First Watt SIT5

[generg]

Inspired by lhquam success.....
I tried his way to make the biasing of the output stage, hope I got his decisive idea right.

Because I have no real understanding, it was all done by try and error or copy and paste....
:--))

Helas, I am no lhquam, no ZM and no Nelson of course, so there might be severe faults. You all know LTspice is patient, reality often not.

Please comment. How much current do I need to get the 35Watt with 60V rails?

 

[Nelson Pass]

Something around 1.5 to 1.6 amps

😎

 

[generg]

Thank you Nelson!

:--))

 

[generg]

A bit higher current and I adjusted the source resistors at the output to get more contribution of the SIT (green), blue MosFet.

Of course do not take my draft too seriously it is more "entertainment than analysis" to vary a well-known saying....

:--))

 

[generg]

LTSpice says the currents of SIT and MosFet are fairly stable over temperature.....
Did Nelson say because of the high source resistor? I think he did....

 

[lhquam]

The Rothacher SIT model does not include tempco, so LTSpice cannot tell you much.
However, the resistor from source-to-source doesn't have to be very big for the bias current to be stable.

 

[generg]

AAHHH! Thank you Lynn! How do I see if a model includes the tempco?

 

[lhquam]

Look at the Rothacher 2SK182ES Spice .SUBCKT model. There are temperature related parameters or computations in that model.

 

[generg]

I am afraid I occupy you....

Where is the tempco hidden in the SK180 file?

*2SK180
*GENERATED BY SIT MODELER @ AUDIOHOBBY.COM
*MODEL RANGE: 100V, 2A
*--------------------------------------------------
.SUBCKT 2SK180 D G S ; Drain Gate Source
+ PARAMS: MU=16 X=1.8 K=0.225 N=1.72 VCT=0 RG=2MEG
*--------------------------------------------------
B1 D S I=K*PWR(URAMP((V(G,S)+VCT)+(N*LN(V(D,S))+(V(D,S)/MU))),X)
FOR MULTISIM COMMENT OUT ABOVE LINE () AND UNCOMMENT NEXT LINE
*B1 D S I=K*PWR(MAX((V(G,S)+VCT)+(N*LN(V(D,S))+(V(D,S)/MU)),0),X)
R1 G S {RG}
CGS G S 1500P
CGD G D 0P
CDS G S 0P
.ENDS 2SK180
*--------------------------------------------------


.SUBCKT THF51S 1 2 3 ; Drain Gate Source
+ PARAMS: MU=19.4880 EX=1.204 KG1=0.7031 KP=81.0 KVB=42.0 VCT=2.0 RGI=1MEG
*--------------------------------------------------
E1 7 0 VALUE={V(1,3)/KP*LN(1+EXP(KP*(1/MU+(VCT+V(2,3))/SQRT(KVB+V(1,3)*V(1,3)))))}
RE1 7 0 1G
G1 1 3 VALUE={(PWR(V(7),EX)+PWRS(V(7),EX))/KG1}
RDS 1 3 1G ; TO AVOID FLOATING NODES
D1 5 2 DX ; FOR GRID CURRENT
R1 5 3 {RGI} ; POSITIVE GRID CURRENT
.MODEL DX D(IS=1N RS=1 CJO=10PF TT=1N)
.ENDS

 

[lhquam]

It is not hidden. There is no tempco in the SK180 file.

 

[generg]

May be you can post your .txt

 

[Ben Mah]

Here is what I have for the 2SK182ES:

 

[generg]

Thank you Ben!

I show them both here: And Lynn is there the tempco visible?

First one:

*--------------------------------------------------
*2SK182ES2
*GENERATED BY SIT MODELER @ AUDIOHOBBY.COM
*MODEL RANGE: 80V, 2A
*--------------------------------------------------
.SUBCKT 2SK182ES D G S ; Drain Gate Source
+ PARAMS: MU=16.98 X=2.56 K=0.443 N=1.6 VCT=0 RG=2MEG
*--------------------------------------------------
B1 D S I=K*PWR(URAMP((V(G,S)+VCT)+(N*LN(V(D,S))+(V(D,S)/MU))),X)
FOR MULTISIM COMMENT OUT ABOVE LINE () AND UNCOMMENT NEXT LINE
*B1 D S I=K*PWR(MAX((V(G,S)+VCT)+(N*LN(V(D,S))+(V(D,S)/MU)),0),X)
R1 G S {RG}
CGS G S 2600P
CGD G D 0P
CDS G S 0P
.ENDS 2SK182ES
*--------------------------------------------------


Second one:

*--------------------------------------------------
*2SK182ES2
*GENERATED BY LHQUAM
*
*--------------------------------------------------
.SUBCKT 2SK182ES2 D G S ; Drain Gate Source
+ PARAMS: MU=16.98 X=2.56 K=0.443 N=1.6 VCT=0 RG=2MEG
*--------------------------------------------------
B1 D S I=K*PWR(URAMP((V(G,S)+VCT)+(N*LN(V(D,S))+(V(D,S)/MU))),X)
FOR MULTISIM COMMENT OUT ABOVE LINE () AND UNCOMMENT NEXT LINE
*B1 D S I=K*PWR(MAX((V(G,S)+VCT)+(N*LN(V(D,S))+(V(D,S)/MU)),0),X)
R1 G S {RG}
CGS G S 17.7nF ; Ciss-Crss
CGD G D 0P ; Crss need a value here
CDS G S 0P ; Coss-Crss
.ENDS 2SK182ES2
*--------------------------------------------------

 

[Ben Mah]

I found the following on this post: https://www.diyaudio.com/community/threads/the-simplest-defisit-with-2sk182es.373528/post-6693502

 

[generg]

Thank you, Ben!

May be Lynn will come in and show us the tempco coefficients.

 

[Ben Mah]

VCT?

 

[lhquam]

As I said several times, the Rothacher SIT model does not include modeling of temperature. It is a functional model described by the equation I=K*PWR(MAX((V(G,S)+VCT)+(N*LN(V(D,S))+(V(D,S)/MU)),0),X), with inter-electrode capacitances added.

Unfortunately, Micheal Rothacher's paper: "A Concise Model for Static Induction Transistor IV Characteristics" is only available by purchasing Linear Audio Vol 6.

 

[generg]

You were right Ben!

:--))

 

[generg]

I have this article....

it is on Micheal homepage free available.....

:--))

https://passdiy.tv/mrarticles/sitmodel.pdf

 

[lhquam]

In Koren's paper "Finding SPICE tube model parameters" https://www.normankoren.com/Audio/Tube_params.html, there is a description of the VCT parameter:

VCT [0] Contact potential. An offset voltage on the grid that makes curves appear as if they are going positive on a few older tube types (RCA, Sylvania 12AX7, 12AU7).​