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Post subject: How to Bias?
Posted: Sat May 22, 2010 1:09 pm
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As in which pins on the tubes. And anything else you care to add on biasing a 90s Blues Deluxe. I'm realizing as I type that you must have to mod the amp first so there is something to adjust! Or is there already a variable resistor somewhere and I'm missing it? Maybe there is a bias mod to be had for the Blues Deluxe like the HRDx series has. Can anyone help. I read the previous thread. It did mention the word biasing alot. I bet the search engine loves that thread. It just has no information on how you do it.

Thanks

Ron


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Posted: Sat May 22, 2010 1:22 pm
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http://www.eurotubes.com/euro-Fender-HRDV.htm


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Posted: Sat May 22, 2010 2:11 pm
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joncarr1979 wrote:
http://www.eurotubes.com/euro-Fender-HRDV.htm

+1

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Post subject:
Posted: Sat May 22, 2010 3:34 pm
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It's easy to confuse these two amps. My question is about biasing a Blues Deluxe not the Hot Rod amps. The deluxe does not have a bias trim pot. The thing I probably need it the points on the tube pins which he didn't go into. But he did advocate setting the tubes pretty hot. He gets his tubes alot cheaper than we do. I don't know what the other meter was Usually to measure amps or milliamps you need a series connection in the circuit. Much more of a p i t a since it means unsoldering and re soldering wires.

Ron


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Posted: Sat May 22, 2010 5:15 pm
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Blues Deluxe don't have trim pot to adjust bias.

You have to change a resistor to modify the bias or put a trim pot
You have to know what you are doing before do that work.
Tubes amps have high voltage that can kill you.

The multimeter, read voltage on the test point on a 1 ohms resistor and you convert in milliamp: 1 ohm resitor with 1 millivolt = 1 milliamp. 1 ohm with 2 millivolts =2 milliamp, etc
This read the current of the 2 tubes

Meters on tube are Bias Probe, they read current on each tube.

If you play loud better bias colder than hot. But if you play low volume little bit hot is good.


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Posted: Sat May 22, 2010 7:13 pm
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The bias resistor is R87. Presently it is 27K ohms. Depending on the tubes, usually you go down in resistance since the 90's USA Blues Deluxe is biased cold. You can measure the resistance on your output transformer red and blue wires, and then the same red and the brown wire, Of course do this powered down, unplugged from wall outlet, etc. Once you get that resistance, fire the thing up, let it warm up, and measure the voltage drop across these points. Use Ohms law to figure your current. Red and blue is one tube, red and brown is the other. If you are unfamiliar with a multimeter or Ohms law, take it to a tech, as these voltages are 400+ in this amp and will kill you!


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