DN2540 + LM317 Cascode CCS


I’m doing the DN2540 cascode with LM317 so that i can set the current to exactly what i want. In this case, it is to load the RCA 5691 red base tubes with just 1.2mA of current per tube. This should be sufficient for voltage gain from the Bufallo DAC into the BCF, more importantly, I can draw from the same B+ rails that powers the BCF.

With the previous MJE350/BC557C and LED version, I could not get the resistors for the B+ correct. Quite frustrating when this has worked for me before…

Schematic is the same as Figure 13c from Jung. Rset is 1k to give 1.25mA.


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