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Problem with KT88 Williamson LTSpice simulation

Hi,

Can someone please tell me why I'm getting 100+KV on the grids of the KT88s in this simulation? The valves are dissipating 100+KW!

Thanks.

LTSpice schematic.jpg

\\\M:\Entertainment\HiFi\Valve stuff\Williamson Amplifier Material\LTspice model\LTSpice Schematic.jpg
 

Attachments

  • kt88 williamson.zip
    4.8 KB · Views: 36
So now I have the dc operating points. When I try to run 10ms of 4Khz sine wave I get:

WARNING: Node U3:A is floating.
WARNING: Node U3:K is floating.
WARNING: Node U3:G2 is floating.
WARNING: Node U3:G1 is floating.
WARNING: Node U4:A is floating.
WARNING: Node U4:K is floating.
WARNING: Node U4:G2 is floating.
WARNING: Node U4:G1 is floating.

WARNING: Less than two connections to node N008. This node is used by R16.
WARNING: Less than two connections to node N030. This node is used by R19.
WARNING: Less than two connections to node N031. This node is used by L4.
WARNING: Less than two connections to node N012. This node is used by L5.
WARNING: Less than two connections to node N011. This node is used by R20.
WARNING: Less than two connections to node N027. This node is used by R21.
WARNING: Less than two connections to node N033. This node is used by R22.
WARNING: Less than two connections to node N004. This node is used by L1.
Direct Newton iteration for .op point succeeded.
Ignoring empty pin current: Ix(u3:anode)
Ignoring empty pin current: Ix(u3:screen)
Ignoring empty pin current: Ix(u3:grid)
Ignoring empty pin current: Ix(u3:cathode)
Ignoring empty pin current: Ix(u4:anode)
Ignoring empty pin current: Ix(u4:screen)
Ignoring empty pin current: Ix(u4:grid)
Ignoring empty pin current: Ix(u4:cathode)
Ignoring empty pin current: Ix(u3:anode)
Ignoring empty pin current: Ix(u3:screen)
Ignoring empty pin current: Ix(u3:grid)
Ignoring empty pin current: Ix(u3:cathode)
Ignoring empty pin current: Ix(u4:anode)
Ignoring empty pin current: Ix(u4:screen)
Ignoring empty pin current: Ix(u4:grid)
Ignoring empty pin current: Ix(u4:cathode)
Singular matrix: Check node u3:g1
Iteration No. 2
Fatal Error: Singular matrix: check node u3:g1
Iteration No. 2

This circuit has floating nodes.


Is there still a problem with the KT88 model?
 

Koonw

Member
2013-04-09 9:37 pm
So now I have the dc operating points. When I try to run 10ms of 4Khz sine wave I get:

WARNING: Node U3:A is floating.
WARNING: Node U3:K is floating.
WARNING: Node U3:G2 is floating.
WARNING: Node U3:G1 is floating.
WARNING: Node U4:A is floating.
WARNING: Node U4:K is floating.
WARNING: Node U4:G2 is floating.
WARNING: Node U4:G1 is floating.

WARNING: Less than two connections to node N008. This node is used by R16.
WARNING: Less than two connections to node N030. This node is used by R19.
WARNING: Less than two connections to node N031. This node is used by L4.
WARNING: Less than two connections to node N012. This node is used by L5.
WARNING: Less than two connections to node N011. This node is used by R20.
WARNING: Less than two connections to node N027. This node is used by R21.
WARNING: Less than two connections to node N033. This node is used by R22.
WARNING: Less than two connections to node N004. This node is used by L1.
Direct Newton iteration for .op point succeeded.
Ignoring empty pin current: Ix(u3:anode)
Ignoring empty pin current: Ix(u3:screen)
Ignoring empty pin current: Ix(u3:grid)
Ignoring empty pin current: Ix(u3:cathode)
Ignoring empty pin current: Ix(u4:anode)
Ignoring empty pin current: Ix(u4:screen)
Ignoring empty pin current: Ix(u4:grid)
Ignoring empty pin current: Ix(u4:cathode)
Ignoring empty pin current: Ix(u3:anode)
Ignoring empty pin current: Ix(u3:screen)
Ignoring empty pin current: Ix(u3:grid)
Ignoring empty pin current: Ix(u3:cathode)
Ignoring empty pin current: Ix(u4:anode)
Ignoring empty pin current: Ix(u4:screen)
Ignoring empty pin current: Ix(u4:grid)
Ignoring empty pin current: Ix(u4:cathode)
Singular matrix: Check node u3:g1
Iteration No. 2
Fatal Error: Singular matrix: check node u3:g1
Iteration No. 2

This circuit has floating nodes.


Is there still a problem with the KT88 model?

I forget to tell you: replace all "^" with "**" in KT88.inc, if you use LTSpsice
 

Koonw

Member
2013-04-09 9:37 pm
I now have the KT88 grids at -60V with a 120V peak-to-peak 4khz signal (swinging between 0V and -120V).

But there's only noise on the output.

Updated files attached.

Any suggestions please?

View attachment 536939

I don't all the asy so I use mine, it works.
 

Attachments

  • 6GU7 Williamson with KT88 dc op.asc
    10 KB · Views: 42
  • snapshot-1.png
    snapshot-1.png
    255.4 KB · Views: 70
Last edited:
Thanks koonw. I'm not getting the same result as you though.

I downloaded your file and adjusted the potentiometer and kt88 includes.

When I run the sim I get a 4khz output with an amplitude of only 50uV centred on 55uV instead of the 30V centered on 0V that you have.

The only difference I can suggest is the kt88 model. The one I'm using is attached.
 

Koonw

Member
2013-04-09 9:37 pm
Thanks koonw. I'm not getting the same result as you though.

I downloaded your file and adjusted the potentiometer and kt88 includes.

When I run the sim I get a 4khz output with an amplitude of only 50uV centred on 55uV instead of the 30V centered on 0V that you have.

The only difference I can suggest is the kt88 model. The one I'm using is attached.

Use a notepad, replace all "^" with "**" as follow, NO need to change pin tetrode asy (unless you have changed it, check) as mentioned earlier, the problem is in the model file as it is not a native LTSpice file, so apply to other model as well.

*
* Generic pentode model: KT88
* Copyright 2003--2008 by Ayumi Nakabayashi, All rights reserved.
* Version 3.10, Generated on Sat Mar 8 22:42:55 2008
* Plate
* | Screen Grid
* | | Control Grid
* | | | Cathode
* | | | |
.SUBCKT KT88 A G2 G1 K
BGG GG 0 V=V(G1,K)+0.99999999
BM1 M1 0 V=(0.097534908*(URAMP(V(G2,K))+1e-10))**-1.4398564
BM2 M2 0 V=(0.51022901*(URAMP(V(GG)+URAMP(V(G2,K))/5.0214944)))**2.9398564
BP P 0 V=0.0031096914*(URAMP(V(GG)+URAMP(V(G2,K))/9.8416483))**1.5
BIK IK 0 V=U(V(GG))*V(P)+(1-U(V(GG)))*0.0029317575*V(M1)*V(M2)
BIG IG 0 V=0.0015548457*URAMP(V(G1,K))**1.5*(URAMP(V(G1,K))/(URAMP(V(A,K))+URAMP(V(G1,K)))*1.2+0.4)
BIK2 IK2 0 V=V(IK,IG)*(1-0.4*(EXP(-URAMP(V(A,K))/URAMP(V(G2,K))*15)-EXP(-15)))
BIG2T IG2T 0 V=V(IK2)*(0.88165022*(1-URAMP(V(A,K))/(URAMP(V(A,K))+10))**1.5+0.11834978)
BIK3 IK3 0 V=V(IK2)*(URAMP(V(A,K))+1850)/(URAMP(V(G2,K))+1850)
BIK4 IK4 0 V=V(IK3)-URAMP(V(IK3)-(0.0020406477*(URAMP(V(A,K))+URAMP(URAMP(V(G2,K))-URAMP(V(A,K))))**1.5))
BIP IP 0 V=URAMP(V(IK4,IG2T)-URAMP(V(IK4,IG2T)-(0.0020406477*URAMP(V(A,K))**1.5)))
BIAK A K I=V(IP)+1e-10*V(A,K)
BIG2 G2 K I=URAMP(V(IK4,IP))
BIGK G1 K I=V(IG)
* CAPS
CGA G1 A 1.2p
CGK G1 K 9p
C12 G1 G2 6p
CAK A K 10.9p
.ENDS