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4K or 5K Output Transformer

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el156

el156

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Joined 2010
#1
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
 
#3
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.
 
#4
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 :2c:

Yves.
 
#5
revintage said:
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.
Click to expand...

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
 
#6
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.
 
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#7
revintage said:
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.
Click to expand...

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
 
#8
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.
 
#9
revintage said:
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.
Click to expand...

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
 
#12
I compared 2 amps PP KT88, one with EDCOR and sec. with Hammond1650.
I used test-generator and scop. Input ampl 1 v.
Hammond keeps constant amplitude 20-20000 Hz, but EDCOR - apr. 50-16000 Hz.
I prefer Hammond 125GSE - 100ma 76$ or more expensive from this brand 1628SEA - 120ma 120$
/I use Ham.125FSE in my SE 2A3 RCA and I haven't a problem with band 20-20000Hz/
 
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#13
Odd order harmonics should be decreased. So I was wrong about 5k. Go for a 3,5k, there are alot available.2nd order wil increase but that is no big problem. But you must probably change your working point. Check the datasheet and curves.
 
#15
4K or 5K ?

radiostar said:
I did a lot of experiments wit 307A ( VT225). It's declared like 4K on 250Volts and 4K5 on 300Volts on plates. I tried a lot of 4K, 4K5 and 5K transformers and I didn't see ant significiant difference.

Good luck with EL156!
Click to expand...

Thanks a lot ! I will make some experiments and i will start with 3,5K ,Telefunken says 3,8K with Va 450 V and 4K with 350V! There is not a big difference!
Silvino
 
#19
Joshua_G said:
I have Telfunken EL156 Data Sheet, alas, I don't read German.
Does it say there what is the tube's internal anode resistance in pentode mode and in triode mode?
Click to expand...
Hi !
Yes,i have datasheets for pentode mode and triode, i will post them as soon as possible. I can see in the SE schematic that the THD is 9%, but is for full power,and without NFB,so i think with little modification,this can be a very interesting Amp, with 25W in SE.
Thanks
Silvino
 
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