Low voltage tube RF preamplifier

by sv3ora



The biggest disadvantage when operating tubes on high voltages is not the high voltage PSU, this can be relatively easy to build. The biggest disadvantage is that most of the other components in the circuit must be also of high voltage. This increases the cost at a geometric rate, since one cannot use common modern low voltage components anymore. When the specific application you build, operates on  low signal handling, then it is perfectly fine to use low anode voltages in some stages and then use high voltage only when great amplification is needed and not throughout the whole circuit.

Here is a vacuum tube RF preamplifier I have designed and tested, which works fine with low anode voltage of 6V, just like the filaments of the tube. I have tested the preamplifier on 500KHz (IF) but I do not see why it should not work at many other frequencies. I included a 180 ohms cathode resistor and a capacitor across it, to prohibit the tube from working as a rectifier. The cathode to ground voltage should be somewhere between 100-200mV and in my case was 110mV.

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