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Old 11th May 2010, 01:32 AM   #1
rjm is offline rjm  Japan
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Default Advice sought on medium power triode for tube headphone amplifier

I'd like to build a "mini" tupe amp as a headphone amplifier for low impedance cans (16 ohms). Same transformer coupled circuit as your typical single-ended amp, just less power output... 250 mW into 16 ohms would be fine.

I already have the power transformer and choke, and these limit my total circuit current to 60 mA total over both channels. i.e. puts a 25 mA max realistic upper limit for the output tubes. The lower limit is defined by the design power output, say 250 mW, 16 Ohm load, ... figure a 10:1 winding ratio, ... giving very rough guestimate of at least 12 mA. 250 mW is quite arbitrary. 100 mW or even 50 mW of clean power would be more than sufficient to drive the headphones, so 5-10 mA is still on the table.

Anyhow, I am thinking along the lines of a triode connected EL84, but this is usually specified for about 40 mA of plate current in triode mode. Something a little more petite is called for.

Is there a nice option out there for a plate current of 10-15 mA and output impedance of 3000-6000 ohms?
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Old 11th May 2010, 05:07 AM   #2
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The 6N6P is used in the Little Dot HP amp, so maybe worth a look. Bonus is that it is a dual triode.
Triode connected 6AQ5 might be doable below 20mA, but it's hard to tell what the linearity will be like so near the bottom of the characteristic curves.
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Old 11th May 2010, 05:32 AM   #3
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6sn7 looks about right...

Kenneth
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Old 11th May 2010, 07:46 AM   #4
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How about the 46? Run as triodes they are linear and can sound very good. If you run them at book op. point of 22mA. they'll come in under your spec'd Rp and still leave you enough headroom for decent driver current . . .
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Old 11th May 2010, 11:44 AM   #5
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Quote:
Originally Posted by Hearinspace View Post
How about the 46? Run as triodes they are linear and can sound very good. If you run them at book op. point of 22mA. they'll come in under your spec'd Rp and still leave you enough headroom for decent driver current . . .
HI !
I think i would use the 12B4A ! They have a very nice sound! it is a very good double triode! it worth a test
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Old 11th May 2010, 03:28 PM   #6
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The 46 and 12B4 are good suggestions. I will add the 7119/7044.
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Old 11th May 2010, 03:38 PM   #7
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Hi !
I used for my headphone amp paralleled ECC804 (1 for each channel) and it works perfect!
I had surplus ECC804 and was wondering what to do them.....
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Old 11th May 2010, 03:39 PM   #8
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I have been planning a similar OT-coupled headphone amp, though with a 9:1 stepdown ratio. I will be using triode-wired C3m's, around 140V at 14-18ma, Zout around 2000 ohms into Lundahl 1689/18ma transformers (i.e. gapped for 18ma of primary quiescent current).

jacmusic.com (under NOS tubes and pentodes) has a link to the comprehensive datasheet and some more info. about them.

Also, any of the input tubes Lynn Olson describes for his amplifiers (Amity, et. al) would be candidates (JJ ECC99, 7119, etc.).

Good luck!
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Old 11th May 2010, 06:40 PM   #9
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To the C3M add the C3G (6.3V heaters, very delicate frame grid construction) at 160-180V at about 16mA.
These sound very nice (built two headphone amps with them).
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Old 11th May 2010, 09:36 PM   #10
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I am still working on a 6SN7 x2 headphone amp. My UTC outputs have 15K primaries and 50 to 500Ω secondaries. I still need to build a good very low noise power supply...those OTs pick up the slightest noise from fluorescent ballasts and power transformers. But I second the opinion of 6SN7s for your headphone amp. This is what I based my design on:
HeadWize - Project: The SESS Tube Headphone Amplifier by Andrea Ciuffoli

Kyle
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