Biasing a Bogner Shiva EL34

[djpatb]

I know this has been mentioned on here before, but I never really found a clear answer.
I'm biasing my EL34 Bogner Shiva with my Bias Rite. Plate volts read 550, so I should set it around 31ma...Bogner recommended 29ma. Ok, cool.
But at idle it's only reading 18ma. Bogner says to run a signal through it for a few mins to get the tubes cooking, then set to 29ma.
When I play through it, it doesn't just drift slightly, but it shoots up to 75ma!
It moves all over the place, so I'm trying to figure out under what conditions to set it at 29ma?
Or does anyone suggest a lower setting for this amp at idle with the volume turned down?
Thanks.

 

[311boogieman]

I was always told to never run a signal through the amp when trying to bias.

What I do tell people is to bias using your ear.

So you've got the amp set at 29mA. Great. Now disconnect the probe and play the amp. How does it sound?

I have a similar amp and run it just slightly hotter than you do AND my plate voltage is lower than yours. I also now use a Weber single probe because I burned out my Eurotubes probe because I probably played my guitar through the amp while the probe was plugged in.

 

[glip22]

I would go no higher than 28. EL34's cannot take that much PV on the screens which is what the worry is. If the tubes are cold bias to about 23. Jam for a few and recheck at idle, master volume off. Once the tubes are hot make sure they read 28 on the tube that draws more current. The second tube could be 26 or so.