[Amps] 3-500Z Tubes

[R.Measures]

>The 3-500Z tubes in my AMP INT 3-500ZC amplifier are shorted between
>filament and grid.  There may be more wrong but this is a start.
>
>Question.  What is my best source for obtaining the 3-500Z tubes?  

•  Bee - - RF Parts is OK.

>Are  Eimac tubes still available?  

•  No. Triton bought out Eimac's glass tube division.

>Do I want the ZG with the graphite anode? 

•  Graphite anodes do not have the weak spotweld problem that late 
production Eimac and early production Triton tubes with metal 
anode-radiators have been plagued with.  Maybe Triton solved the problem 
by increasing spotweld-I?

>Will the G require any changes in the amp? 

•  No but the ZSAC should be adjusted to 75 to 85 mA per tube fot SSB.

> Do I need a matched pair? 

•  Probably not.

>What about non-USA made tubes?
>
•  Are graphite-anode 3-500Zs manufactured in the U.S.?