[Amps] Question about grid current in 4CX or 3CX

[sm0aom at telia.com]

Usually the  Class C grid current decreases somewhat when the plate and screen voltages are applied,
due to more electrons are drawn away from the grid.

The actual grid dissipation can be estimated as a first approximation by 
applying Chaffee analysis to the constant-current curves
in the data sheets, such as done in the Eimac AB-5.

For the 4CX10000D at full ratings in class C, using data sheet values, 
the grid dissipation becomes the difference between the power consumed by the bias source 
which is the product of the DC grid current and the DC bias voltage;

350*0,25 = 87,5 W

and the driving power

590*0,25 = 147 W

= 147-87,5 = 59 W

which is less than 75 W  which is the allowed grid dissipation.

If the plate and screen voltages are removed, the dissipation would increase somewhat,
so full drive may not be advisable for longer periods.

73/

Karl-Arne
SM0AOM

----Ursprungligt meddelande----
Från : dj7ww at t-online.de
Datum : 2019-03-18 - 09:19 (CEST)
Till : donroden at hiwaay.net, amps at contesting.com
Ämne : Re: [Amps] Question about grid current in 4CX or 3CX

Hi Don,

The grid dissipation of the 4CX10000D is 75W.
It takes 150W of drive for 250mA of grid current with that tube in class-c
with anode and screen voltage supplied.

Are you thinking of a different tube?

73
Peter


-----Original Message-----
From: Amps [mailto:amps-bounces at contesting.com] On Behalf Of
donroden at hiwaay.net
Sent: Freitag, 15. März 2019 16:38
To: amps at contesting.com
Subject: [Amps] Question about grid current in 4CX or 3CX


Question :


For the larger tubes with handles  ( commercial service )

Does grid current increase or decrease as plate voltage and screen  
voltage is removed. ?

If it takes 250 watts to produce 100ma of grid current in a 4CX10,000.
is the grid just a big dummy load and is it doing the tube harm to  
dump 250 watts into it when both plate and screen voltages are removed ?


Don W4DNR


_______________________________________________
Amps mailing list
Amps at contesting.com
http://lists.contesting.com/mailman/listinfo/amps

_______________________________________________
Amps mailing list
Amps at contesting.com
http://lists.contesting.com/mailman/listinfo/amps