Low voltage 12AU7 (19J6) -- re "starving" - Page 2 - diyAudio
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Old 5th May 2011, 05:09 PM   #11
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Here's what I'm driving at -- gain is just a hair under 20dB. THDsims out 0.015% @1V out. The resistor R8 represents the heater impedance of the 20EZ7 high mu triode. I adjusted the Leach coefficients until I got something resembling the 20EZ7.
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Old 25th January 2013, 07:22 PM   #12
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Little bit different -- a 1N4148 was used to bias the tube, and an LND150 Depletion Mosfet was used as a current source. I built one and tested it out:

Click the image to open in full size.

I'll call it the "Ascetic Student" as it's starving but dignified.
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Old 25th January 2013, 08:20 PM   #13
Cassiel is offline Cassiel  Libya
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Quote:
I'll call it the "Ascetic Student" as it's starving but dignified.
I don't know, it doesn't sound good to me. Starving but dignified belongs more to the 'artistic' family. An ascetic would never say 'I'm starving' (too proud for that) whereas artist and students have no problem declaring themselves so. Besides, ascetics are more masters than students.

Another point to have in mind is that an ascetic would probably have no need for a tube preamp.
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Old 26th January 2013, 01:46 AM   #14
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I use the term "ascetic" as a human being having a humble opinion of themself, a sense of simplicity and yet maintaining a sense of dignity.

I also have the image of a carving of an asectic monk, one so starved that the ribs protruded.
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Old 26th January 2013, 03:27 AM   #15
Cassiel is offline Cassiel  Libya
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I don't think ascetics have a humble opinion of themselves but it's true they're skinny. The 'starving' tag, nah, they wouldn't like it. An ascetic would look you in the eye and smile, knowing he's well fed. Spiritual richness makes you pretty wide.

Of course this has nothing to do with the name of your amp (it's your call).
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Old 26th January 2013, 06:34 PM   #16
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Quote:
Originally Posted by DF96 View Post
If you are very patient 19J6 appear on ebay from time to time, but who wants to wait a year before building an amp?
19J6 is the same as the 6J6/ECC91 tube, of course besides the heater, isn't it? You can buy the latter one for less than 5 in Europe!

Best regards!
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Old 26th January 2013, 07:07 PM   #17
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The resistance of the 19J6 is used to load the Mosfet. 19v @about 150ma is about 130 ohms.
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Old 27th January 2013, 12:45 PM   #18
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the 19J6 takes 18.9V @0.15A = 126 ohms. the 20EZ7 it 20V @0.10A = 200 ohms. Resistance is very low at turn on.
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Old 29th January 2013, 07:07 PM   #19
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Made a couple of changes -- R1 =55k, R5 = 2k2, R3 =110k. Did away with the CCS. The output cap is an Elna Silk 220uF/50V, the coupling cap that shown in the design 0f 100nF.

Changing R3 biased up the MOSFET a bit higher, while loading the amplifier a bit more. Gain is 19dB. The 5% THD is ~5V out.

Click the image to open in full size.

The above is with the 20EZ7 -- filament voltage is spot on at 20V.
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Old 29th January 2013, 07:36 PM   #20
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I looked into the 20EZ7 when I was designing a low cost guitar amp using a series string heater circuit. Although the 20EZ7 can sometimes be found for under $10 it is rather rare and was used in a few vintage guitar amps so it will disappear like the 19J6 as soon as someone starts using it in a published circuit.
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