Would it work:
A not half bad "amp" which has-
1) single 12ax7 with one triode as pre amp.
2) other triode as a sub 1w class A power amplifier.
Also:
1) I have read that 12ax7 being a pre- amp tube, would have high gain and introduce distortion as a power amp but im ok with a one-trick (but most metal) pony.
2) i posted this here (and not Instr. and Amps forum) because the tube is the whole amp. And that im new here.
Thanks.
A not half bad "amp" which has-
1) single 12ax7 with one triode as pre amp.
2) other triode as a sub 1w class A power amplifier.
Also:
1) I have read that 12ax7 being a pre- amp tube, would have high gain and introduce distortion as a power amp but im ok with a one-trick (but most metal) pony.
2) i posted this here (and not Instr. and Amps forum) because the tube is the whole amp. And that im new here.
Thanks.
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Tube data sheets show all the important parameters, along with plate dissipation in watts.
jeff
12AX7 is a POOR choice for a power amplifier.
WAY less than 1W available, and impossibly high impedance OT
WAY less than 1W available, and impossibly high impedance OT
2ma bias current, might be able to drive headphones to 50 mw with a 50:1 step down output transformer
Don't listen to all these naysayers on here, of course you can make a sub 1W power amp with one 12AX7, you don't even need one per channel if you have a source voltage at about redbook levels!
We will run the book operating point of 250V on the plate and 1.2mA of current. Plate impedance is only 62,000 ohms there. So you need a 200K:8 ohm output transformer gapped for 1.2mA of current. That will get you about 0.060W RMS into an 8 ohm load.
I don't know where you will find a 200K:8 ohm output transformer and I don't know what you'll do with 60mW, but you certainly could do this.
We will run the book operating point of 250V on the plate and 1.2mA of current. Plate impedance is only 62,000 ohms there. So you need a 200K:8 ohm output transformer gapped for 1.2mA of current. That will get you about 0.060W RMS into an 8 ohm load.
I don't know where you will find a 200K:8 ohm output transformer and I don't know what you'll do with 60mW, but you certainly could do this.
Most such designs follow the tube with something Solid-State, to provide power / drive into headphones or a speaker. The SS power section can be designed to have no character of its own, compared to the tube. So it's still "tube sound" as a selling point -
You may not know the trick of wiring the two triode sections in parallel, which creates (from what I've read here) a distortion generator. 2nd harmonic that is. Such an architecture - followed by some clean SS amp - may work out better than what you're currently thinking and make use of both triodes in the 12AX7 glass envelope.
Have a look at a Aune T1 to see how they successfully shoved a tube in between a DAC and a SS headphone amplifier. I assume your idea is mono vs stereo, but it maybe - conceptually - be just like replacing the DAC chip with a 1/4" input jack for your guitar. FWIW, I've never found the schematic for a Aune T1. Folks have gone NuTzO with the tube rolling in that thing, to get different sound qualities out of it. Maybe people would be just as crazed over your idea / product -
You may not know the trick of wiring the two triode sections in parallel, which creates (from what I've read here) a distortion generator. 2nd harmonic that is. Such an architecture - followed by some clean SS amp - may work out better than what you're currently thinking and make use of both triodes in the 12AX7 glass envelope.
Have a look at a Aune T1 to see how they successfully shoved a tube in between a DAC and a SS headphone amplifier. I assume your idea is mono vs stereo, but it maybe - conceptually - be just like replacing the DAC chip with a 1/4" input jack for your guitar. FWIW, I've never found the schematic for a Aune T1. Folks have gone NuTzO with the tube rolling in that thing, to get different sound qualities out of it. Maybe people would be just as crazed over your idea / product -
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OK, so you're really asking about flea power guitar amps, but wanted more of a Tube subforum response than an I&A subforum response.
The guitar flea power amps don't use a 12AX7 for reasons pointed out in the above responses. They typically use a 12AU7 in the output position. Even a 12AU7 needs a 12K or so OPT and is low power.
The guitar flea power amps don't use a 12AX7 for reasons pointed out in the above responses. They typically use a 12AU7 in the output position. Even a 12AU7 needs a 12K or so OPT and is low power.
6EA7/6EM7 will do what you propose, all in one bottle. Don't use a Hammond 125E OPT as I did, this was built before Hammond had modern small SE OPTs in their product line. But it makes an honest 2+ watts of audio.🙂
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6LU8 SE or UL Complete With Measrement Data
6LU8 has a Pd of 14 Watts vs 12 Watts for the 6T9. A little more power or better reliability. And it can be operated at higher voltages. Did this one early in 2002 as an experimental project. Not to look at.🙂
6LU8 has a Pd of 14 Watts vs 12 Watts for the 6T9. A little more power or better reliability. And it can be operated at higher voltages. Did this one early in 2002 as an experimental project. Not to look at.🙂
12AU7 is similar to the 6SN7. The 6SN7 can dissipate more plate power. I did a whole series of measurements on 6SN7s & similarly based double triodes last year, the 6SN7 in PP Class A barely exceeds One Watt. The 12AU7 in SE might be a problem at One Watt.
The plate supply was 300V, the load 27K plate to plate.🙂
Attachments
OMG read his post, he's asking about flea power guitar amps, stop with the hifi amp suggestions, your recommendations won't have appropriate gain amongst other issues.
From Post #2
Originally Posted by TubeEnthusiast
Would it work:
2) other triode as a 2-5w class A power amplifier.
Where did that 2-5W Class A Pwr Amp come from?😱
Thought we were responding to that.
Originally Posted by TubeEnthusiast
Would it work:
2) other triode as a 2-5w class A power amplifier.
Where did that 2-5W Class A Pwr Amp come from?😱
Thought we were responding to that.
What would be the consequences of bridging tube outputs vs using PSE tubes with a combined lower impedance, other than the obvious need for additional OTs?
He's asking about guitar amps. See the references to "metal" and the I&A subforum.
You can't make a guitar amp to drive a speaker with 1 12AX7 as the only amplifying device. You need to compromise and allow solid state devices, a different tube and/or additional tubes. And using just 1 tube will hardly save you money when you start adding in the cost of everything else. Back up and state what you are really trying to achieve.
You can't make a guitar amp to drive a speaker with 1 12AX7 as the only amplifying device. You need to compromise and allow solid state devices, a different tube and/or additional tubes. And using just 1 tube will hardly save you money when you start adding in the cost of everything else. Back up and state what you are really trying to achieve.