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Post subject: Biasing?
Posted: Thu Feb 10, 2011 5:10 pm
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How do I bias a Fender Hot Rod Deville 212 III? I need to replace tubes and I learned that I need to bias everytime I replace tubes. Yes I am very new to tube amps. VERY. Is there any guide or primer I could read about? I am aware of how dangerous It can be but I have to learn to do it because right now Im so broke it hurts lol. What tools will I need? Any help will be appreciated! Thanks!


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Post subject: Re: Biasing?
Posted: Thu Feb 10, 2011 6:56 pm
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Unless your Deville is different from the one I used to own no bias adjustment is possible without the use of a soldering iron. It is a fixed bias amp. If you use a matched set of Groove Tubes you shouldn't have any problem just plugging them in and playing it as is. Mine came with 5881s which is a military style tube in the 6L6 family. I don't know if they all came equipped that way. I suggest you use a set of regular 6L6s. Talk to your local Fender shop. They should have a matched set in stock. Or you could spend the big bucks and get a matched set of NOS RCA Black Plates online and break out the soldering iron or pay someone to bias it for you.

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Post subject: Re: Biasing?
Posted: Thu Feb 10, 2011 7:49 pm
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Both the HRDx and the Deville have a bias pot! Remove back panel and look! Get schematic from Fender and it will tell you how to set it with the test point!

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Post subject: Re: Biasing?
Posted: Thu Feb 10, 2011 10:53 pm
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BMW-KTM wrote:
Unless your Deville is different from the one I used to own no bias adjustment is possible without the use of a soldering iron. It is a fixed bias amp. If you use a matched set of Groove Tubes you shouldn't have any problem just plugging them in and playing it as is. Mine came with 5881s which is a military style tube in the 6L6 family. I don't know if they all came equipped that way. I suggest you use a set of regular 6L6s. Talk to your local Fender shop. They should have a matched set in stock. Or you could spend the big bucks and get a matched set of NOS RCA Black Plates online and break out the soldering iron or pay someone to bias it for you.


Yeah, no. The HRDv 212 I had was fully biasable.

Here's a link on exactly how to bias these amps:
http://www.eurotubes.com/euro-Fender-HRDV.htm

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Post subject: Re: Biasing?
Posted: Fri Feb 11, 2011 12:28 am
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Hi Windex1129,

You'll just need a volt meter and a small flat blade screwdriver. First know if you use 30 watt output tubes, or 25 watt. Next, measure and note the Plate voltage, it should be around 485 volts DC. Then measure and note the test point voltage in millivolts (mV), which will vary by adjusting the bias pot. You need to know both readings to calculate the idle wattage.

To measure the Plate volts, put the negative lead of your meter in one of the chassis screw holes and leave it there touching the chassis ground for all of the measurements, then touch the positive lead of your meter to "CP20" (on schematic, not marked on the board), which is where the brown wire from the output transformer connects to the underside of the tube socket circuit board. You can use the solder connection of CP20, (which is facing upward), for a test point to put your positive meter lead on. You can also check the B+ voltage at the positive side of capacitor C31 on the main board, it will be roughly the same as the Plate voltage.

Find the test point on the left corner of the tube socket circuit board at the bottom of the chassis, this is where you will measure DC mV while adjusting the bias pot, the test point is labeled "Bias Test Point" on the board. The bias pot is the blue round pot in the middle of the main circuit board, near the bottom edge. To set the test point volts, put the positive lead of the meter to the test point and adjust the bias pot to the desired setting.

Take the mV reading at the test point, divide it by two, subtract 5 mV, then multiply that number by the Plate volts to find the idle dissipation wattage. Example, a reading of 72 mV (.072 volts) at the test point and 485 Plate volts would be; reading divided by two (.072/2 = .036), subtract 5 mV (.036 - .005 = .031), multiply that number by the Plate volts for the idle wattage (.031 x 485 = 15 watts idle). Usually, it's desirable to set the idle between 50% and 70% of the tubes rated watts. For a 30 watt tube, 15 watts is 50%, 21 watts is 70%. For 25 watt tubes, 12.5 watts is 50%, 17.5 watts is 70%, etc.

If your Plate volts are roughly 485 volts, and you use 30 watt tubes, you'll probably set the test point reading to between 72 mV and 96 mV (50% to 70% of tubes rating), depending on whether you want your bias cold or hot.

HRDvl schematic
http://support.fender.com/schematics/guitar_amplifiers/Hot_Rod_DeVille_schematic.pdf

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Post subject: Re: Biasing?
Posted: Fri Feb 11, 2011 5:07 am
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First thing you should do is learn about amp safety. In order to bias the amp it has to be on, be careful in there.

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Post subject: Re: Biasing?
Posted: Fri Feb 11, 2011 6:13 am
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Here's how it's done. It's easy, just be careful and don't wear ANY jewelry.

http://www.eurotubes.com/euro-Fender-HRDV.htm

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Post subject: Re: Biasing?
Posted: Fri Feb 11, 2011 12:22 pm
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Hmmm. Mine was a Blues Deville, not a Hot Rod. I thought they were essentially the same. Maybe there was a model year issue in there somewhere?

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Post subject: Re: Biasing?
Posted: Fri Feb 11, 2011 1:48 pm
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BMW-KTM wrote:
Hmmm. Mine was a Blues Deville, not a Hot Rod. I thought they were essentially the same. Maybe there was a model year issue in there somewhere?


No model year issue. The first generation Blues Deluxe/Deville were replaced by the Hot Rod Deluxe/Deville in the mid-late 90's and are related but definately not the same. The first gen Blues did not have a bias pot, the Blues "reissues" that came out a few years ago have a bias pot. The Hot Rods always had a bias pot.

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Post subject: Re: Biasing?
Posted: Fri Feb 11, 2011 3:15 pm
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OK, Thanks. For a second there I thought I was going nuts cuz I knew mine didn't have one.

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Post subject: Re: Biasing?
Posted: Fri Feb 11, 2011 9:57 pm
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Well, actually it is a model year issue. The very first BDlx and BDvl version did not have a bias adjust, the second generation of BDlx and BDvl did have a bias adjust, those with the adjustment were called reissues (and if I remember correctly they didn't have an external speaker jack on the originals either). The HRDlx and HRDvl have always had a bias adjust, even the first generation. :idea:

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