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Old 22nd April 2013, 10:36 AM   #1
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Default 6sn7 mu-follower

How can change the ECC81 mu-follower to use 6SN7? Wich gain will be with 6SN7?

TIA
Felipe
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Old 22nd April 2013, 11:13 AM   #2
DF96 is offline DF96  England
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Voltage gain will be approximately equal to mu for the lower valve.

To change from ECC81 to 6SN7 you need to choose new operating points and calculate new component values. Or find and copy an existing design.
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Old 22nd April 2013, 11:19 AM   #3
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Thanks for help....
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Old 22nd April 2013, 11:29 AM   #4
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Old 22nd April 2013, 12:42 PM   #5
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What about this schematic Ian aka Ruffrecords suggested?
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Old 22nd April 2013, 12:54 PM   #6
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Hi!

Without some more information what you want to do and why you think a mu follower is a good idea for your application, nobody will be able to give good advice.

Also why not just try the configurations you digged up and report your findings?

Thomas
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Old 22nd April 2013, 01:03 PM   #7
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Hi,

Don't interested in the last posted schematic because have an output impedance of 1500 ohms & I need 300 ohms or less to use as headphone amp for my Sennhs HD600

Felipe
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Old 22nd April 2013, 01:18 PM   #8
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Hi!

300 Ohms is very low. Do you really want to use a mu-follower for that?
You will need a huge coupling cap. 100uF already has an impedance of 80 Ohms at 20Hz.
Even if you accept a higher roll of frequency, you'd still need at least 50uF

Thomas
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Old 22nd April 2013, 02:15 PM   #9
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Thanks Thomas, I'm exploring other OTL alternatives.
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Old 22nd April 2013, 03:30 PM   #10
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Quote:
Originally Posted by merlin el mago View Post
Thanks Thomas, I'm exploring other OTL alternatives.
You will not be able to drive 80 ohms phones to reasonable levels using a single tube like the 6SN7 or ECC88 in an OTL configuration. To output 10mW into an 80 ohm load requires a peak current of nearly 16mA which means the idle current of an OTL stage has to be at least this value. The thing is you only need a voltage of 900mV so you are asking a tube to produce a high current at a low voltage, exactly the opposite of what it does well. The answer is a transformer and with a suitable turns ration an ECC88 will happily drive a pair of 80 ohms phones to high levels at low distortion and with plenty of headroom.

Cheers

Ian
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