CircuitMaker Model for 12AY7/6072

[rlaury]

Hi Group:
Does anybody have a CM model for a 12AY7/6072.
I know its possibe to take a 12AT7 and modify it
but I'm not sure if all you change Rp and the C's
or is there more.
Anybody had any sucess doing this?


Vacuum Tube Triode pkg:VT-9 (A:1,2,3)(B:6,7,8)
.SUBCKT X12AT7 P G K
BP P K I=6.717E-6*URAMP(V(P,K)+63.19*V(G,K))^1.5
CGK G K 2.2P
CGP G P 1.5P
CPK P K 0.5P
.ENDS X12AT7

RonL

 

[PRR]

> I'm not sure if all you change Rp and the C's or is there more.

Rp does not appear in the model. The Cs will be very similar from AT to AY (within 1pF), and not involved in mid-band gain, so I would not tamper them for a first-crack model.

BP P K I=6.717E-6*URAMP(V(P,K)+63.19*V(G,K))^1.5

This is the basic equation: the PK and Mu*GK voltages, times a constant current, all raised to 3/2 power. There are good theoretical reasons for this form and the 3/2 power; no real tube obeys theory very exactly; but at "normal" operating points this gives fairly-good results.

Replace 63.19 (idealized Mu of the 12AT7) with the book-value Mu of the 12AY7 (40). Set up a model of the spec-book "typical" operating condition(s). See what current this model says. Because the AY and AT are very similar, it should be nearly-right. Make small changes to the 6.717E-6 constant (basically the size and shape of the cathode) until your model current matches the spec-book (within 10%). If the book has two typical conditions, try both and find a compromise values of the 6.7.. constant that gives good results in both conditions. I would expect the "6.7..." to end up around 8 or 10, for the larger perveyance of the 12AY7.

 

[NewYorkDave]

FWIW, here's another 12AT7 model to play with:

* GENERIC: 12AT7 / ECC81
.SUBCKT X12AT7 A G K
* ANODE MODEL
BLIM LI 0 V=(URAMP(V(A)-V(K))^ 1 )* 0.0037
BGG GG 0 V=V(G)-V(K)--0.5
BRP1 RP1 0 V=URAMP(-V(GG)* 0.09869 )
BRP2 RP2 0 V=V(RP1)-URAMP(V(RP1)-0.999)
BRPF RP 0 V=(1-V(RP2)^ 1 )+URAMP(V(GG))* 0.1
BGR GR 0 V=URAMP(V(GG))-URAMP(-(V(GG)*(1+V(GG)* 0.012937 )))
BEM EM 0 V=URAMP(V(A)-V(K)+V(GR)* 45.093 )
BEP EP 0 V=(V(EM)^ 1.4 )*V(RP)* 0.00000863
BEL1 EL1 0 V=URAMP(V(EP))
BEL EL 0 V=V(EL1)-URAMP(V(EL1)-V(LI))
BLD LD 0 V=URAMP(V(EP)-V(LI))
BAK A K I=V(EL)
* GRID MODEL
BGF GF 0 V=(URAMP(V(G)-V(K)--0.5 )^1.5)* 0.00012
BG G K I=V(GF)+V(LD)
* CAPS
CAK A K 0.0000000000004
CGK G K 0.0000000000023
CGA G A 0.0000000000016
.ENDS X12AT7

 

[rlaury]

Thanks Guy's
I'm trying to optimize the first stage of a new
preamp using a 6072A. It's transformer input (1:7)
and the output of the first stage see's one end of a 100K
stepped attenuator. I've ended up with a Vbb=225 and Ra=47K
Rk= 1.2K (non bypassed).

The design goal here is:
Min THD and IM distortion.
Set gain to handle appropriate levels from the input transformer.
(-60 to -20 Dbv)
Be able to drive the 100K stepped attenuator.

I've got the 12AT7 model pretty close for now thanks to you guys.


RonL