valve Amp "Standby"

[HTH AMPS]

just out of interest, how does a DC elevated filament supply help reduce (protect against) arcing in a cathode follower?

I thought the arcing was caused by the cathode being at ground potential for a split second when the CF grid get the blast of HT, and the arc is from grid to cathode. I thought the protection against it is to add a resistor and diode in series between the grid and the cathode of the follower. I didn't know different filament supplies made a difference.

you're reducing the heater-cathode voltage (180v design max) to within its safe limits - most amps with a cathode follower are pushing the design spec limits here, but the majority of ECC83s/12AX7s cope with it.

I use DC elevated heaters on everything now, its simple, gets rid of any hum and makes the amp more reliable - whats not to like.

[jpfamps]

just out of interest, how does a DC elevated filament supply help reduce (protect against) arcing in a cathode follower?

I thought the arcing was caused by the cathode being at ground potential for a split second when the CF grid get the blast of HT, and the arc is from grid to cathode. I thought the protection against it is to add a resistor and diode in series between the grid and the cathode of the follower. I didn't know different filament supplies made a difference.

you're reducing the heater-cathode voltage (180v design max) to within its safe limits - most amps with a cathode follower are pushing the design spec limits here, but the majority of ECC83s/12AX7s cope with it.

I use DC elevated heaters on everything now, its simple, gets rid of any hum and makes the amp more reliable - whats not to like.

Absolutely.

If the cathodes are cold, neither the CF nor the preceeding valve stage will conduct current.

Thus if you turn the HT on then there will be no voltage drop across the plate load of the triode preceeding the CF ie the full B+ will be imposed in the CF grid, and this can cause arcing. Merlin Blencowe's arc protection circuit prevents this.