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On PSUD2 you would enter the off-load RMS voltage of one leg, so for 800V CT that would be 400 (probably a bit more than that as PSUD expects the off-load voltage). It multiplies by 1.414 automatically for you to get the peak. You're right, SPICE based programs don't do this and you have to take the additional step of multiplying by SQRT(2).

You'd probably want the edit transformer properties to look something like this:



Note the [...] buttons at the right of the two fields above.

The first button at the end of the Value field brings up the off-load voltage calculator. This takes a guess at the off-load voltage given the transformer nominal RMS voltage, rated current, and regulation in %. Small transformers would be about 10%, bigger ones around 5% but the manufacturers data sheets should give some help with this. You could get something like the following for your 800V CT transformer:



The second button after the Source res field uses resistance measurements and real-world voltage measurements to dial in the transformer values. For secondary resistance, just measure one leg of the secondary - CT to outer. For example, if you measure a primary of 5 ohms and a secondary of 68 ohms on one leg, followed by voltage measurements of 121V AC on the primary and 418V RMS on one leg of the secondary you could end up with the following:



In this case, you would use a transformer voltage of 418V in PSUD with a source impedance of 127.7 ohms. It's an estimate, and gets messed up if you have windings for filaments etc., but it should put you in the right ball park.

Hope this helps.

Regards,
Duncan

On 7/29/2022 12:26 PM, Rulg wrote:

Spice LT ... i have to enter V * 1.414

Duncan PSUD and power transformer makers "assume" AC power is sinusoidal. (For several reasons, it always is, nearly.) And because the original load on AC power systems was light-bulbs and heaters (and motors, a special case), which hot-up and put-out according to the RMS of the wave, RMS is the conventional spec.

SPICE is an all-purpose equation solver and does not make this assumption for you. A full SPICE pack has square, triangle, and other waves as user-defined. The convention is to specify the "peak" because that's always clearly defined no matter how wonky the wave shape is.

the Duncan spice model literature for the 6SL7 and 6SN7 also give a maximum plate beyond the spec sheet figures.

Yes, the "6SN7GTB, ECC32, 6FQ7/6CG7, 5692" model:

--says 0..450V. I think some of these tubes are rated for 450V steady. And the 330V DC tubes will swing their plates above 330V in transformer-loaded circuits, with complete safety (because they spend the other half of the time below 330V). We need to model transient conditions. No, a tube does not blow-up the instant it sees more than the steady rating.

i can't afford to blow stuff up

I believe smoke is the best teacher. However too much smoke is bad; and tubes don't smoke when they die. But tubes do not die easy. Running tube plates 40% over rating is not uncommon. They make more trouble that way, and in 1950 RCA/GE would prefer to sell you a higher-priced tube with bigger numbers, but if you watch your voltmeter at power-up you can easily shut-down long before you kill a tube.

Electrolytic capacitors at over-voltage can die in a minute or so, AND they spit damp paper at the ceiling (or your face).