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ChrisR1983 4th August 2009 02:00 PM

Tubelab Simple SE - Transformer Assistance
Hi All,

My first post!

Just finishing building some rather nice speakers using scan-speak drivers. They're amazing... I'm now about to build a shiny new Simple SE valve amp for them.

Completely new to this kind of thing so looking for some advice.

I'm in the UK and my speakers are 8Ohm. Can someone advise the part number for both a 240v transformer and the OPT from Edcor please?

I'm going to build a chassis from Welborne Labs; can anyone suggest alternative chassis? Cost is not an issue and neither is location, as long as they ship to the UK.



boywonder 4th August 2009 04:24 PM

Chris: The search button is your friend, there are zillions of posts here concerning transformers for the Simple SE.

If you don't mind a hammond, a 374BX would probably do the trick, it's universal voltage input and 375-0-375 @ 175ma output. Others here can address whether Edcor makes a 240V power transformer.

What sensitivity are your scanspeaks? Keep in mind that the simple SE is a fairly low power amp (around 6-8 watts or so), and is happiest with speakers that are fairly sensitive, depending on your listening habits.

Tubelab George has lots of tube and transformer info on his web page here:

boywonder 4th August 2009 05:22 PM

Re: Tubelab Simple SE - Transformer Assistance

Originally posted by ChrisR1983
Can someone advise the part number for both a 240v transformer and the OPT from Edcor please?


You want a 5K/8 ohm SE transformer. For the CXSE Edcors, the P/N is CXSE25-8-5K

(25 watt, 8 ohm secondary, 5K primary)

Alternatively, you could go with an Edcor CXSE25-8-3.2K (3.2K primary impedance) for a little more power out and a little more distortion.

Study the tables on the bottom of the page on Tubelab George's link posted above, and note the relationship between B+, power out, distortion, load Z (this is your OT primary impedance) and Rk (cathode R).

The above info assumes that you want to run EL34's/KT88's/6L6GC's.....

ChrisR1983 4th August 2009 07:30 PM

Thanks for the reply; I was in a rush writing the post as I was about to go into a meeting at work and realized that it was quite rude of me to demand this information. I'll have a thorough search and check back if I get stuck.

Regarding the sensitivity of the speakers it hovers around the 86-91dB mark. How will this effect things?



CharleyW 4th August 2009 07:32 PM

You may want to re-think ordering from Welborne Labs.

pointy 4th August 2009 07:46 PM

if the money is no object................and they are very good to talk to

boywonder 4th August 2009 07:49 PM


Originally posted by ChrisR1983

Regarding the sensitivity of the speakers it hovers around the 86-91dB mark. How will this effect things?



86-91 db is a huge range.......Most Scan-Speaks that I am aware of are around 87-88 db or so, although I'm not expert on these. Going from 88 db sensitivity to 91 db sensitivity doubles the volume for the same watts input to the speaker, so if you are hoping to crank Motley Crue with a SimpleSE and 87 db sensitivity you may be disappointed.

To generalize, if your speakers were 98 db sens, a SimpleSE would be more than enough power to blast your head off under reasonable home listening conditions, although many people are happy with 5-8 SE watts into 90-93 db speakers. These folks are typically not cranking up heavy metal, etc.

Going from 88db to 94 db sensitivity quadruples the volume for a given power. (SPL doubles every 3 db)

You may want to search the forum for Wellbourne labs posts before ordering.....

wa4swj 5th August 2009 01:08 AM

If I may, I'd like to agree with the comments about Welborne Labs.

Regarding the output transformers, I just built a Simple SE using Transcendar Transformers and they are quite good. I'm very pleased with the sound.


boywonder 5th August 2009 04:16 AM

Chris: Here is a link related to the SimpleSE and speaker sensitivity:

ChrisR1983 5th August 2009 03:22 PM

Thanks guys - some really useful information. I searched regarding Welbourne Labs. I wont be ordering my chassis from those guys then!!

Does anyone else know of a supplier that sells wooden enclosures that will ship to the UK?



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