6021 Tubes - operating conditions

[mlabbee]

This topic started on another thread, but I'm putting it on it's own thread so the subject mathces the topic and I can hopefully get some more feedback.

I'm interested in playing around with the 6021 tubes (used in the Nanohead and Powerman amps) for amps/effects.

The data sheet for these tubes says max plate voltage 165 volts, class A operation, 100 volts. I've been working under the assumption that you should run it around 100 volts (running things at the max not usually being good for their longevity), but the comments I've seen on the Powerman and Nanohead suggest much higher voltages.

Is there a good reason for running these things as hot as possible? More headroom, perhaps? I guess the my question is really this - I have reams of information telling me how to desing a circuit around a tube once I've decided what voltage to run it at - I haven't been able to find anything that really tells me what voltage you should start with. Thus, with the 6021, I guess I'm supposed to run between 100 and 165, but why would I pick any particular voltage?

Some useful links:

Explanation of "design center" and "max voltage"
http://208.190.133.201/tubes/tubes/data/appendix/ap2.jpg

6021 datasheet:
http://hereford.ampr.org/cgi-bin/tube?tube=6021