EF86 spice model is tetrode or pentode?

Joseph R · 12th February 2010, 04:13 PM

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 · 06:26 PM

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 · 20th February 2010, 07:39 PM

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 · 20th February 2010, 07:57 PM

is the cathode also grounded?

Joseph R · 20th February 2010, 08:00 PM

no trough resistor and bypass cap

12th February 2010, 04:13 PM	#1
Joseph R diyAudio Member Join Date: Oct 2008	EF86 spice model is tetrode or pentode? 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=0.636ATAN(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-4V(cc) * Calculate screen current * ** S K I=0.5E-3V(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?

20th February 2010, 06:16 PM	#2
unclejed613 diyAudio Member Join Date: Dec 2006	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. Last edited by unclejed613; 20th February 2010 at 06:26 PM.

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20th February 2010, 07:39 PM	#3
Joseph R diyAudio Member Join Date: Oct 2008	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.

20th February 2010, 07:57 PM	#4
unclejed613 diyAudio Member Join Date: Dec 2006	is the cathode also grounded?

20th February 2010, 08:00 PM	#5
Joseph R diyAudio Member Join Date: Oct 2008	no trough resistor and bypass cap