As you've deduced, they are the cheapest brand going. That means they are the most economical, and that's good. Are they the 'best' brand going? I really doubt it, the best is never the cheapest.
And just for for grins. That first number in a tube designator such as the '3-500' series, tells you the number of elements in that tube. That means that a '2-500zg' is one hell of'va big diode, or rectifier. A pair of them would make a very high current full wave rectifier and power supply. Bet the required transformer for that thing would weigh a ton.
- 'Doc
(I know it was a 'typo'.) |