by erichayes » Sun Mar 28, 2004 11:08 pm
Hi All,
Actually, Shannon, we're both correct for the same reason. The first description of the 'A stated that it was audio-oriented due to its controlled hum and microphonic characteristics. The original 'AX7, introduced in 1947, was considered an all purpose dual triode to be used in AF amplification, multivibrator (clock) and oscillator circuitry. When the Hi-Fi manufacturers adopted it as their quintessential voltage amp. tube in the '50s, RCA changed the heater design to lower the hum and noise (it runs at a lower temperature) and taunted it as the audio 12AX7 in 1960. When they discontinued the 'AX7 a couple of years later, the 'A was referred to as strictly an audio tube, and the 7025 (introduced at the same time as the 'A) became the upgrade of the 'A.
I swear, the 12AX7 and all of its mutant cousins probably has more mystique in its history than any other low level audio tube.
As I said, I'll be posting EpIp curve families for as many different 12AX7 brands as I can in the near (I hope) future, and the brethren can draw their own conclusions on sonic vs electrical characteristics. Should be fun.
Eric in the Jefferson State