Using valve heater as load resistor. Would that work?

[tomchr]

So the cold temperature isn't an issue for any suitably chosen MOSFET unless you are using a 2N7000.

They key word here is "suitably". Also put the MOSFET on a heat sink. SOA is characterized with a die temperature of 25 ºC.

Tom

 

[kodabmx]

It also depends on what tube we're talking about...
If I connect a 6DQ6, the heater hits 5A (the current limit of the PSU) for 2 seconds before falling to 2.3A after 10 seconds.
OTOH, if I connect a 6N9S, the heaters peaks 0.9A for a split second before falling to 0.3A after under 10 seconds.

 

[kodabmx]

They key word here is "suitably". Also put the MOSFET on a heat sink. SOA is characterized with a die temperature of 25 ºC.

Tom

I generally design based on the SOA at 75°C myself...

 

[tomchr]

I generally design based on the SOA at 75°C myself...

Definitely preferred if those curves are available.

Tom