Biasing my AD30TC head

whoodt · Post by **whoodt** » Thu Apr 17, 2003 9:55 pm

Hi guys, just changed my power tubes and I was wondering if I need to get soemone to re-bias my amp? My new tubes are matched BTW.

Oh one more thing....
Even now, with new tubes, the amp is sounding harsher and less bassy than when I first bought it (1 yr ago)....one day, the volume just dropped and then came back up when I was turning up the gain. Any pointers? I am replacing all my pre-amp tubes next week, hopefully it will help. What other components in an amp like this could go wrong? Please help!!!!!

Hugh

Deadbeat Son · Post by **Deadbeat Son** » Thu May 01, 2003 4:36 am

As for the first part of your post, according to the forum admin fellow, Orange AD30 and 15 series amps are self-biasing. No need to adjust.

-JP

Davis · Post by **Davis** » Tue May 06, 2003 8:57 pm

I hate those spade connectors. I always take them off and re-solder all the connections. As far as re-biasing...even Mesa/Boogie amps, which are a "fixed bias" amp should be re'biased after tube changes. Aspen Pittman who wrote the Tube Amp Book suggests re-biasing after tube changes no matter what amp you own. I'm just repeating what I've read. It sounds like a practical idea if you want to avoid trouble down the road.

Deadbeat Son · Post by **Deadbeat Son** » Wed May 07, 2003 7:34 pm

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I hate those spade connectors. I always take them off and re-solder all the connections. As far as re-biasing...even Mesa/Boogie amps, which are a "fixed bias" amp should be re'biased after tube changes. Aspen Pittman who wrote the Tube Amp Book suggests re-biasing after tube changes no matter what amp you own. I'm just repeating what I've read. It sounds like a practical idea if you want to avoid trouble down the road.

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There is a difference between "fixed bias" and "self-biasing". Usually, a self-biasing amp is cathode-biased I believe.

-JP

Davis · Post by **Davis** » Thu May 08, 2003 4:08 pm

You're absolutely correct. Aspen Pittman observes in his book that even "fixed bias" amps can go a little out of adjustment over time, and to insure correct bias, as well as getting the optimum performance from your amp, you should check the bias.
What I'd REALLY like to see in all Orange amps, is a bias selector switch. That way you could try different tubes and experience different tones from the amp without soldering resisters under the ceramic tube holders and all that stuff.
Anyway, Sooner reports that ALL AD30 amps are self biasing....so I'm not going to worry about it at this point.

Biasing my AD30TC head

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