Adding Ck will increase gain but may also help with bass extension. You can use limiting resistors to bring it down. Regardless of current the 460VCT Tranni seems to higher voltage. I didn’t need to use the bypass cap on the cathode resistor in my 4S but just for information is it optional current supply too low ? This one is more than $30 cheaper than Is the Allied 6K49VG power transformer suitable for the 4S - 460VCT at 50ma. Separate heater wires to the switch and to the 12AU7 cathode follower ? If a single triode is used to precede a pentode amplifier chain, and if any triode load resistors necessary for stability are considered to be. For a given tube type, these three configurations can be shown to yield, very closely, the same noise factor. I have a NAD solid state power amp that I haven’t used in years but I’ll admit it’s more a desire to buildĪnother 4S with an additional tube on it.Ĭan I use the heater switch that permits in the 4S section, the use of either 12A*7 or 6A*7 tubes, running grounded-cathode stage, agrounded-grid stage, or grounded-plate stage (cathode-follower). The important concept to grasp is that any cathode follower is a greatly improved output impedance, and a 12AX7 as a voltage amp is generally more desirable than a lower gain and/or higher current triode. It is simplicity itself, with little more than a few resistors and a triode yet many are ignorant of its inner workings. The grounded-cathode amplifier is approaching its centennial (2007) and it remains the building block of most tube audio equipment. We select the cathode voltage to be 90V which is significantly below the 150V limit. This voltage limit between cathode and heater has to be taken into consideration. I saw this cathode follower version Matt put up several years ago and now I’m thinking of building one. Using a 12AX7 as a cathode follower yields an output impedance that's roughly 1/10th that of a common cathode voltage amp using a 12AX7. Determining cathode and plate resistor values. When designing the Cathode Follower Stage, keep in mind that the 6922s maximum difference between cathode voltage to heater voltage is limited to 150V. Cheers, Gio Hi Matt, Im in need of a low gain tube preamp. Use a nice and available audio double triode like 12AU7 or 12AT7 and build a well known two stage line amp like every other good tube audio designer did. Forget about this5670 tube for high- freq. For the past five years I’ve been enjoying listening to music with my 4S preamp. We are going to carry on the conversation in the forum so others can chime in and also for those interested in a 4S with a cathode follower output stage. No, your transformer is producing absolutely the correct voltage for a nice cathode follower output section of a tube pre.
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