Aikido Phono Amp Output Tubes 12AU7 and 12AX7? - diyAudio
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Old 26th April 2010, 02:37 PM   #1
JustinJ is offline JustinJ  United States
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Default Aikido Phono Amp Output Tubes 12AU7 and 12AX7?

Aikido Phono Amp Manual Page:

The manual is at the bottom of the page

At long last: the Aikido Phono Preamp

Aikido Phono Amp:

Aikido Phono Preamp Kit

I am needing help on choosing which tubes to pair up together. I am needing more gain since I am using a Denon Dl 160 Cartridge, which is rated at 1.6v.

I was thinking of the 12AX7 for the input stages V1, V3, V5, V7 but I am not sure what to use for the output tubes V2, V4, V6, V8. I see the 12AU7 and the 12AT7. I am not sure of which one to use.

I do need to use quiet tubes because of my speakers being Electrostats.

What are the differences in the 12AU7 and 12AT7?


P.S.

On a side note, I found an excellent electronics book at a local book sale. It was a copy of the book Electronics Made Simple 1965
Amazon.com: Electronics Made Simple (9780385012270): Henry Jacobowitz: Books

The book really delves into tube and discusses tube amps. I had some newer books but they really did not discuss tube in depth.
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Old 26th April 2010, 03:12 PM   #2
DougL is offline DougL  United States
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Here, try this:
Tube Data Sheet Locator

HTH

Doug
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Old 26th April 2010, 05:33 PM   #3
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The 12AU7 is lower gain (mu ~ 20) vs. 12AT7 (mu ~ 60). The 12AU7 has lower plate resistance compared to the 12AT7. The 12AT7 has about double the Gm. Lastly, they bias differently, just generally different tubes.

The output stage tubes are working as cathode followers (with a TubeCAD twist of course). I would say that a better suited tube for these stages would be either the 12AT7, if you use one of the above, or a 6922. You could also look for 6BK7's or 6BQ7's as they will work in these positions and also provide low output impedance. As a bonus they are cheap, ranging between $2.00 to $10.00 each for NOS examples.

12AX7's should work fine in the first positions if you need the gain. If you can find them reasonably priced, look for 7025's, the low-noise Hi-Fi 12AX7. 5751's may offer slightly lower noise being lower gain, but your phono amp will have less gain as well. There are other low noise 12AX7's out there, JJ ECC803s come to mind for new production. You could also try and track down CBS 7729's, though they seem to be exceedingly rare and pricey. I tracked down one NIB at a surplus store a couple of years ago by dumb luck, I have never seen another one.

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Old 26th April 2010, 08:54 PM   #4
JustinJ is offline JustinJ  United States
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Hello JPeitzman,

Thank you for the through response. As I am new to tubes it helps with understanding why I would choose a certain tube.

I will do a search and see if I can find some of the tubes you suggested.

Do you have any places online that has good prices on Tubes. I am little hesitant with EBay. Although, once I know what I am doing with tube amps, I will be scouring Ebay for some to try out with my amp. I try to stay away from Ebay because I usually will find something of interest.
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Old 26th April 2010, 09:33 PM   #5
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Some good places to start:
Antique Electronic Supply
Welcome to TubeDepot.com!
thetubestore.com Audio and vacuum tubes for your amplifier.
Angela Instruments Online Catalog - Home

The TubeDepot and The Tube Store I would use mostly for new stock, some of their NOS tubes seem a bit inflated. At the first three sites you can't always find your tubes in the broad categories, it's much easier just to type them in the search box.

Other good sites for some tubes (Nebraska Surplus) and for parts (all):
Surplus Sales of Nebraska
DigiKey Corp. | Electronic Components Distributor | United States Home Page
Mouser Electronics - Electronic Component Distributor
Allied Electronics ? Electronic Parts and Components Distributor

Hope this helps!
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Old 26th April 2010, 09:41 PM   #6
toufu is offline toufu  United States
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I just built the Aikido Phono Preamp. I used 6n1p for all 8 tubes, sounds good, just make sure you use Rk of 200-300. I also plugged in 6n2p's and that was good too, much higher gain than the 6n1p. And on top of that, 6n1p and 6n2p tubes are super cheap on Ebay.
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Old 26th April 2010, 10:04 PM   #7
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^^^Did you happen to re-bias or anything, or just plug them right in? The 6N2P is more akin to the 12AX7 and operates different from the 6N1P. The in 6N1P is more like a 6922, though it kind of wishes it was a 6922, the 6N23P is the better Russian 6922. If these tubes will work in this design I would look for 6N2P's for the front end and 6N1P's or better, 6N23P's for the outputs. They are cheap, you don't have to feel bad if you kill a few, and if you don't like them you don't have to feel bad tossing a $1 tube in the desk draw.
6N2P-EV / 12AX7 / ECC83 tube - Hi Fi audio tubes - Tubes-Store.com
^This is the high reliability military version selected for low noise
6N1P-EV / 6DJ8 / ECC88 / 6922 tube (own box) - Hi Fi audio tubes - Tubes-Store.com
^Military version with extended life
6N23P-EV / E88CC / 6DJ8 tube - Hi Fi audio tubes - Tubes-Store.com
^The better 6922 equivalent, again Military extended life.

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Old 26th April 2010, 10:19 PM   #8
toufu is offline toufu  United States
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No, I didn't rebias. I just plugged them in. I suppose I should make the Rk a higher value than 300 for the 6n2p to compensate for the higher gain, but I didn't want to resolder everything as I as pretty happy with the 6n1p sound. I think I might get some 6n23p's just to play with as I am happy with the other soviet tubes so far.
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Old 28th April 2010, 03:55 PM   #9
alexg is offline alexg  Philippines
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I have used 12at7 for input and 12au7 for output for an aikido phonostage.

I also have used 5751 input and 12au7 with great results.
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Old 28th April 2010, 08:57 PM   #10
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The thing to watch for in Russian tubes like the 6N1P is the heater current. It is twice the typical value for western equivalent tubes, so your heater supply needs to be big enough to cope.
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