OTL tubes amplifier based on the ecl84 - diyAudio
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Old 26th April 2011, 11:42 PM   #1
00940 is offline 00940  Belgium
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Default OTL tubes amplifier based on the ecl84

Who said tubes amplifier had to be warm and lush ? This one certainly isn't I've got a prototype of this amplifier working on my bench and it has serious slam.

It is based on conventional building blocks: mu-follower for the gainstage, white cathode follower for the output stage. The little triode in the ecl84 has some serious gain, which compelled me to use a relatively heavy feedback to take the gain down. The trioded pentode sections are run pretty hard at 170V and 25ma each. The tubes aren't very expensive but I'll try to run the amp a bit colder in the long term (something like 160V, 23ma). Into a 300ohms load (headphones in mind are AKG K340, senn HD600), it translate into more than needed power.

All the coupling caps are mkp, resistors are a mix of 2W and 0.6W metal film, depending on position (and applied voltages).

Click the image to open in full size.

The power supply is coming straigth from tubecad's website, with a small twist to use 200V rated caps on a 380V supply. The heaters are biased somewhere around 90V. I use AC and it's silent (no hum) with high impedance headphones.

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Old 9th September 2011, 08:48 PM   #2
fbx is offline fbx  France
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Nice, indeed.
Does it give an acceptable power also down to 32 ohms?
Have you done measurements of the THD and its harmonic content?
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