I was thinking of using a 717A as a small signal amplifier, (I haven't worked with small signal pentodes) but gain depends a lot on the anode resistor. If I wanted high current I would need a low resistance and I would get low gain. If I wanted gain of 100 - 200 I would need a 100Kohm or higher resistor. It seems a perfect place for a DN2540 - LM334Z CCS (I haven't worked with CCSs either). Has anyone tried them together>
You can look at 6AK5s data sheet for curves.