On a sweaty day like today, I can feel 12V. (Yes, sweat-damp skin can come down to a few K ohms.)
It is one of several numbers Generally Recognized As Safe.
42Vdc is related to 30vac in some standards for touch safety and selv I think.
A relay based delay on the 5VAC heater for the B+ rectifier would be appropriate if you can set the timer to align with the startup of conduction of the output stage valves. If the timer is too long, then you have to ensure the B+ rectifier can cope with the hot-start peak current from the power supply caps as well as the amp loading.
I set up a voltage dependant pre-load for choke input power supply use - but its got compromises too. It's quite a hassle for higher powered amps where operating B+ level is high and is used to drop down to preamp B+ supplies, as all preamp circuit B+ supply caps and inter-stage signal coupling caps would otherwise need to have circa 500V or 630V or even higher ratings in some cases. https://dalmura.com.au/static/HV%20DC%20shunt%20load.pdf
A relay based delay on the 5VAC heater for the B+ rectifier would be appropriate if you can set the timer to align with the startup of conduction of the output stage valves. If the timer is too long, then you have to ensure the B+ rectifier can cope with the hot-start peak current from the power supply caps as well as the amp loading.
I set up a voltage dependant pre-load for choke input power supply use - but its got compromises too. It's quite a hassle for higher powered amps where operating B+ level is high and is used to drop down to preamp B+ supplies, as all preamp circuit B+ supply caps and inter-stage signal coupling caps would otherwise need to have circa 500V or 630V or even higher ratings in some cases. https://dalmura.com.au/static/HV%20DC%20shunt%20load.pdf
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