Bogner headshells: do they effect bias level?

[TheMagicEight]

I use a Bias Rite when setting levels, which means my amps are always out of the shell when working. Has anyone noticed if they run a little hotter when in the headshell? I'd imagine they do; just wondering if that's what I'm hearing and I need to drop my bias levels down or if it's maybe something else. After a little while of playing, my bass response gets a little flabbier and mids aren't as punchy. Any similar experiences? This is starting to seem obvious now that I've written it down....

 

[RockStarNick]

I've heard this is very common to most EL34s. They change after playing for quite a while.

Everyone keeps raving about "cranking the bias up", but I've had more and more consistent tone from my Bogners by keeping the bias at a medium-to-conservative level. Not to mention longer tube life.

 

[TheMagicEight]

I've heard this is very common to most EL34s. They change after playing for quite a while.

Everyone keeps raving about "cranking the bias up", but I've had more and more consistent tone from my Bogners by keeping the bias at a medium-to-conservative level. Not to mention longer tube life.

That's what I'm finding too. I biased a little cold a few days back. Did a 12hr recording session with the Ecstasy on Thursday and it kicked ass start to finish!

 

[steve_k]

Two things cause this....

1) The bias resistors heat up. Since they are generally under the the chassis fairly close to the power tubes, over time they get pretty warm.

2) The tubes heat and expand, especially new tubes. The chemicals on the plates react as well. This is why some tube shops will advertise a burn in process. As they heat up, the vacuum inside becomes less negative and affects the movement of electrons from positive to negative impacting current flow.

You can easily do your own burn in. Put in a new set of tubes, bias them up, then leave the amp running about 8 hours. Come back and rebias.

Steve