4K or 5K Output Transformer

el156 · 19th May 2010, 11:11 AM

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

azazello · 19th May 2010, 12:33 PM

You can use 5 kohm, You will little bit lost only power, but bass will sound
better!

revintage · 19th May 2010, 12:41 PM

I don´t 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.

Yvesm · 19th May 2010, 12:57 PM

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.

el156 · 19th May 2010, 01:32 PM

Quote:

Originally Posted by revintage

I don´t 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

revintage · 02:15 PM

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 don´t expect low distortion with the above figures either.

el156 · 19th May 2010, 02:26 PM

Quote:

Originally Posted by revintage

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 don´t 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

revintage · 19th May 2010, 02:35 PM

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.

el156 · 19th May 2010, 02:46 PM

Quote:

Originally Posted by revintage

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

azazello · 19th May 2010, 04:54 PM

Quote:

Originally Posted by azazello

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.

19th May 2010, 11:11 AM	#1
el156 diyAudio Member Join Date: Apr 2010 Location: ALBUFEIRA ;PORTUGAL	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

19th May 2010, 02:12 PM	#6
revintage diyAudio Member Join Date: May 2007	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 don´t expect low distortion with the above figures either. Last edited by revintage; 19th May 2010 at 02:15 PM.

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19th May 2010, 12:33 PM	#2
azazello diyAudio Member Join Date: Aug 2008 Location: Bulgaria	You can use 5 kohm, You will little bit lost only power, but bass will sound better!

19th May 2010, 12:41 PM	#3
revintage diyAudio Member Join Date: May 2007	I don´t 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.

19th May 2010, 12:57 PM	#4
Yvesm diyAudio Member Join Date: Jul 2004 Location: Ardeche	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.

19th May 2010, 02:35 PM	#8
revintage diyAudio Member Join Date: May 2007	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.