LTSpice model for output transformer

[Sisqo9]

Hi jazbo8. I am trying to simulate my 18W Marshall clone amplifier on LTSpice, but I am a complete noob when it comes this. How do I use this transformer model? I get how one adds the model file to the same directory as your LTSpice file and then one can add the model under the "spice directive" button in LTSpice and you lay the text somewhere by the circuit. I am assuming I create a transformer by using inductors, but then how do I relate the model you gave to the those inductors? Your help would be greatly appreciated. I am using two EL84 power tubes in push-pull configuration and I will have an 8 ohm load. Thank you

[Sisqo9]

Hi jazbo8. I am trying to simulate my 18W Marshall clone amplifier on LTSpice, but I am a complete noob when it comes this. How do I use this transformer model? I get how one adds the model file to the same directory as your LTSpice file and then one can add the model under the "spice directive" button in LTSpice and you lay the text somewhere by the circuit. I am assuming I create a transformer by using inductors, but then how do I relate the model you gave to the those inductors? Your help would be greatly appreciated. I am using two EL84 power tubes in push-pull configuration and I will have an 8 ohm load. Thank you

[Dave H]

Try this one. It's nearly an 18W Lite. Extract the .inc and .asc files to the same directory.

18 watt.zip

[trobbins]

Just love a model that uses this example of precision:

LP1 1 B 2.71099224897965

[nickb]

Just love a model that uses this example of precision:

LP1 1 B 2.71099224897965

Probably derived by back calculation from the frequency response.

In the Heyboyer model (towards the top) the the secondary DC resistances for the three taps are specified at 8, 4 and 3 ohms. That is not right. I suspect it should be 0.8, 0.4 and 0.3.

Corrected model:

.SUBCKT 18W_OPT P1 B P2 O16 O8 O4 Com
* Push Pull Transformer
* 10800 to 16 Ohms, -3db 80 to 15000 Hz
* Taps at 4 and 8 Ohms
* Heyboer_HT-6135
*   
LP1 1 B 2.71099224897965
LP2 2 P2 2.71099224897965
LA1 5 O8 0.00263122532543707
LA2 6 O4 0.00131561266271854
LA3 7 Com 0.00766795252904828
KALL LP1 LP2 LA1 LA2 LA3 0.975660566768592
RP1 P1 1 80
RP2 B 2 80
RS1 O16 5 0.8
RS2 O8 6 0.4
RS3 O4 7 0.3
.ENDS 18W_OPT

[trobbins]

I'm so pleased they concatenated to 14 decimal place precision, and didn't try to use full PI precision, as that may need a bit more than 64-bit processing

Even common sims like PSUD2 need a quick double check, as they also use public contributed models, which can lead one astray after innocently choosing a dud model.

[trobbins]

I have a Hyeboer 18W HT-6135 output transformer. I know the turns ratios an nominal impedance in ohms but SPICE wants the impedance in Henrys.

I have tried measuring the impedances but although I have a decent oscilloscope I don't have an even half way decent signal generator so I didn't get very far with that.

The common vintage method to test primary primary winding inductance of an OT is to connect the winding across a 5VAC or 6.3VAC transformer winding, and insert a mA meter in series with the winding. Or insert a 10ohm or 100ohm or 1k resistor in series and measure the voltage across the current sensing resistor. And then measure the voltage across the winding, and calculate the winding impedance, and hence inductance at the mains frequency.