801a DHT Triode Spice Model

My friend Bela, who is an experienced DHT user and very fond of the 801a, asked me if I could help in developing an LTSpice model for the venerable 801a. I have several 10/10Y but unfortunately no 801a at hand to trace so I used the data sheet curves which are a bit challenging due to resolution/scaling of the characteristic curves:

I had to compromise the model fit as if you want accuracy in A1 region the matching is less than perfect in A2. Still, the model is not perfect but is very good for simulation purposes.

The interesting thing was to add the grid current model for A2 operation:

Well, looking to test this model, I chose the following operating point:

The data sheet grid space is a bit challenging, but looking at the model in LTSpice:

The following slight difference can be observed:

There’s about a 10% difference. Not bad considering the normal variance you’d expect in the valve anyway.

Here is the 801a-A2-model. Let me know your feedback:

**** 801A CURVES ** Composite DHT with Advanced Grid Current **************
* Created on 01/18/2016 19:48 using paint_kit.jar 2.9
* www.dmitrynizh.com/tubeparams_image.htm
* Plate Curves image file: 801a curves.png
* Data source link: RCA data sheet
*
* Model developed by Ale Moglia (c) 2016
* [email protected]
*
* www.bartola.co.uk/valves
*
*———————————————————————————-
.SUBCKT DHT-801A-A2 1 2 3 4 ; P G K1 K2
+ PARAMS: CCG=4.5P CGP=6P CCP=1.5P RFIL=6
+ MU=8 KG1=2984.1 KP=124.5 KVB=2083.2 VCT=-7.04 EX=1.29
+ VGOFF=1.17 IGA=0.00099 IGB=0.03 IGC=-18.3 IGEX=1.9
* Vp_MAX=800 Ip_MAX=250 Vg_step=10 Vg_start=100 Vg_count=20
* Rp=4000 Vg_ac=55 P_max=20 Vg_qui=-48 Vp_qui=300
* X_MIN=39 Y_MIN=33 X_SIZE=786 Y_SIZE=492 FSZ_X=1418 FSZ_Y=656 XYGrid=false
* showLoadLine=n showIp=y isDHT=y isPP=n isAsymPP=n showDissipLimit=y
* showIg1=n gridLevel2=y isInputSnapped=n
* XYProjections=n harmonicPlot=n harmonics=y
*———————————————————————————-
RFIL_LEFT 3 31 {RFIL/4}
RFIL_RIGHT 4 41 {RFIL/4}
RFIL_MIDDLE1 31 34 {RFIL/4}
RFIL_MIDDLE2 34 41 {RFIL/4}
E11 32 0 VALUE={V(1,31)/KP*LOG(1+EXP(KP*(1/MU+V(2,31)/SQRT(KVB+V(1,31)*V(1,31)))))}
E12 42 0 VALUE={V(1,41)/KP*LOG(1+EXP(KP*(1/MU+V(2,41)/SQRT(KVB+V(1,41)*V(1,41)))))}
RE11 34 0 1G
G11 1 31 VALUE={(PWR(V(32),EX)+PWRS(V(32),EX))/(2*KG1)}
G12 1 41 VALUE={(PWR(V(42),EX)+PWRS(V(42),EX))/(2*KG1)}
RCP1 1 34 1G
C1 2 34 {CCG} ; CATHODE-GRID
C2 2 1 {CGP} ; GRID=PLATE
C3 1 34 {CCP} ; CATHODE-PLATE
RE2 2 0 1G
EGC1 81 0 VALUE={V(2,31)-VGOFF} ; POSITIVE GRID THRESHOLD
GG1 2 31 VALUE={0.5*(IGA+IGB/(IGC+V(1,31)))*(MU/KG1)*(PWR(V(81),IGEX)+PWRS(V(81),IGEX))}
EGC2 82 0 VALUE={V(2,41)-VGOFF} ; POSITIVE GRID THRESHOLD
GG2 2 41 VALUE={0.5*(IGA+IGB/(IGC+V(1,41)))*(MU/KG1)*(PWR(V(82),IGEX)+PWRS(V(82),IGEX))}
.ENDS
*$

Author: Ale Moglia

"A mistake is always forgivable, rarely excusable and always unacceptable. " (Robert Fripp) View all posts by Ale Moglia