I finally got around to wiring this little firecracker into a single-stage amplifier ... sounds very good. I'm using 150VDC regulated supply feeding 5uF of film capacitance on the supply. To reduce the effect of power supply noise, I played around with various topologies, including WE cathode capacitor, using a transformer as a choke + attaching the secondary to the cathode (call it a WE cathode transformer), etc. These measures improved the sound, but left me unsatisfied. I also added inductance to the power supply (15H, 25H, 125H) but felt the inductor dulled the sound considerably. I then settled on wiring two tubes in parallel, feeding them with opposite phase inputs from an input transformer, powering them from the same supply, each with its own output transformer, and cross wiring the output transformer secondaries to the speaker (call it inverted, cross-wired parallel single ended). Lovely sound. Now to my question
Can someone pinpoint for me what I should look for on a scope to see if either of the tubes is oscillating?