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Old 19th May 2010, 11:11 AM   #1
el156 is offline el156  Portugal
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Default 4K or 5K Output Transformer

HI All !
I would like in Near Future to make a single ended amp with EL156, but i cant find a cheap transformer 0f 4K! The ones i found are Bartolucci an very expensive! And the question is, can i use a 5K instead of 4K ? does it cause problems or just lost of power?
The power should be 25W and 100 ma DC pass!
Thanks
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Old 19th May 2010, 12:33 PM   #2
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You can use 5 kohm, You will little bit lost only power, but bass will sound
better!
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Old 19th May 2010, 12:41 PM   #3
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I donīt know if you will run pentode, UL, Schade or triode? Just use the Ua/Ia curves to find out. You can then double check the results i Spice.

I have just designed an EL156 Schade with E280F driver and that one is 425V/5k/100mA.

I would advice you to go 5k just as azazello recommends.
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Old 19th May 2010, 12:57 PM   #4
Yvesm is offline Yvesm  France
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An output transformer has no impedance by itself, it just multiplies the one of the loudspeaker by a more or less frequency dependent constant factor.
So, you must consider at first the real impedance of your loudspeaker system wich may also change by a factor as high as five along the frequency range.
In front of that, 4 or 5K is "peanuts".
My

Yves.
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Old 19th May 2010, 01:32 PM   #5
el156 is offline el156  Portugal
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Quote:
Originally Posted by revintage View Post
I donīt know if you will run pentode, UL, Schade or triode? Just use the Ua/Ia curves to find out. You can then double check the results i Spice.

I have just designed an EL156 Schade with E280F driver and that one is 425V/5k/100mA.

I would advice you to go 5k just as azazello recommends.
Hi !
I want to use the El156 as pentode with Va 450V ,Ra 4K, Rk 90 Ohms, and i should have 25W in class A! But if i use Ra of 5K instead of 4K ,do i have the same results? Can you recommend a nice (and cheap transformer to do the job?
Thanks
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Old 19th May 2010, 02:12 PM   #6
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Theoretically you will get in the ballpark of 20W with 4k and maybe 2W lower with 5k. So the difference will be very small using Us=350.
The 25W mentioned is probably with gross and unaccetable THD. But donīt expect low distortion with the above figures either.

Last edited by revintage; 19th May 2010 at 02:15 PM.
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Old 19th May 2010, 02:26 PM   #7
el156 is offline el156  Portugal
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Quote:
Originally Posted by revintage View Post
Theoretically you will get in the ballpark of 20W with 4k and maybe 2W lower with 5k. So the difference will be very small using Us=350.
The 25W mentioned is probably with gross and unaccetable THD. But donīt expect low distortion with the above figures either.
THANKS
I want to make this amp with original telefunken schematic! And they say that with this circuit we will have 25W in class A, but i will be very happy if i have at least 10W with an accetable THD! Any suggestions for the output transformers?
Thanks a lot
Silvino from Portugal
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Old 19th May 2010, 02:35 PM   #8
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Hey Silvino,

As Swede I of course recommend Lundahl but there must be lot to choose from out there. If you want something in the lower pricerange a Mars from vt4c could do. Have a few friends who tried them and they seems descent.

Do you have the original Telfunken schematic? Would be nice if you could publish it here.
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Old 19th May 2010, 02:46 PM   #9
el156 is offline el156  Portugal
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Quote:
Originally Posted by revintage View Post
Hey Silvino,

As Swede I of course recommend Lundahl but there must be lot to choose from out there. If you want something in the lower pricerange a Mars from vt4c could do. Have a few friends who tried them and they seems descent.

Do you have the original Telfunken schematic? Would be nice if you could publish it here.
Hi again!
Yes , i have all the original telefunken schematics! i will post them as soon i have my scanner working! And i also have the original Telefunken El156! I only needed the sockets , but i recently bought them from Holland in JUKEBOX-REVIVAL !
Thanks
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Old 19th May 2010, 04:54 PM   #10
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Quote:
Originally Posted by azazello View Post
You can use 5 kohm, You will little bit lost only power, but bass will sound
better!
and You will decrease little bit second harmonic for better reality.
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