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?
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?
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.
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.
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
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.....
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.....
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!
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!
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).
These sound very nice (built two headphone amps with them).
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
HeadWize - Project: The SESS Tube Headphone Amplifier by Andrea Ciuffoli
Kyle
RJM,
Reconfigure your 'Twilight' circuit as 6H30 mu-follower, about 20-25mA with about 80V on the plate and about -3V of bias. Ditch your R5 and run all of the current through the tube. Parallel feed output (AC coupled) through Sowter 8665 wired 12:1.
Just one stage. (i.e. no separate input stage required).
If the Sowters are too expensive use Hammond 119DA.
If you are looking to drive 16 ohm In-Ear-Monitors then 5 mW will usually blow your head apart.
Reconfigure your 'Twilight' circuit as 6H30 mu-follower, about 20-25mA with about 80V on the plate and about -3V of bias. Ditch your R5 and run all of the current through the tube. Parallel feed output (AC coupled) through Sowter 8665 wired 12:1.
Just one stage. (i.e. no separate input stage required).
If the Sowters are too expensive use Hammond 119DA.
If you are looking to drive 16 ohm In-Ear-Monitors then 5 mW will usually blow your head apart.
I used a WE417A, but for 32 / 300 ohm switchable.
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Thanks for all the excellent suggestions. Really good.
By the way, the output transformers I'm looking at are the following:
Noguchi FM-3WS-H
It also comes in medium and low inductance windings with greater current capacity, but given the current contraints involved with the power supply I'm going to use I might as well go with the high impedance version... so I'm looking at 14k primary impedance.
By the way, the output transformers I'm looking at are the following:
Noguchi FM-3WS-H
It also comes in medium and low inductance windings with greater current capacity, but given the current contraints involved with the power supply I'm going to use I might as well go with the high impedance version... so I'm looking at 14k primary impedance.
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Hello rjm,
I have tried several tubes as headphone SET amplifiers; the 12B4 already discussed, 6BX7GT, 12au7 and 6SN7. I liked the 12B4 and 6BX7 better because of the lower plate resistance coupled through the output transformer makes for lower output impedance and less flabby bass.
The thing to keep in mind is that headphones require very little power or voltage swing to operate. At the low power output there is very low distortion. So if you select an operating point nearer the knee of the plate curves the amplifier will sound more like a Single End Triode. I am not saying a lot of distortion, less than 0.25% at the maximum power you would want on your head.
The tube I have come to like best is the 6BQ6GTB but it is idling at 40 ma which is more than your power supply will allow. The power transformer I am using is a Triad N-68X isolation transformer at about $12 US (cheep). 180 volts at 40 ma per tube.
DT
All Just For Fun
I have tried several tubes as headphone SET amplifiers; the 12B4 already discussed, 6BX7GT, 12au7 and 6SN7. I liked the 12B4 and 6BX7 better because of the lower plate resistance coupled through the output transformer makes for lower output impedance and less flabby bass.
The thing to keep in mind is that headphones require very little power or voltage swing to operate. At the low power output there is very low distortion. So if you select an operating point nearer the knee of the plate curves the amplifier will sound more like a Single End Triode. I am not saying a lot of distortion, less than 0.25% at the maximum power you would want on your head.
The tube I have come to like best is the 6BQ6GTB but it is idling at 40 ma which is more than your power supply will allow. The power transformer I am using is a Triad N-68X isolation transformer at about $12 US (cheep). 180 volts at 40 ma per tube.
DT
All Just For Fun
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