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Post by Jerry P on May 20, 2004 11:42:45 GMT -5
EDIT: Sorry guys, I had to take down the bias mod info. Too many people were doing the mod themselves and then listing the amps on Ebay as being modded by FJA Mods. I can't have anyone buying amps they think I worked on and having problems. I don't desrve any bad press for work I didn't perform. Jerry
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Post by Chris Nuccio on May 21, 2004 2:46:10 GMT -5
Good, detailed description Jerry! Thanks for the info. ;D
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Post by gunter on May 28, 2004 17:51:10 GMT -5
thanks ive been looking for a good description everywere
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Post by JerryP on May 29, 2004 23:55:50 GMT -5
Thanks guys! I'm glad you found it useful. Jerry
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Post by ghubbell on May 30, 2004 23:59:35 GMT -5
AWESOME!!! Thanks!!! ;D
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Post by ghubbell on Jun 3, 2004 9:15:55 GMT -5
WOW! WHAT A DIFFERENCE!!! Forget the pot, just use the 5.1k resistor!
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Post by Jerry P on Jun 19, 2004 22:46:57 GMT -5
WOW! WHAT A DIFFERENCE!!! Forget the pot, just use the 5.1k resistor! I wouldn't do it without the pot. It might be biased too hot. Make sure your monitoring your bias to be sure your not hurting your tubes or amp. Jerry
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Post by Bill on Aug 1, 2004 0:10:07 GMT -5
Hi! I just have a quick question. Is it a bad idea to extend the trim pot up to the chassis surface? Maybe use longer wire. Also drill a small hole in the chassis where you mount the trim pot from underneath? This way the amp doesnt have to be taken apart every time to rebias? Or does the longer wire pose a threat to functionality? Thanks, Bill (sepsis311@cocmast.net
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Post by swakke on Aug 3, 2004 1:38:09 GMT -5
indeed, been thinking about that too, good question... btw how do you make sure all the caps are bleeded empty? and if they're not, how do you make 'em do it? thanx!
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Post by swakke on Aug 3, 2004 1:53:08 GMT -5
or adding a bias-meter to the amp...
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Post by Rafal on Aug 3, 2004 16:00:45 GMT -5
indeed, been thinking about that too, good question... btw how do you make sure all the caps are bleeded empty? and if they're not, how do you make 'em do it? thanx! This is what I have found Electrolytic (and other type) filter capacitors can hold lethal charges - be sure to discharge them before working on an amplifier. This can be done by connectinh the "+" side to the chassis (unless the cap is in a negative voltage supply, like the bias supply, where you must short the "-" side to the chassis), using a wire . This will make a big spark and a loud noise, which is sure to impress any onlookers. If you'd rather do it more discreetly, make a jumper cable consisting of alligator clips on the ends, with a resistor in series in the middle of the jumper. Use a value of somewhere between 10K and 100K, with a power rating of 5W or so (a high power rating is not really necessary for dissipation reasons, but mainly because the higher power resistors are physically more robust and won't tend to break). Be sure to adequately insulate the resistor with heat-shrink tubing so the wires aren't exposed, or you'll get shocked while trying to discharge the capacitors.Do I bleed the caps in the 5150 using the "+" or the "-" side before I do the mod? Thanks.
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Post by Jerry P on Aug 3, 2004 20:28:38 GMT -5
The 5150 has bleeder resistors and will bleed the voltage off by itself. Jerry
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Post by Rafal on Aug 4, 2004 1:23:52 GMT -5
The 5150 has bleeder resistors and will bleed the voltage off by itself. Jerry Thank You for answering. I did the mod myself and it came out great thanks to your info (I used same mini pot of 10k and used a glue gun to hold it in place). I got one more question if you don't mind. I noticed that in the pics you have used some glue on the leads of the cap to better protect it so it stays in place. Did you use special silicone or normal glue-gun glue to do that?
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Post by Jerry P on Aug 4, 2004 8:05:36 GMT -5
I use hot glue. Don't use silicone. Over time silicone will cause the leads to corrode and oxidize. Jerry
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Post by Bill on Aug 5, 2004 3:16:01 GMT -5
any chance on posting info on external bias test points? thanks
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