[AMPS] 3-500Z Grid Current Rating

[David A. Pruett]

Mike,

It sounds to me like your loading is too light, resulting in excessive grid
current for the amount of output power.  I've seen this often happen on
amplifiers where the plate tuning C is critical (as it often is on a 50 MHz
amp).  I've seen this on my Henry 2K-3 which uses a Pi-L and seems to have
several settings where a reasonable amount of output power can be obtained,
but when you start looking at the grid and plate currents, something seems
awry.  Someone once told me that with the Eimac triodes in G-G, a rough
rule of thumb is 1:3 ratio between grid and plate currents.

I've found with my Henry that using the old "dip and load" technique always
leads to the best operating condx.  Start with the loading cap fully
meshed.  As you adjust the plate cap you should see a VERY sharp dip in
plate current with a correspondingly sharp peak in grid current.  Increase
the loading (i.e. reducing the load C) slightly, dip again, and repeat
until max power out occurs.

If this seems pretty fundamental, please don't take offense.  However, this
method has solved several tuning problems here at K8CC.  With modern gear
there sometimes is a tendency to simply tune for max output without paying
close attention to the grid/plate.  Moving from one band to another
sometimes fosters this mistake (not an issue with a monoband 50 MHz
final!).

73,

Dave/K8CC


--
FAQ on WWW:               http://www.contesting.com/ampfaq.html
Submissions:              amps@contesting.com
Administrative requests:  amps-REQUEST@contesting.com
Problems:                 owner-amps@contesting.com
Search:                   http://www.contesting.com/km9p/search.htm