[AMPS] one more mla2500 question

[Joe Subich, W8IK]

At 08:23 AM 2/16/98 -0800, you wrote:
>
>Mr. Subich:  On the 8873/4/5 and 3cx800A7 Eimac spec. sheet, no maximum grid 
>current rating appears to be given.  
>
>

I have in my possession EIMAC data sheet  357655/VA4588 (Effective 1 Dec 1983) 
for the 3CX800A7 that gives the following data for "typical operation" in 
cathode driven class AB2 service (to 150 MHz):

    Plate voltage ...........  2200  V
    Cathode Bias voltage ....  +8.2  V
    zero signal plate current  .015  A
    CW plate current ........  .500  A
    CW power input ..........  1100  W
    PEP input power .........  1100  W
    two-tone plate current ..  .313  A (1)
    CW grid current .........  .036  A (2)
    two-tone grid current ...  .016  A (1)
    peak RF cathode voltage .    16  W (2)
    peak driving power ......    23  W (2)
    useful output power .....   750  W
    useful output power, PEP .  750  W
    cathode input impedence ..   54  Ohm
    resonant load impedence .. 2700  Ohm
    IMD, 3rd order ...........  -36  dB (3)
         5th order ...........  -32  dB

  notes:  
      (1) value will be lower with voice modulation 
          for the same PEP level
      (2) approximate value
      (3) reference one tone of a 2-equal-tone signal


This is for a tube with a grid with an "ABSOLUTE MAXIMUM DISSIPATION"
of 4 WATTS.  If *YOU* want to be stupid and push the grids harder than 
that, be my guest.  However, I would treat 36 mA per tube grid current 
as an effective maximim and look for no more than 30 mA of total (two 
tubes) grid current with voice modulation (for the MLA-2500, Alpha 76, 
or any other amplifier with 8874/8875/3CX800A7 type tubes).  The extra 
dB of splatter isn't worth $500+ in replacement tube costs. 



73, 

   ... Joe Subich, W8IK  ex-AD8I
       <w8ik@ibm.net>

"Hindsight is an exact science."


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