Re: Building a 3-1000z VTTC

>3.  The tube specs state the the filament needs 7.5V at 21.3A.  The
>filament transformer that came in the box is a 7.5V, 25A.  Is this OK or
>do I need to drop the current somehow (add series resistance?)

The 25A is the max the transformer is rated to put out. What the tube
actually draws is dependent on the filament itself. The resistance of the
filament will change pretty dramatically with temperature, which is in turn
influenced by the power dissipation of the tube (as well as the voltage).
Generally, you want to set the voltage on the filament, and monitor the
current to see if it is grossly high or low.  Its about 160 Watts, so a
small variac might be a good way to adjust the filament voltage.  Bring it
up slow the first time.

Read the manual for the tube! 3-1000Z has a thoriated filament which makes
it more efficient, but also much pickier about proper operation (unless you
don't care about the life of your $1000 tube)

I note that the Richardson catalog (http://www.rell-dot-com) says 8V at 20A for
the filament and 6kV for the anode (3kW RF out)