Ian Iveson wrote:

"Patrick Turner" wrote

RDH4 says +/- 10%. ...

Brimar says mains-derived heater voltage should be within 5% at
nominal mains voltage, as long as mains itself remains within 10%

Does that mean 15% is the limit?

I can't quote the exact reference from RDH4, but its in there alright.

And there is no mention of +/-15% afaik.

So whatever that book says is about right.

I try to make the heater voltage for all gear stay within +/- 2% of the
official proper voltage.

Mains might vary +/- 5%, but I have never seen more than
between 235v and 253v for 240v nominal, so I guess heater voltage would
vary say +/- 7%, but over time its not enough to significantly shorten
expected tube life.

One can place 12.6 volts onto a 12AX7, and gee it looks bright, but not
for very long,
and you might stuff the emission of the cathode....

The tube will also work with 8 volts on the heater, but it'll be noisy,
and Gm will be low...

Patrick Turner.






cheers, Ian