LE-300BXLS-SE

About the Emission Labs tubes and how to use them.

LE-300BXLS-SE

Postby hlcs25 » Sun Mar 10, 2013 10:49 pm

Hi Jac,

I am planning to build LE-300BXLS-SE with EML-300b-XLS-V4 center tapped heating tubes. How the schematic has to be modified to this? I suppose the R13-R14-R15+POTI 1 can be substituted by 1 pce 11 Ohms resistor or 2 pcs 22 Ohms parallel. Am I right?.

Can the feedback C4-R16-R17 be omitted? Or would it be useful to make it switchable?

I saw on a Tubelab SE schematic and another one as well that there is a Cool MOS Power Transistor (SPA11N60C3) between coupling capacitor and grid resistor of 300B. I would like to have your opinion about it.

Thanks.

Kind regards, Gabor
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Re: LE-300BXLS-SE

Postby J. Leven » Mon Mar 11, 2013 8:49 am

I saw on a Tubelab SE schematic and another one as well that there is a Cool MOS Power Transistor (SPA11N60C3) between coupling capacitor and grid resistor of 300B. I would like to have your opinion about it

Hi,
have you a Link to this schematic ?
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Re: LE-300BXLS-SE

Postby Admin19 » Mon Mar 11, 2013 10:09 am

http://4tubes.com/SCHEMATICS/LUNDAHL-TR ... Gesamt.pdf

Hello Gabor,

the schematic is by Mr. Leven, and any changes to it, you should carefully discuss with Mr. Leven. I can only give some initial ideas.

The principle with the V4 tubes is a simple one. In many schematics, the heater center tap is needed, but there is no connection to it. So the circuit designer has to create it artificially, outside the tube. There are many ways.

In Mr. Leven's schematic, this is done with resistors R13 + R15, and the artificial center tap is where the green dot is. (TP 49,3 Volt). In short, just remove R13 and R15 and connect the center tap to TP1.

Keep in mind, if you ever don't not want to use the center tap of the 300B-XLS-V4, all you need to do is NOT connect it. If you just "forget" the center tap connection, you can regard it a normal 300B-XLS in an octal socket. So you can always begin by trying out the original ciruict, even when you have the 300B-XLS-V4.

-Jac
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Re: LE-300BXLS-SE

Postby hlcs25 » Tue Mar 12, 2013 9:03 pm

Hi J.L.

The link is:
http://www.tubelab.com/TubelabSE.htm
and description of PowerDrive:
http://www.tubelab.com/powerdrive.htm
And a similar schematic:
http://diyaudio.hu/forum/download/file.php?id=1625

I hope it is an interesting one.

I had another question: Can the feedback C4-R16-R17 be omitted? Or would it be useful to make it switchable?

Regards, Gabor
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Re: LE-300BXLS-SE

Postby hlcs25 » Tue Mar 12, 2013 9:29 pm

Hi Jac,

Thanks for the infos. EML 300B-XLS-V4's pin 8, the center tap (cathode) is connected to TP1 through R13 + R15 (2x22R) parallel and pin1+2 (heater1) and pin 6+7 (heater2)to heater supply (5 VDC). The ends of POTI 1 remain between f1 and f4 and the adjustable pin of POTI 1 is connected to TP1 though R14 (150R). Please confirm that I understand well your words.

Regards, Gabor
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Re: LE-300BXLS-SE

Postby J. Leven » Wed Mar 13, 2013 8:11 am

Hi Gabor,
the driver circuit in the link:
the THD says nothing about the composition, k2, k3, k4, k5 etc .
The composition of the distortion is critical, and not necessarily the amount.

The amplifier has a very little feedback, 3 dB, of course you can make it switchable, but a soldered connection is better .

EML 300B-XLS-V4's: pin 8, the center tap (cathode) is connected directly to TP1, remove R13 + R15, pin1+2 (heater1)=f1 and pin 6+7 (heater2)=f4 to heater supply 5 V AC
The ends of POTI 1 remain between f1 and f4 and the adjustable pin of POTI 1 is connected to TP1 though R14 (150R).

J.L.
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Re: LE-300BXLS-SE

Postby hlcs25 » Wed Mar 13, 2013 7:23 pm

Hi J.L.

Thanks for your kind help and infos. What is your suggestion for resistor type i.e. canbon composition, carbon film, metal film or else?

Thanks in advance.

Gabor
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Re: LE-300BXLS-SE

Postby J. Leven » Thu Mar 14, 2013 8:08 am

Hi Gabor,
metal film, metal oxide is a good choice ,
C2, C1 and C3, C xx at power supply, have a greater impact than the resistor type,

Please note change ,at TP2, page 1:
R10 10K to 15K
Trimmer 10K to 5k

Best regards from Germany
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Re: LE-300BXLS-SE

Postby hlcs25 » Thu Mar 14, 2013 12:57 pm

Hi J.L.

Thanks for the corrections. I am searching for an available source of metal film resistors 1% 2W on the net in Europe but up till now I haven't been successful. Do you have any idea?

I have ASC 40uF/440VAC (800VDC) capacitors and I think they can be used in the PS instead of electrolytic ones. Do you agree with me?

Kind regards, Gabor
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Re: LE-300BXLS-SE

Postby J. Leven » Thu Mar 14, 2013 6:13 pm

Hi Gabor,
for R1, R2, R11, you can use 0.25 W-types,such as Vishay-Dale CMF55-143,
http://www.hifituning24.de//passive_bau ... /index.php
the 2 watt types have stronger wires and therefore it is easy and safe to soldered them to the sockets ,
you can use 5 % Resistor, there is no advantage in use 1% types at this point,
the circuit is constructed, that tolerances of the resistors have any impact.
The possibility of setting at TP2 balances all tolerances at this important point .

Power supply : the capacitor after D1,D2 should safe work to 650 V DC ,
your ASC 40uF/440VAC (800VDC)
the disadvantage is, the power supply will get bigger and bigger
look here,also used in industry amp :
http://www.reichelt.de/Elkos-radial/RAD ... +100%2F400
small size,

J.L.
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