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Post by rvf263 on Nov 28, 2013 11:58:24 GMT -7
Happy Thanksgiving to all,
I'm new to the KT45 and have a question about biasing.
On the Dr. Z website it has the KT45 under the "Fixed Bias" list.
I read other threads talking about biasing the KT45.
I called Dr. Z and the guy said yes, the KT45 does need biased.
I'm confused, I thought "Fixed Bias" means the tubes don't need biased.
Can someone please explain the different types of biasing, and the type the KT45 requires?
Thanks!
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Post by doctorice on Nov 28, 2013 12:07:18 GMT -7
Sorry, I'm not sufficiently up on this to explain, but there are folks here who can and, it is hoped, will.
However, I can state that some Z amps are "self biasing", meaning you don't need to tweak the bias after changing power tubes. Other Zs have user-adjustable biasing; with these the bias needs to be checked and possibly adjusted when power tubes are replaced. The KT-45 falls in the latter category.
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Post by bluzman on Nov 28, 2013 13:00:54 GMT -7
Yeah... many get confused with the "fixed bias" terminology. Here's how I remembered it so as to avoid confusion in my own head: "Fixed Bias" means the bias needs to be fixed or adjusted via the bias potentiometer. "Cathode Bias" (also known as Self Biasing) is done via resistors in the circuit there is no biasing pot. Always use a good balanced set of tubes. Dr. Z Amps fixed biased amps are Z-28, EZG-50, KT-45, SRZ-65, Galaxie and Route 66 the others are cathode biased. www.drzamps.com/bias_notes.htmlSo if you ever have Remedy, JAZ or an EL84 Z-Amp and the guy at the store tells you it needs to be biased, then find another store to deal with.
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Post by Deleted on Nov 28, 2013 17:59:21 GMT -7
Fixed bias just means that the output tubes are being manual set and left at the optimum mA setting for safe operation. Each set of tubes may have a different optimum mA setting. So when you replace output tubes in a fixed bias amp you should check and possibly set the new tubes at a safe operating level.
Cathode bias amps use resistors and such to preset a safe range for the tubes to run in. That way you can usually grab any good tube and throw it in the amp and it will work just fine.
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Post by Deleted on Nov 28, 2013 18:00:53 GMT -7
Yeah... many get confused with the "fixed bias" terminology. Here's how I remembered it so as to avoid confusion in my own head: "Fixed Bias" means the bias needs to be fixed or adjusted via the bias potentiometer. "Cathode Bias" (also known as Self Biasing) is done via resistors in the circuit there is no biasing pot. Always use a good balanced set of tubes. Dr. Z Amps fixed biased amps are Z-28, EZG-50, KT-45, SRZ-65, Galaxie and Route 66 the others are cathode biased. www.drzamps.com/bias_notes.htmlSo if you ever have Remedy, JAZ or an EL84 Z-Amp and the guy at the store tells you it needs to be biased, then find another store to deal with. ▲▲▲ Like
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Post by rvf263 on Nov 28, 2013 18:05:17 GMT -7
Hey doctorice, bluzman, and doc001,
Thanks for responding and helping me out, I think I can keep it straight in my head now.
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Post by markT on Nov 28, 2013 18:21:12 GMT -7
Yeah... many get confused with the "fixed bias" terminology. Here's how I remembered it so as to avoid confusion in my own head: "Fixed Bias" means the bias needs to be fixed or adjusted via the bias potentiometer. "Cathode Bias" (also known as Self Biasing) is done via resistors in the circuit there is no biasing pot. Always use a good balanced set of tubes. Dr. Z Amps fixed biased amps are Z-28, EZG-50, KT-45, SRZ-65, Galaxie and Route 66 the others are cathode biased. www.drzamps.com/bias_notes.htmlSo if you ever have Remedy, JAZ or an EL84 Z-Amp and the guy at the store tells you it needs to be biased, then find another store to deal with. ^^^ What he said.....EVERYTHING he said!!
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Post by thatstatuemoved on Apr 21, 2014 18:00:52 GMT -7
Yeah... many get confused with the "fixed bias" terminology. Here's how I remembered it so as to avoid confusion in my own head: "Fixed Bias" means the bias needs to be fixed or adjusted via the bias potentiometer. "Cathode Bias" (also known as Self Biasing) is done via resistors in the circuit there is no biasing pot. Always use a good balanced set of tubes. Dr. Z Amps fixed biased amps are Z-28, EZG-50, KT-45, SRZ-65, Galaxie and Route 66 the others are cathode biased. www.drzamps.com/bias_notes.htmlSo if you ever have Remedy, JAZ or an EL84 Z-Amp and the guy at the store tells you it needs to be biased, then find another store to deal with. thanks for that tip on remembering the bias--I always got the two confused.
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