[mewrei]

Sorry for the insanely simple question and further apologies if its in the wrong section, but I'm looking at building some headphone tube amps, namely the Millet MAX, but I'm looking at the tubes it requires, and I'm interested in experimenting some with the tubes it uses.

My question is, I know the unit can use things like the 12AE6 (or the 12AJ6, which might be preferable with the 600ohm Beyerdynamic BT880's I'm thinking about getting), which, if I'm understanding correctly, means its a 12 volt tube with 6 internal elements. Now this may be my experience with solid state components, but wouldn't the number of internal elements not be too important to the overall function of the unit itself?

If this is so, would a plausible replacement for the 12AE6 be a 12AX7 (assuming the pinouts are identical)?

If I'm wrong (or even if I'm right) would someone please explain a bit more about how the number of internal elements effects outcome? I've read the basics so I'm familiar with the difference between a tetrode, pentode, etc (I'm assuming the number of internal elements has to do with this but I'm not wondering how you can tell the difference between a tetrode and an audio beam tetrode, aside from reading the datasheet).

Thanks guys!

 

[Nemo de Monet]

Quote:

Originally Posted by mewrei /img/forum/go_quote.gif My question is, I know the unit can use things like the 12AE6 (or the 12AJ6, which might be preferable with the 600ohm Beyerdynamic BT880's I'm thinking about getting), which, if I'm understanding correctly, means its a 12 volt tube with 6 internal elements. Now this may be my experience with solid state components, but wouldn't the number of internal elements not be too important to the overall function of the unit itself?

Yes and no. If you understand the difference between, say, a triode and a pentode, then you'll realize that you can't have a twin triode, for example, with four internal elements, so in some circumstances you can use the number of elements to identify the general type of tube, which was probably somewhat helpful back in the days of tube radios and televisions.

But as a naming convention, which is all it really is, it's no more or less meaningful than anything else, like "E88CC" or "6N1" or "EL34".

Quote:

If this is so, would a plausible replacement for the 12AE6 be a 12AX7 (assuming the pinouts are identical)?

No, because it's not the number that's really important - more isn't better! It's what the tube does - the 12AX7 is a dual triode (two anodes, grids, cathodes, plus one heater == 7 elements), whereas the 12AE6 is a triode and two diodes in a single package (anode, grid, cathode, diode, diode, heater == 6 elements).

Even then, if you just compare the triode parts of each tube, they perform radically differently; read the datasheets. 12AX7s have a gain of around 100; the 12AE6 has a gain of around 14.

You aren't comparing apples and oranges; you're comparing bananas and watermelons.

Quote:

If I'm wrong (or even if I'm right) would someone please explain a bit more about how the number of internal elements effects outcome? I've read the basics so I'm familiar with the difference between a tetrode, pentode, etc (I'm assuming the number of internal elements has to do with this but I'm not wondering how you can tell the difference between a tetrode and an audio beam tetrode, aside from reading the datasheet). Thanks guys!

Mechanically, a tetrode is a tetrode is a tetrode. If you want to know what it does - or what it was marketed to do, which is not always the same thing! - read the datasheet. All the name tells you, with American tubes, is the heater voltage and the number of elements; trying to read anything more into it is almost certainly a recipe for disaster.

 

[mewrei]

Rock on man, thanks for the excellent information.

 

[Uncle Erik]

The number of elements is somewhat misleading in audio. Almost always, audio tubes are connected as triodes, even though the tube itself may be a pentode or something else. You need to look to the circuit to see how the designer is using it.

 

[tomb]

Don't dare use a 12AJ6, either! While technically, it will work in the tube circuit on a Millett MAX/MiniMAX, it WILL NOT WORK with the diamond buffer output stage (as in "Hybrid"). The same voltage supply for the amp supplies both the tube circuit and the output buffer stage. What that means is that the gain of a 12AJ6 tube will cause the tube's voltage swing to out-strip the voltage capability of the output buffer. IT WILL NOT WORK.

As for compatible tubes - 12AE6, 12FM6, 12FK6 - that's it. As the other guys have explained, other tubes will not work ... they don't even have the same number of pins.

 

[mewrei]

Good to know, thanks guys. Lesson learned, build the dang thing and don't mess with it

 

[Uncle Erik]

If you want to mess with other tubes, there are many, many other DIY designs out there. It's OK to have more than one amp.

Sorry about your wallet.

 

[00940]

Quote:

Originally Posted by Uncle Erik /img/forum/go_quote.gif The number of elements is somewhat misleading in audio. Almost always, audio tubes are connected as triodes, even though the tube itself may be a pentode or something else. You need to look to the circuit to see how the designer is using it.

Almost always ?

A bit strong of a statement. There is aplenty of audio gear using the pentodes as pentodes or in ultralinear mode. If triode strapping is indeed common, it is far from being the rule.

In gain stage, the extra gain of the pentodes is at times very useful.
In pushpull output stage, the extra power of the pentode mode is interesting.

 

[digger945]

diyAudio Forums - On Line Tube Learning for newbies.... - Page 1

Neets Module 06-Introduction to Electronic Emission, Tubes, and Power Supplies

 

[DKJones96]

The naming convention you are speaking of isn't perfect either. 2C26 - 6.3v transmitting single triode. Nowhere near 26 elements and not a 2v heater..

You use a pentode as a pentode in audio because if the ultra linearity you get from having the control grids, screen grids, and suppressor grids doing their intended jobs. Tetrodes are almost never used because of the unpredictability they offer in the AF band and triodes are generally used in hybrids because it makes the design easier and the tube is just being used as a pre-amp for a headphone amp. You don't need a 30watt power tube to drive 1/2 watt into some headphones.

In my new hybrid I went with triodes simply because two could be used in a single package and it reduced the cost of parts(the only reason I went with a solid state output stage to begin with since 200w tube output stages are very expensive).

 

[Uncle Erik]

Quote:

Originally Posted by 00940 /img/forum/go_quote.gif Almost always ? A bit strong of a statement. There is aplenty of audio gear using the pentodes as pentodes or in ultralinear mode. If triode strapping is indeed common, it is far from being the rule. In gain stage, the extra gain of the pentodes is at times very useful. In pushpull output stage, the extra power of the pentode mode is interesting.

You're right - I've been looking at too many headphone amps lately.