DC elevated heaters

[C Moore]

When you have an amp that has tubes with 70-140 Volts on the Cats (like with a CF or phase inverter) how does that effect the use of elevated heaters.?
I usually see it done in a Cat Biased amp, where there might be 10-20 Volts available fro the power tube cats.
So what happens with the tubes that have a lot of voltage on their cathodes.?
Thank You

[Colossal]

With a cathode biased amp, the freebie is being able to tap off the power tubes' cathode for a DC elevation voltage. But that 10-20V may not be enough. In the case of a Plexi or amp with >100VDC on the cathode follower, I always install a dedicated voltage divider and cap to provide well filtered 60-70VDC for heater elevation. Heater elevation reduces the stress on the cathode follower tube as well as makes for quiet amps.

[C Moore]

That is kind of what I figured.....Thanks.
How much voltage do you guys think a heater can take...if you were just testing form 60Hz hum...and you had a 9 VDC (not a 6-7 Volt supply) supply. Is that more than Heaters can handle.?
Thank You

[Kagliostro]

Use a resistor to drop the voltage to the correct level, 9v is high for heaters

K

[cbass]

Yes 9 volts is way to high 4 diodes in series should drop the voltage and give you close to 6.3v

[C Moore]

Yes, diodes would work great...or a resistor. The current is not much for a few pre-tubes.
Thanks