Another Tube Bias thread...

[OnlyVees]

Is there somewhere online, a step-by-step "Biasing output tubes for dummys?" I'm retubing my little Super Champ XD and I'd like to see where the factory setting is? (not physically, I know where the trim pot is inside the amp) Can this be done with a multimeter?

I'm one of those, knows enough to hurt himself/the amp types... :jo

Thanking the Collective in advance.

[FrankieSixxxgun]

http://www.duncanamps.com/technical/lvbias.html

Eurotubes has videos too:
http://www.eurotubes.com/euro-video.htm

[ohmslaw]

Is there somewhere online, a step-by-step "Biasing output tubes for dummys?" I'm retubing my little Super Champ XD and I'd like to see where the factory setting is? (not physically, I know where the trim pot is inside the amp) Can this be done with a multimeter?

I'm one of those, knows enough to hurt himself/the amp types... :jo

Thanking the Collective in advance.

I just did this with my Superchamp XD and it could not be simpler, and the amp sounded much better after retubing with JJ's and biasing.

Yes, it is done with a simple multimeter using the 200 mVDC range. Do you have a schematic? There doesn't seem to be a link to one on the Fender site but one of their customer service guys emailed me the schematic. There is a single test point for both tubes along with a standard bias pot on the PCB. I believe the setting is 40 mVDC but I don't have the info handy. Let me know how it turns out, and be careful; I just toasted a trace on my Supersonic last week (was able to easily repair it, thankfully).

[kennyramjam]

Yahoo can help. Simply enter "biasing a fender champ" and you will see lots of information available. I wanted
to bias my 50W JMP Marshall, and the net came in very handy. Remember, above all, stay safe. There are
lethal voltages that exist inside the amp that aren't automatically removed when the amp is unplugged. And
make sure the probes on any meters you use are well insulated. Having said that, the method I used to bias
my Marshall was the cathode resistor method, and I was real happy with the results. Perhaps this method
can be used on your Fender, as well. Before finding out about this method, I tried setting the bias by setting
the negative bias voltage to a set amount. This is easy to do, but when setting bias using this method, one
never knows the actual dissipation. It works better to measure plate voltage and mulitiply by tube current for
the actual wattage. When biaisng my Marshall, I used one ohm resistors which, with respect to ohm's law, allow
current to be measured as voltage. (If E=IR and R is 1, E=I, period!). There is much more on this, if you check
out the web. Here are a couple of sites.

http://www.diyguitaramp.com/bias.html

http://www.svvintageamps.com/tubebias.php