[Amps] AL-1200 Grid Current - negative?
r at somis.org
Sun Nov 9 07:56:01 EST 2003
*** To find out, remove the tube and fire it up. If the grid current is
zero, the chances of the 3cx1200A7 having a filament to grid short are
pretty good. However, this is a rare occurence compared to 3-500Zs.
Rather than replacing a 3cx1200A7, I would look at modifying the amp to
take a 3cx1200Z7, a tube which has 0.075pF of feedback C - as opposed to
0.2pF of feedback C for the 3cx1200A7. The price of a Z7 is c. $20 more
than an A7.
>What does it mean when you power up an AL-1200 and the grid current meter
>pins negative (no drive power supplied)?
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