EF86 spice model is tetrode or pentode?

[Joseph R]

Hi,

I'm trying to simulate a mic preamp with an EF86. The problem is that all spice model avaible on the net have only 4 connections like in this one
*Vacuum Tube Tetrode EF86
.SUBCKT XEF86 A S G K

*
* Calculate reduction in mu when Vg < -3V
*
Bmu mu 0 V=V(G,K)+URAMP(V(K,G)-3)*0.4
*
* Calculate contribution to cathode current
*
Bat at 0 V=0.636*ATAN(V(A,K)/15)
Bgs gs 0 V=URAMP(V(S,K)/27.5+V(mu)*1.32+1)
Bgs2 gs2 0 V=URAMP(V(gs))^1.5
Bcath cc 0 V=V(gs2)*V(at)
*
* Calculate anode current
*
Ba A K I=5.83E-4*V(cc)
*
* Calculate screen current
*
** S K I=0.5E-3*V(gs2)*(1.1-V(at))
*
* Capacitances
*
Cg1 G K 3.8p
Cak A K 5.3p
Cg1a G A 0.05p

.ENDS XEF86

But the EF86 is a pentode!!

Can somebody please explain me why all model are tetrode and if there is somewhere a pentode model for this tube?

 

[unclejed613]

because 99.99% of the time, the suppressor is connected directly to the cathode, and the tube is modeled as a tetrode with pentode characteristics. the only exception would be if you were using the suppressor as a gain control element, and that isn't done very often. a pentagrid converter was usually used for that. more often, the screen grid is used as the multiplier input on a pentode.

 

[Joseph R]

thanks for reply.
I wanted to build a mic preamp and the suppressor grid is connected to ground and I want to know how much gain it produce.

 

[unclejed613]

is the cathode also grounded?

 

[Joseph R]

no trough resistor and bypass cap