Paul, the tubes listed are all simular with the addition of the 40kg6a. There should be new Russian, hungarian and chinese tubes available for $25 a pop.
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You can switch EL519 or EL509 with a mod to your gear, these tubes have a 6.3 heater voltage where as the PL509/ PL519 have a 40 volt heater. I have not done it but have heard of a few that have with very good results. And the Russians have plenty of these and alot cheaper.