Have never done anything with tubes but I am intrigued about the "sound" of tubes. I was thinking about a simple tube pre-amp to an LM3875 chipamp.
I came across this low-voltage tube 512AX
CK512AX
Pinout: 1(red dot)=anode, 2=screen, 3=filament, 4=g1, 5=filament Vf=0.625V, If=20mA. Va max=45V, Vsg=45V. No power limitation, since you can't draw enough current to do anything bad.
Pentode mode: gm=160uS. Triode mode:gm=250uS, Ra=35k, MU=9.
Reasonable amplifier bias points:
Pentode: 0.7V bias. Va=22.5V, Vsg=27V, Anode supply=45V. anode resistor=180k. Ia=.12mA, Isg=.06mA.
Triode: 0.6V bias. Va+sg=22.5V, Anode supply=45V, load resistor=100k, Ia+sg=.2mA.
Could this be simply implemented with 25V transformers? Are there other simple miniature or low-voltage tubes that would sound good? Since this would be a preamp, a lotta gain is not important or even preferred.
Thanks!
I came across this low-voltage tube 512AX
CK512AX
Pinout: 1(red dot)=anode, 2=screen, 3=filament, 4=g1, 5=filament Vf=0.625V, If=20mA. Va max=45V, Vsg=45V. No power limitation, since you can't draw enough current to do anything bad.
Pentode mode: gm=160uS. Triode mode:gm=250uS, Ra=35k, MU=9.
Reasonable amplifier bias points:
Pentode: 0.7V bias. Va=22.5V, Vsg=27V, Anode supply=45V. anode resistor=180k. Ia=.12mA, Isg=.06mA.
Triode: 0.6V bias. Va+sg=22.5V, Anode supply=45V, load resistor=100k, Ia+sg=.2mA.
Could this be simply implemented with 25V transformers? Are there other simple miniature or low-voltage tubes that would sound good? Since this would be a preamp, a lotta gain is not important or even preferred.
Thanks!
Wavelength Audio (Gordon Rankin) made an expensive preamplifier with the 6GM8 tube. I think is a good option.
http://www.wavelengthaudio.com/preamps.html
best regards Jaime
http://www.wavelengthaudio.com/preamps.html
best regards Jaime
Low Voltage Aikido preamp
OK, maybe not quite as simple, but you can build an Aikido preamp with the 6GM8 / ECC86, B+ voltage can be as low as 24V: http://www.tubecad.com/2006/04/blog0059.htm
As a benefit you can get superb PCBs from John Broskie at a reasonable price.
OK, maybe not quite as simple, but you can build an Aikido preamp with the 6GM8 / ECC86, B+ voltage can be as low as 24V: http://www.tubecad.com/2006/04/blog0059.htm
As a benefit you can get superb PCBs from John Broskie at a reasonable price.
Hi CarlosT,
What is your intention of the tube pre? do you need some gain or just a tube buffer?
Ecc88, 6922 can do at fairly low plate voltage of about 90V, low enough Rp to give low enough Zo, with a suitable plate choke, I think you can use ~100V B+ for the whole stage.
6AS7 or 6080 can also work in the 40~60 B+ zone... cathode follower if you must have that super low output mpedence, even with normal ground cathode, the impedance would still low enough for most applications.
6GM8 is good candidate, but From my experiments, I think the current is too small to produce good sounding cathode follower... I've not tried other method...
Cheers
What is your intention of the tube pre? do you need some gain or just a tube buffer?
Ecc88, 6922 can do at fairly low plate voltage of about 90V, low enough Rp to give low enough Zo, with a suitable plate choke, I think you can use ~100V B+ for the whole stage.
6AS7 or 6080 can also work in the 40~60 B+ zone... cathode follower if you must have that super low output mpedence, even with normal ground cathode, the impedance would still low enough for most applications.
6GM8 is good candidate, but From my experiments, I think the current is too small to produce good sounding cathode follower... I've not tried other method...
Cheers
WOW! So much to learn...so little time
That Aikido stuff was cool...as was the blog.
I got a buncha 25V + 25V toroidal trannies around so that's why I was thinking about low voltage tubes. I also currently have a combined channel mono LM3875 design which coulda benefitted from a buffer.
That Aikido stuff was cool...as was the blog.
I got a buncha 25V + 25V toroidal trannies around so that's why I was thinking about low voltage tubes. I also currently have a combined channel mono LM3875 design which coulda benefitted from a buffer.
Dang you guys! This stuff is SOOO tempting!
Could someone elaborate on the two outputs of the Aikido pre? Could a similar circuit be used with just one tube per channel?
A schematic for mm phono also would be great.
Thinking about building one as a gift to my brother in law.
Thanks!
Could someone elaborate on the two outputs of the Aikido pre? Could a similar circuit be used with just one tube per channel?
A schematic for mm phono also would be great.
Thinking about building one as a gift to my brother in law.
Thanks!
davidlzimmer said:Dang you guys! This stuff is SOOO tempting!
Could someone elaborate on the two outputs of the Aikido pre? Could a similar circuit be used with just one tube per channel?
A schematic for mm phono also would be great.
Thinking about building one as a gift to my brother in law.
Thanks!
Not one tube per channel, but you can use a single section on the input side - so three dual triodes total for two channels.
http://www.tubecad.com/2004/blog0013.htm
Sheldon
davidlzimmer said:Thanks, but I was wanting to stick with the 6GM8.
Broskie's three triode input example applies to any triode - either for the first or second position. The only requirement is that the triodes in the second position be identical to one another. If two triodes sections are used in the first position, they also need to be identical to one another. The point was that you can build a full Aikido amp with three triodes. I believe 6GM8 is a dual triode with identical sections, so it should work for either or both positions. And you can use three tubes total for a stereo pre-amp.
Sheldon
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