Did a little more digging. The "354A" is close to the right shape. Hard to tell scale from just this pic http://www.tubeworld.com/354a.jpg though... Not real obvious that there is actual mercury rolling around inside these either. Now I haveta research "mercury-vapor thyratron". Like I have time for this.. Oh well. Beats "work", I guess.Ted - that big tube image I just posted was a huge mercury-arc rectifier. Google "mercury-arc rectifier" and see if your tube shows up in image search.