What are some good tubes to swap for a 12ax7 for microphone use ?

Omega757

Omega757

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Now that my mic is on the way i was wondering what are some good tubes to try out ? Any suggestions ? Anyone got some they are willing to donate? (WinK) :thumbs up:
 
Omega757 said:
Now that my mic is on the way i was wondering what are some good tubes to try out ? Any suggestions ? Anyone got some they are willing to donate? (WinK) :thumbs up:
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Are you talking about a valve for a capacitor mic or for a pre amp? Either way the 12AX7/ECC83 is a poor choice. Lazy design IMHO.
Dave.
 
Omega757 said:
Can you name any specifics ?
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No because I am firm believer in keeping the valve type that the orignal designer used. Be this a mic pre amp or guitar amplifier.
The E88CC is for instance a very good audio valve but unless the anode loads and bias components are changed for the correct value it is liable to just sound worse than the proper valve and might cause circuit damage.

If the orignal is an ECC83/12AX7 then the TAD 7025 high grade is a very good valve at a fair price (and exact replacement). Buy a few and select for best performance.



Dave.
 
OP please be more specific about the mic. A lot of times a 12AX7 is put into a microphone because they are cheap and the mic may even be really designed for something with less gain, like a 12AT7 or a 12AY7. They are all reasonably close in design paramaters and people do swap out without changing plate/cathode resistor.

Depending on the mic, a 12AY7 would be worth trying out. Get a new one, they are about US$15.00. What are you hoping to accomplish by changing tubes? A 12AX7 hand rolled in 1954 by the hands of New Jersey... well, you get the point, may not be the change you are looking for.

Edit: I'm not contradicting ecc83 here, the 12A?7's (I am more familiar with the American designations) are *pin compatible* have *similar* operating maximums and depending on the other parts it is *possible* to swap different ones. I've swapped, e.g. a 12AU7/12AV7 & 12AX7 in a preamp designed for a 12AX7 for different tones, without consideration to wear on the tube. The stock circuit distorts like crazy, the 12AU7 just enough gain to be just enough, and I really want to try the 12DW7 and the reverse one (ECC832?)
 
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No offense taken Blue!

My cautioin is simply because it IS possible to burn out very wee anode loads. I have some numbers somewhere that show fitting an A7 in place of an X7 pushes the anode load dissipation up to close to 1/2 watt and that is with, IIRC, a 290V supply. HTs get higher than that.

The A7 and X7 really do need different bias resistors to function linearly. I am not agin' people experimenting just don't blame the gear or the valves if it sounds ***t!

A big exception is the 12AU7 (ECC82) This is commonly used as a reverb tank driver with both sections paralleled, the other two triodes really cannot handle the power. It is also used as a low impedance driver to power valves in some amps "of my aquaintance" and anything else sounds dreadful and does not last long.

Dave.
 
ecc83 said:
No because I am firm believer in keeping the valve type that the orignal designer used. Be this a mic pre amp or guitar amplifier.
The E88CC is for instance a very good audio valve but unless the anode loads and bias components are changed for the correct value it is liable to just sound worse than the proper valve and might cause circuit damage.

If the orignal is an ECC83/12AX7 then the TAD 7025 high grade is a very good valve at a fair price (and exact replacement). Buy a few and select for best performance.



Dave.
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Well it's not the best tube mic in the world lol.But here is a pdf manual of it. I've read that most stock tubes are crap is why i'm looking to try some different ones. I saw some posts around the net where people were recommended different tubes for different flavors. Ex. Ameperex,RCA,Sylvania,Mullard,Telefunken,and so on.

Here's link to a review of it - You can see the specs in the Design and Construction section. CAD M9
 
Omega757 said:
Well it's not the best tube mic in the world lol.But here is a pdf manual of it. I've read that most stock tubes are crap is why i'm looking to try some different ones. I saw some posts around the net where people were recommended different tubes for different flavors. Ex. Amperex, RCA, Sylvania, Mullard, Telefunken, and so on. Here's link to a review of it - You can see the specs in the Design and Construction section. CAD M9
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I think the CAD M9 is a great really great tube mic.
It has a brightness to it with the stock tube that is pretty nice.
A Pair would be great for drum overheads.
The 7025 Tube will work just fine in place of a 12AX7 and will be less noisy.
I believe that the 7025 was built for medical and scientific equipment where a lower noise factor was required.
To tame the highs, you could do NOS Mullard but you are talking $$$
The current model 12AX7 Tung-Sols are not bad for a lower cost replacement for stock 12AX7.
I agree with sticking to the 12AX7 when the stock tube is a 12AX7 primarily because when you replace the 12AX7 with a tube with lower gain, (12AT7 etc.), you have increase gain elsewhere to make up the difference level-wise and when you simutaneously increase the gain to make up that difference, you also increase whatever noise that is inherent in the lower gain tube.
 
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