Some lower cost tube microphones are built around the 12AX7. Others use the 12AY7 or even the 12AT7. Rick, what's the difference?







(originaly posted to old forum at an earlier date)

The 12AX7 is the most widely available tube in production these days and is therefore very easy to find. It is a high-mu twin triode with an amplification factor of 100 and has a maximum plate dissipation of 1.2 watts.

The 12AT7 is also a high-mu twin triode. It has less gain than the 12AX7 with an amplification factor of 60. Plate dissipation is twice as high at 2.5 watts. It makes a better driver tube and is a more logical choice to send a large signal into a low impedance. Since it is not mainly used in the front end of preamps, it is often more microphonic than a 12AX7.

The 12AY7 is a medium-mu twin triode with an amplification factor of 40 and maximum plate dissipation of 1.2 watts. It had become very rare but is now being produced again by Electro-Harmonix.

Also used in some designs is the EF86 penthode (Neumann U67) and the Nuvistor tube (eg. 6CW4). The Nuvistor utilizes a light-weight cantilever-supported cylindrical electrode structure housed in a ceramic-metal envelope. It combines newer materials, processes, and fabrication techniques and is much smaller than a miniature tube (0.8" high)



(originaly posted to old forum at an earlier date)

I might be out of line here but... Would a pentode valve be useful in an opto-compressor circuit?






(originaly posted to old forum at an earlier date)

Hi G-Prox, The penthode is commonly used in tube compressors.
A triode has only one controlling element, the input grid, to which the input signal is applied.
The penthode has an additional controlling element, the screen, which can be used as a gain control.
Addionally, the penthode has much higher gain than the triode which is ideal for a compressor circuit.



(originaly posted to old forum at an earlier date)