
joseangel is offline joseangel  Spain
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Join Date: Feb 2012
Default Edcor CXSE25-8-2.5K single ended UL transformer

Hi all,

First of all, I'd like to say thanks for the nice and very interesting forum you have here! I have been a time attending in read-only mode, but finally jumped in and register!

I have a solid EE background and some experience in analog design, however, this is my first time on audio tubes design. I am planning to design and build a nice SE amp for a close friend of mine (and myself also, of course). I'm really excited with this great opportunity for learning new things and put hands down on a diy project.

Let's get to the point. I have nailed down the selection of the tubes and SE transformer: I will most probably use 2x KT88 per channel and an Edcor CXSE25-8-2.5K. On the paper (transfer curves) it shows the right balance:

- Very low distorsion at 1,25 K Zpri equivalent per output tube and channel.
- Low static power dissipation for each tube (Wa+g2), hence, assuring a long life (I never liked to put a device under close to max. rating specs).

My questions are:
1) What is your experience with Edcors and KT88 in SE UL configuration. Which Ia,g2 polarization current you chose?
2) I cannot really understand the specs for this transformer. Well, I mean the specs are very thin. Edcor's website states this CXSE25-8-2.5K model is rated for maximum 200 mA. But... Is it maximum DC operating CONTINUOUS (average) current? Or maximum current (DC + AC peak) current? In the first case I will go with 50 mA steady current for each KT88 and channel, but in the second I may grow up until 100 mA per KT88 and easily.
3) Same question about 25 W max. rating? Is it continuous (RMS) power? Or peak (musical) power?

Best regards,
Jose Jimenez
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Old 4th February 2012, 03:55 AM   #2
jamesdb is offline jamesdb  United States
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Join Date: Jun 2007
The Edcor website has a forum, they can better answer these for you.
EDCOR Electronics Corporation. Forums
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Old 4th February 2012, 04:05 AM   #3
tomchr is offline tomchr  Canada
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Location: Calgary
I agree that Edcor's "specs" are a bit thin. That's what $70 buys you....

I have experience with the CXSE25-8-5K and a 300B. I'm running 90~100 mA DC bias without issues.

Modulus-86: 40W/8Ω @ 0.000061% THD. HP-1: 3W/20Ω, 450mW/300Ω @ 0.000032% THD. DG300B and Other Tube Circuits.
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Old 4th February 2012, 03:38 PM   #4
joseangel is offline joseangel  Spain
diyAudio Member
Join Date: Feb 2012
Thanks for your nice answers. I didn't notice that Edcor's website had a forum. I will post my questions there and will afterwards complete here the answer I can get from them!

Tom, it is great to know you have run it at 90-100 mA DC bias with no issues. I was secretly hoping that the Edcor's could support up to 200 mA DC bias (which I am sure cannot, tough I will try to confirm it), so as to pump up the maximum output power.

Do you know of any other "budget" SE UL transformer able of sustaining 200 mA DC? As this is my first serious project with tubes I am trying to stick to a <600$ budget for the whole amp. :-)

Best regards,
Jose Jimenez
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