Morning gents, first time posting in the valve section 
In a new DAC project I'd like to use a 12AY7 valve buffer as output stage loosely based on a preamp design I built many moons ago and regret selling, even more so since I did not make proper notes back then.
The main design fun is in the rest of the circuit; the valve is just for fun and to add an integrated preamp of a design that I really liked. For the valve side there are a few things I'd like to shamelessly add in a single thread for those kind enough to share their wisdom on a field I have very little experience with:
- I recall some saying that starving the triode heater voltage can yield improvements, plus improving lifespan. I just blindly did it but did not do A-B testing between the usual 6.3V or 5.8V or whatever I settled on. Any comments?
- For a 'soft-start' circuit to similarly add series resistance to reduce thermal shock on turn-on, what is there a specific recommended amount? Once again, I remember using 30s delay but not the amount of current limit imposed with whatever series resistance I used.
- Is there any merit in super-regulating the heaters or will a standard LM317 or so suffice? Likewise with caps, several schematics explicitly reference all kinds of boutique electrolytics (Elna & Black Gate etc) on the heaters.
- I used a EZ81 rectifier: do all models sound the same or is there merit in splashing out on on a nice NOS model?
- The huge power supply (EZ81-10uF-10H-22uF-22H-33uF-12AY7) worked a treat but caused slow DC offsets (apparently called "motorboating") that slowly made the woofers visibly move back and forth. This was fixed with adding a series zener-follower before the 22uF and the 22H and I left it there, but ideas on improving this would be great.
- Original design used two different transformers, one for the triode power and EZ81 heater and another for the triode heaters (purely because of material availability). Is there advantage to this or can all the secondaries be combined on a single transformer without any performance penalty?
In a new DAC project I'd like to use a 12AY7 valve buffer as output stage loosely based on a preamp design I built many moons ago and regret selling, even more so since I did not make proper notes back then.
The main design fun is in the rest of the circuit; the valve is just for fun and to add an integrated preamp of a design that I really liked. For the valve side there are a few things I'd like to shamelessly add in a single thread for those kind enough to share their wisdom on a field I have very little experience with:
- I recall some saying that starving the triode heater voltage can yield improvements, plus improving lifespan. I just blindly did it but did not do A-B testing between the usual 6.3V or 5.8V or whatever I settled on. Any comments?
- For a 'soft-start' circuit to similarly add series resistance to reduce thermal shock on turn-on, what is there a specific recommended amount? Once again, I remember using 30s delay but not the amount of current limit imposed with whatever series resistance I used.
- Is there any merit in super-regulating the heaters or will a standard LM317 or so suffice? Likewise with caps, several schematics explicitly reference all kinds of boutique electrolytics (Elna & Black Gate etc) on the heaters.
- I used a EZ81 rectifier: do all models sound the same or is there merit in splashing out on on a nice NOS model?
- The huge power supply (EZ81-10uF-10H-22uF-22H-33uF-12AY7) worked a treat but caused slow DC offsets (apparently called "motorboating") that slowly made the woofers visibly move back and forth. This was fixed with adding a series zener-follower before the 22uF and the 22H and I left it there, but ideas on improving this would be great.
- Original design used two different transformers, one for the triode power and EZ81 heater and another for the triode heaters (purely because of material availability). Is there advantage to this or can all the secondaries be combined on a single transformer without any performance penalty?
