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Old 13th February 2012, 05:20 PM   #1
Atom66 is offline Atom66  Canada
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Default Quicksilver 8417 Bias

Hi
Anyone have a schematic of how to add dual bias pots to the Quicksilver 8417?
Thanks
Andrew
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Old 13th February 2012, 10:10 PM   #2
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Its very simple. I did it this way... I removed the 1/4" jack. I took the transformer CT wires to ground. I removed the wire that connected the two output tubes on pin number 8. I installed a 10 ohm 1watt resistor from pin 8 of each output tubes to ground.

I found the two grid resistors connection at the center terminal of the bias pot and removed the left resistor from the center connection of the pot and soldered a wire onto it. I installed another pot where the 1/4" jack was. I soldered the grid resistor wire to the center connection (the out of the pot). I soldered a cap from the center terminal of the pot that was added to ground. (Just like the other side) I paralleled the ground terminal of the original pot to the pot I added. I paralleled a wire from the in connection of the original pot to the pot I added. Note* Looking at the back of the pot as it is installed in the chassis is on the left ground, center is out, right terminal is in.

Now I added 3 turret terminal test points to the chassis. One black goes to power supply ground. One red goes to the #8 pin of one of the output tubes socket. The other red test point is connected to the number 8 pin of the other output tube.

I changed my bias circuit as follows I removed the resistor (10K) that is connected to the bias diode and replaced it with a 1K resistor. I replaced the original bias cap (60mfd/150vdc) with a 100/150vdc and I replaced the cap 220/63 with 100/100
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Last edited by Original Burnedfingers; 13th February 2012 at 10:20 PM.
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Old 14th February 2012, 01:43 PM   #3
Atom66 is offline Atom66  Canada
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Thanks for your help!
Andrew
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Old 14th February 2012, 01:57 PM   #4
Atom66 is offline Atom66  Canada
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Join Date: Oct 2003
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Another question .Will this work with 6550s as well as 8417?
Thanks
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Old 14th February 2012, 09:24 PM   #5
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If you change the grid resistors so that you can run most of the 8417's out there the amp will bias up and run fine with what ever you choose to put in it output tube wise. I run 6550's at about 40mA a tube. I run KT88's a lot hotter. If I were you I would put the 8417 back on the shelf and let them sit.

PM me if you have any questions.
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