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You should be more specific and give more information.

Anyway I did a google search and the el34 & el84 are vacuum tubes, I wouldn't recommend valve circuit for newbs as you need high voltages and a separate heater power supply, In short no vacuum tube circuit is simple.

I googled again and found you some circuits:

Anyway unless you're building high quality audio amplifiers or high power radio transmitters valves suck major arse and have no place in modern electronics.

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...and, if it's good enough for AOpen, who am I to disagree??? ;)

"Today AOpen shows us something that, while it could be considered revolutionary, may also be very "old school" to many of our readers out there. AOpen is putting vacuum tubes back onto the desktop platform.

The pictures below are of the AOpen AX4B-533Tube. It's an i845E based board that supports both 400MHz and 533MHz bus Pentium 4 CPUs with DDR RAM up to PC2100 spec. The ICH4 hub is used with the i45E at this time which brings native USB 2.0 support to the board. While this board hosts a myriad of overclocker features, what's really the attention getter is the audio system on-board.

One of the greatest gripes about onboard sound today in the mainboard market is the quality of the sound. While there have been solid advancements and onboard sound has certainly grown leaps and bounds in the last year, AOpen wanted to come in and do it like no other company has.

While no full specs were yet available to us, AOpen has taken a lead from the high-end audio component producers and used a vacuum tube system on their mainboard which they say produces overall sound quality that cannot be duplicated on silicon.

The first picture shows the overall board layout. The sound components are clearly visible at the lower edge of the board. You might also notice only three PCI slots. AOpen has also included an onboard NIC on this board. Considering that, and the fact that anyone purchasing this board is very likely to use the onboard sound, AOpen sees three PCI slots as being plenty.

Close ups of the tube and other components show off that this isn't just for decoration. The header that you see in the second picture above is not a power header, but rather the plug that handles the audio out jacks.

You old guys will remember that vacuum tubes need some high-end power as well. And just who-the-heck is he calling old? AOpen has fitted the board with components spec'ed at twice the 200 volt power requirement by the tube system in order to produce a solid and stable platform. Seems to be no skimping here.

The last picture shows the AX4B-533Tube running an audio system in the AOpen booth, and from what we heard, their tube board seems to be just what the audiophile may be looking for. Another interesting software feature that will be shipped with the board is CD Player software. While this does not seem to be anything new, AOpen's solution can run the CD player without booting into a Windows OS. The CD Player loads immediately after the BIOS."


Credited to: HardOCP.com, Monday, June 3, 2002

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Yeah, audio fanatics like the 2nd harmonic distortion and the soft clipping from tube amps.
Notice the Aopen tubes? Their stamping looks like they were made in Russia in 1969. They will need replacement, what if there are none remaining? Chinese tubes? Remember when even the food store had a tube-tester? The manufacturers probably made the tubes have a short life so you would have to buy more.
I made an amp back then using a pair of EL34's for its push-pull outputs. I could never keep them matched. A hi-fi store offered a free amp analysis clinic to show how much better their new amps were. I was shocked when they measured 12% distortion and nowhere near the rated power output from my amp! :o ::) ;D

AM transmitter? The first time I heard the good quality of FM I never listened to lousy-sounding AM anymore. I can't remember the number of tubes in the FM tuner that I built, it and the amp kept my room nice and warm. I still have my very first transistor project: an FM transmitter. Then I tried a tunnel diode, remember them?

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