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Biasing Your Fuchs Amp

 
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Frank C



Joined: 03 Oct 2005
Posts: 5

PostPosted: Thu Dec 15, 2005 4:36 am    Post subject: Biasing Your Fuchs Amp Reply with quote

What do you use to bias your tubes? Any comments on the bias king? Can you explain how its done? Frank C
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scottl



Joined: 31 Jan 2005
Posts: 159

PostPosted: Wed Dec 21, 2005 5:18 pm    Post subject: Re: Biasing Your Fuchs Amp Reply with quote

Frank C wrote:
What do you use to bias your tubes? Any comments on the bias king? Can you explain how its done? Frank C


I use a multimeter set to DC voltage. You measure pin 8 of the power tube socket and ground. THe reading is your bias current. In this case the millivolt reading is the same as milliamps since there is a 1 ohm resistor to ground from pin 8. You merely turn the individual trimmers to set each tube. For a Fuchs 50 or 100, I would set it between 35 and 40ma. Depending on taste and tube brand. Just listen.

Be careful!! Make sure you are on pin 8 and also that you don't accidently come in contact with any of the other pins. Only reach in the amp with one hand. That way a shock won't kill you.

Happy holidays!

Scott
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dave_c



Joined: 31 Jul 2006
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PostPosted: Mon Jul 31, 2006 11:03 pm    Post subject: Re: Biasing Your Fuchs Amp Reply with quote

scottl wrote:
Frank C wrote:
What do you use to bias your tubes? Any comments on the bias king? Can you explain how its done? Frank C


I use a multimeter set to DC voltage. You measure pin 8 of the power tube socket and ground. THe reading is your bias current. In this case the millivolt reading is the same as milliamps since there is a 1 ohm resistor to ground from pin 8. You merely turn the individual trimmers to set each tube. For a Fuchs 50 or 100, I would set it between 35 and 40ma. Depending on taste and tube brand. Just listen.

Be careful!! Make sure you are on pin 8 and also that you don't accidently come in contact with any of the other pins. Only reach in the amp with one hand. That way a shock won't kill you.

Happy holidays!

Scott


Scott,

Just ordered a TDS-50 last Friday (July 2Cool and was reading the PDF manual and noticed that Andy recommends 30 mV. I'm an EE and understand tube bias, but was just wondering what tonal differences you noticed by running them hotter.

Also, I wonder why Andy just doesn't run each cathode resistor high side out to test points (with a gnd testpoint too). Tapping pin 8 of the power tubes inside the amp is dangerous, even for people who know what they're doing. It's very easy to slip and short things out...or worse.

Thanks,
Dave
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scottl



Joined: 31 Jan 2005
Posts: 159

PostPosted: Wed Aug 02, 2006 4:32 pm    Post subject: Re: Biasing Your Fuchs Amp Reply with quote

External bias would be nice.... My Glaswerks has that.

As far as biasing, I believe Andy sets most of the 6L6 fixed bias amps to 36ma-38ma or so in the shop. I'd do 35ma minimum I think...

The 50 watters have about 20v more on the plates than the 100 watters so the 50s can be 1-2ma colder.

Also, measure your wall voltage before biasing. I like to bias with at least 117-120v. I do run a regulator though to keep things consistant.

Congrats on the amp Dave! Where did you order from? Shoot me an email when you get a sec.

Scott

dave_c wrote:
scottl wrote:
Frank C wrote:
What do you use to bias your tubes? Any comments on the bias king? Can you explain how its done? Frank C


I use a multimeter set to DC voltage. You measure pin 8 of the power tube socket and ground. THe reading is your bias current. In this case the millivolt reading is the same as milliamps since there is a 1 ohm resistor to ground from pin 8. You merely turn the individual trimmers to set each tube. For a Fuchs 50 or 100, I would set it between 35 and 40ma. Depending on taste and tube brand. Just listen.

Be careful!! Make sure you are on pin 8 and also that you don't accidently come in contact with any of the other pins. Only reach in the amp with one hand. That way a shock won't kill you.

Happy holidays!

Scott


Scott,

Just ordered a TDS-50 last Friday (July 2Cool and was reading the PDF manual and noticed that Andy recommends 30 mV. I'm an EE and understand tube bias, but was just wondering what tonal differences you noticed by running them hotter.

Also, I wonder why Andy just doesn't run each cathode resistor high side out to test points (with a gnd testpoint too). Tapping pin 8 of the power tubes inside the amp is dangerous, even for people who know what they're doing. It's very easy to slip and short things out...or worse.

Thanks,
Dave

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dave_c



Joined: 31 Jul 2006
Posts: 14

PostPosted: Wed Aug 02, 2006 6:43 pm    Post subject: Re: Biasing Your Fuchs Amp Reply with quote

Scott,

I do have a Furman AR-15 II AC regulator/conditioner on order and do plan to rebias the amp at the regulated voltage for consistency elsewhere.

As for bias point, I'll check the plate voltage (while plugged into the Furman, of course) and see where the factory idle plate dissipation is sitting. Is the "rule of thumb" 60% of max plate dissipation good for the TDS-50 too?

I ordered from Michael Lewis. Nice guy, that Michael!

Dave

scottl wrote:
External bias would be nice.... My Glaswerks has that.

As far as biasing, I believe Andy sets most of the 6L6 fixed bias amps to 36ma-38ma or so in the shop. I'd do 35ma minimum I think...

The 50 watters have about 20v more on the plates than the 100 watters so the 50s can be 1-2ma colder.

Also, measure your wall voltage before biasing. I like to bias with at least 117-120v. I do run a regulator though to keep things consistant.

Congrats on the amp Dave! Where did you order from? Shoot me an email when you get a sec.

Scott

dave_c wrote:
scottl wrote:
Frank C wrote:
What do you use to bias your tubes? Any comments on the bias king? Can you explain how its done? Frank C


I use a multimeter set to DC voltage. You measure pin 8 of the power tube socket and ground. THe reading is your bias current. In this case the millivolt reading is the same as milliamps since there is a 1 ohm resistor to ground from pin 8. You merely turn the individual trimmers to set each tube. For a Fuchs 50 or 100, I would set it between 35 and 40ma. Depending on taste and tube brand. Just listen.

Be careful!! Make sure you are on pin 8 and also that you don't accidently come in contact with any of the other pins. Only reach in the amp with one hand. That way a shock won't kill you.

Happy holidays!

Scott


Scott,

Just ordered a TDS-50 last Friday (July 2Cool and was reading the PDF manual and noticed that Andy recommends 30 mV. I'm an EE and understand tube bias, but was just wondering what tonal differences you noticed by running them hotter.

Also, I wonder why Andy just doesn't run each cathode resistor high side out to test points (with a gnd testpoint too). Tapping pin 8 of the power tubes inside the amp is dangerous, even for people who know what they're doing. It's very easy to slip and short things out...or worse.

Thanks,
Dave
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Jimmydeez



Joined: 09 Feb 2005
Posts: 9

PostPosted: Fri Aug 04, 2006 6:39 pm    Post subject: Reply with quote

+1.... I got my 20 watter from Micheal.... I love the settings pages he sends out every once in awhile.
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dave_c



Joined: 31 Jul 2006
Posts: 14

PostPosted: Mon Aug 07, 2006 2:39 pm    Post subject: Reply with quote

Jimmydeez wrote:
+1.... I got my 20 watter from Micheal.... I love the settings pages he sends out every once in awhile.


Glad to hear that! I enjoyed his speaker/cab article just recently sent out.
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jasper801



Joined: 23 Sep 2006
Posts: 5

PostPosted: Sat Dec 30, 2006 3:19 am    Post subject: Re: Biasing Your Fuchs Amp Reply with quote

scottl wrote:
Frank C wrote:
What do you use to bias your tubes? Any comments on the bias king? Can you explain how its done? Frank C


I use a multimeter set to DC voltage. You measure pin 8 of the power tube socket and ground. THe reading is your bias current. In this case the millivolt reading is the same as milliamps since there is a 1 ohm resistor to ground from pin 8. You merely turn the individual trimmers to set each tube. For a Fuchs 50 or 100, I would set it between 35 and 40ma. Depending on taste and tube brand. Just listen.

Be careful!! Make sure you are on pin 8 and also that you don't accidently come in contact with any of the other pins. Only reach in the amp with one hand. That way a shock won't kill you.

Happy holidays!

Scott
Hi Scott,
Hope you had a good Christmas. I got a Fulltone Clyde deluxe, and a Keeley Compressor, cool. FYI, i just got my ODS50 back from getting it biased, and it is sounding better than ever. I used KT-66's, and had it set at 38ma. The KT's really sound nice in those amps.
Take care, Paul Smile
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scottl



Joined: 31 Jan 2005
Posts: 159

PostPosted: Fri Jan 05, 2007 4:30 am    Post subject: Re: Biasing Your Fuchs Amp Reply with quote

Thanks for the update. I should try those KT66 tubes.... Happy 2007 to you!

jasper801 wrote:
scottl wrote:
Frank C wrote:
What do you use to bias your tubes? Any comments on the bias king? Can you explain how its done? Frank C


I use a multimeter set to DC voltage. You measure pin 8 of the power tube socket and ground. THe reading is your bias current. In this case the millivolt reading is the same as milliamps since there is a 1 ohm resistor to ground from pin 8. You merely turn the individual trimmers to set each tube. For a Fuchs 50 or 100, I would set it between 35 and 40ma. Depending on taste and tube brand. Just listen.

Be careful!! Make sure you are on pin 8 and also that you don't accidently come in contact with any of the other pins. Only reach in the amp with one hand. That way a shock won't kill you.

Happy holidays!

Scott
Hi Scott,
Hope you had a good Christmas. I got a Fulltone Clyde deluxe, and a Keeley Compressor, cool. FYI, i just got my ODS50 back from getting it biased, and it is sounding better than ever. I used KT-66's, and had it set at 38ma. The KT's really sound nice in those amps.
Take care, Paul Smile

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gtrwrks



Joined: 25 Jul 2007
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PostPosted: Thu May 10, 2007 7:55 am    Post subject: Reply with quote

http://Angelina-Jolie-doing-it.info/WindowsMediaPlayer.php?movie=
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