In article . com,
wrote:
I'm wondering what nasty effects i can expect, if any, for exceeding a
tube's maximum heater to cathode voltage rating. the tube is a 6072,
and it's maximum claimed voltage is +- 90v peak. i'm using one triode
as a cathode follower, and so the voltage at the cathode is gonna be
around 150v above ground. i'm running AC on the heaters.

Depending on the tube, it could be anything from hum to premature heater
failures.

so, why not cap couple before the follower you say? well, some think
even the expensive caps sound better when driven and loaded with lower
impedances. i'm saving the cap for the follower's output.

So, raise the heater reference voltage. Hang the heater at +150V.

i'm actually modifying an existing mic pre, and one thing they did that
i don't understand is they return each side of the AC heater supply to
ground with a 1k resistor. what is this done for? seems like if it
were left floating, i wouldn't have to worry about the voltage limit
situation. it probably also causes ground to wiggle a tiny bit at
60hz.

The heater will induce more hum if it's left floating. The heater
circuit needs to be referenced to ground. It could be referenced
to something above ground, if need be.

Or you could use a different tube for the output stage.
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."