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Post subject: 1973 Twin Bias addition
Posted: Mon Oct 26, 2009 11:38 am
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hey Floks,

Does anyone have a good schematic , or drawing to add a bias control to my 1973 Twin? Also where exactley is the bias resistor?

Thanks, Tom


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Posted: Mon Oct 26, 2009 12:50 pm
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Tom, try here. Tons of info and schematics.
http://www.ampwares.com/fender.asp


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Posted: Mon Oct 26, 2009 12:54 pm
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63supro wrote:
Tom, try here. Tons of info and schematics.
http://www.ampwares.com/fender.asp


Thanks. I'll take a look.


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Posted: Tue Oct 27, 2009 6:56 pm
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Hi Tom, the Silverface to Blackface bias circuit conversion requires a number of steps concerning component replacement, removal, and reconfiguration. I've done a handful of these, over the years, and use two books as resources:"A Desktop Reference of Hip Vintage Guitar Amps" by Gerald Weber;"The Tube Amp Book" by Aspen Pittman. I'm an old guy and hard copy suits me, but you'll probably be able to find a source of info on the net. Checked out a few sites, but no luck. You might try to contact www.torresengineering.com. They used to offer a kit, but I didn't see it on their site. Maybe the computer savvy guys can be of more help. ART

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Posted: Wed Oct 28, 2009 5:50 am
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Thanks for the help. From all I've seen it seems to be an easy mod, but most I've seen are different. So I'm just trying to find a good fix.

Thanks again, Tom (I'm old too)


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Posted: Thu Oct 29, 2009 7:30 pm
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Hey Tom, just wondering how you plan to measure the bias in your Twin. The transformer shunt method or the cathode resistor method? I used the shunt method for years, setting up two Fluke meters so I could quickly check the plate volage and the current. But about 10 months ago I bought the Weber Bias Rite, and man is that a great tool(meter). Way safer and a lot less hassle, don't even need to pull the chassis on the old combos. ART

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Posted: Sun Nov 01, 2009 2:26 am
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I also find some good stuff on fixed bias mods on:
www.hoffmanamps.com


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