H-K max practical voltage

[catalin gramada]

Hello. Have a 12au7 CF supplied at 400V (hk peak 180v). Biased at -9V in direct coupling configuration the cathodes are at 200V in respect with the ground. Have 100V available to elevate the heaters to keep h-k spot on.
Do you think may be a problem to elevate the heaters so high please ?
Note the CF heaters are supplied from separate 6.3V winding used only for CF so voltage elevation will not affect the rest of circuit which is supplied from different 6.3V rail please
So there is a practical max limit or I may raise the heater bias as much as 200V to do the hk offset none as time I use a separate heater winding please ?

[catalin gramada]

I biased the heaters at 105V and left 90V between heaters and cathode. Should be in order for 12au7/12bh7 please ?

[pdf64]

What’s the peak instantaneous cathode voltage, under max signal condition?

[catalin gramada]

Hi, 60-65Vpk.

[pdf64]

So the max instantaneous cathode voltage Vk pk is expected to be a bit over 230V, with respect to circuit common?
The 105V heater elevation should still then conform to the h-k pk of 180V limiting value

[catalin gramada]

Thanks !

[catalin gramada]

It works perfect. Was able to drive clean the outputs with 2.5Vpk with 6db feedback applied, exactly what I need it. Schem attached.Thx.