No problem Keenan
There are quite a few things that you can pull from LTSpice. When designing a circuit, I like to work from the load backwards; Determine the headphones/speakers/etc. that will be hooked up to the amp. You can then choose the output transformer based on the needed power into that load. Higher primary impedance usually gives lower distortion, but less power. Headphones are an easy load, so best to choose a high(er) primary impedance. Your chosen output transformer (LL2765) is a good choice for this. Then you can determine how much swing into the primary of the transformer is necessary to get the desired output power you want into the pair of headphones/speakers, and design the rest of the circuit from there (e.g. making sure that your driver tube can swing enough voltage at low enough distortion, and ditto for the power tube).
Some of the biggest things that I find LTSpice helps me check is to make sure that the power supply is built robustly. It's always good to do simulations at multiple frequencies (e.g. sim 20Hz, 40Hz, 100Hz, 1000Hz, etc.) to make sure you have low enough power supply ripple at all frequencies. You can also run a frequency sweep and check for any roll-off or abnormalities on the output (e.g. low end roll-off if the coupling cap or cathode bypass caps aren't sized right, or high-freq roll-off if the grid resistors are too high value, etc. etc.). Good to make sure that the circuit behaves how you want it to both when your wall voltage is low (as low as 110V) and that nothing will fry/blow out if wall voltage goes high for some reason (e.g. 140V). LTSpice is also good at calculating the effects of negative feedback if the tube models are good (though I don't use negative feedback myself in my designs). Also good for checking to make sure that supply voltages are always above the drop-out voltage of any linear regulators you use. Also good to check that the B+ voltage always stays above the drop-out voltage for the constant current source that you are using or there will be some major distortion from the driver stage. LTSpice is a more accurate simulation than PSUD2 for the power supply. Also good to send some transients through the circuit to look at various nodes for oscillations. This is especially important when choosing capacitor sizes and choke inductance(s) in the power supply. There are probably lots of things that I'm not remembering right now... too full of junk food from the Christmas buffet at my lab.
Here are some factors that I've come across when choosing tube vs. ss rectification:
Tube rectifier pros:
- They look so cool!
- Tube rolling allows you to play around with circuit operating points
- They give the amp more of a "vintage tone" that can be very pleasant to the ear, and the tone can be varied to some degree by choice of rectification tube. (But see next section on cons)
- Less tendency to cause transformer ringing and less diode switching noise than ss rectification
Tube rectifier cons:
- The tone qualities from tube rectifiers is due in part to what is known as voltage "sag" when the tube rectifier is asked to provide greater current, and then the tube rectifier shows voltage "bloom" as it recovers and overshoots. This leads to less defined, slower and "woolly" bass, and less clarity/precision in high frequencies.
- Larger voltage drop across the tube
- Additional heater supply needed
Solid State diode pros:
- Less voltage drop
- No heater supply
- Does not show sag and bloom like tube rectifiers
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If done right: Can design for extremely low power supply noise & better bass and clarity in mids and high frequencies than can be achieved with tube rectification alone
Solid State diode cons:
- Doesn't look as good
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If done wrong: Can cause more transformer ringing, and current spiking/diode switching noise can reverberate throughout the power supply (and into the signal) resulting in a harsher sounding amp
How to do solid state rectification right: Employ RC transformer snubbers for transformer and supply zeta=1 ("critical") damping, use fast soft-recovery diodes (e.g. hexfreds, SiC Schottky's, etc.), bound rectifiers with resistance before and after the diode to decrease current spiking (which can cause supply ringing), and use capacitance multipliers and other Mosfet filtering techniques to bring power supply ripple down to extremely low levels. Also possible to build in soft-start without too much difficulty. An example: Leftside's amp has no electrolytic caps in the high voltage supply (lots of big 85uF oil caps with no electrolytic distortion), and B+ power supply ripple is under 30uV
The higher distortion at higher voltage operating points can be compensated to some degree by using output transformers with higher primary impedance (however, higher primary impedance means lower max output power, so always tradeoffs).
