Vacuum tube audio amplifier

Posted on Feb 6, 2014

Where can you obtain a 12AX7 tube, you ask These tubes are very popular for use in the `preamplifier` stages of many professional electric guitar amplifiers. Go to any good music store and you will find them available for a modest price ($12 US or less). A Russian manufacturer named Sovtek makes these tubes new, so you need not rely on

Vacuum tube audio amplifier
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"New-Old-Stock" (NOS) components left over from defunct American manufacturers. This model of tube was very popular in its day, and may be found in old "tubed" electronic test equipment (oscilloscopes, oscillators), if you happen to have access to such equipment. However, I strongly suggest buying a tube new rather than taking chances with tubes salvaged from antique equipment. It is important to select an electrolytic capacitor with sufficient working voltage (WVDC) to withstand the output of this amplifier`s power supply circuit (about 170 volts). I strongly recommend choosing a capacitor with a voltage rating well in excess of the expected operating voltage, so as to handle unexpected voltage surges or any other event that may tax the capacitor. I purchased the Radio Shack electrolytic capacitor assortment (catalog # 272-802), and it happened to contain two 47 µF, 250 WVDC capacitors. If you are not as fortunate, you may build this circuit using five capacitors, each rated at 50 WVDC, to substitute for one 250 WVDC unit: Bear in mind that the total capacitance for this five-capacitor network will be 1/5, or 20%, of each capacitor`s value. Also, to ensure even charging of capacitors in the network, be sure all capacitor values (in µF) and all resistor values are identical. An automotive ignition coil is a special-purpose high-voltage transformer used in car engines to produce tens of thousands of volts to "fire" the...

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