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source amplifier, as a gate-source-drain amplifier or GSD for short. The advantage to such a system is that, like the periodic table of elements, the holes are readily apparent, which prompts us to fill in the blanks.
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impedance of about 10 k and a mu of about 8 when used in this way.
Simon B.
Brighton, UNITED KINGDOM
Thanks for the information. Battery tubes are definitely worth looking into. There a whole group of vacuum tubes designed for use in car radios that use the car's battery to supply both the heater voltage and the plate voltage! The 12DS7 and the 12DZ6 are capable of putting out a huge amount of current with only 10 volts on their plates.
The reason I avoided these tubes was to keep the tube sourcing easy. Which was something of a mistake, as special tasks require special tubes.
Subject: 6N3P preamp,
do you have some advice?
Thanks for a great webzine and great software! Recently I bought your Tube CAD program from Antique Electronic Supply and I have been playing with it for a while. From a sale I acquired several tubes from the former USSR including the 6N3P and I would like to design a simple line-level preamp with these. I was thinking of a constant current ground cathode amplifier and I have come up with the following part values (see schematic on next page). Two prototypes which I have made seem to perform well (when tested with sine and square waves and looking at the output on a scope). Even a 100 kHz square wave (4 Vpp output) looks good. But I have not yet performed listening tests as the dedicated PSU is not finished. My 6N3P tubes seem to have tight tolerances. They show almost identical measurements and they aren't microphonic. Maybe they were meant for the military. Current draw of the preamp is about 4 mA/channel. Measured voltage gain 25.3 (channel 1) and 25.8 (channel 2).
Do you have any suggestions or advice? Should I bypass the electrolytic cap with polystyrenes, for example? Forgive me for bothering you, I was just wondering if I had
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