[morzh]

Bradley

I will repeat:

1. the filaments will come up first ANYWAY. You do not need to sequence them.
Because for the high voltage to appear across the tubes first the rectifier tube needs to start conducting. And it is a tube, so it will wait for its filament to heat up before it conducts. So even if there is some short period of high voltage appearing across the rest of the tubes before they are fully heated, due to some differences in heating timing between the rectifier and the rest of them, it will be extremely short.
The whole idea is that the rectifier tube is a tube and as such behaves the same way the other tubes do, so whereas the heaters' voltage appears immediately on all the tubes (transformer acts instantly) the high voltage only appear AFTER the rectifier tube is warm and this is about THE SAME TIME when all other tubes are warm.


2. MOV (Metal oxide varistor) is NOT design to be used as a voltage limiter on a regular basis - its life is limited and then it fails, and it is not guaranteed that it fails open. You can use a transorb (a semiconductor device), but again - it will limit it PERMANENTLY. It will not delay anything.

3. If you simply want to limit the voltage from surges, then an MOV usually preceded by a fuse.

4. You can use an NTC thermistor to limit inrush if you want.
5. All this in tube radios is absolutely unnecessary.

6. Last. There are portable tube radios where the filaments are serialized and then a capacitor is used toi smooth the various groups of filaments. This is where a Zener is highly recommended in case of a blown tube so the rest does not blow. Such as in portable Zenith 6G001 and such.