#1
I read everywhere about how important it is to bias youre powertubes, so i started to read about it, how to do it and stuff...

I learned that you use something called "trimpots" to measure the millivolts... So i open the back of my marshall head, and there it hasnt got any trimpots... So I wondered as to how i am supposed to bias my amp.. ?

Its a JCM 800 50W from the year 1983...

Thanks
Gibson Les Paul Standard
Takamine G Series 6&12 string accoustics

Marshall JCM 800 50w 1987 (4 input)
Marshall 1936 Cab

Jim Dunlop CryBaby
MXR 10 band EQ

R n'fn' R!
#2
Quote by Sl4Sh_Jr.
I read everywhere about how important it is to bias youre powertubes, so i started to read about it, how to do it and stuff...

I learned that you use something called "trimpots" to measure the millivolts... So i open the back of my marshall head, and there it hasnt got any trimpots... So I wondered as to how i am supposed to bias my amp.. ?

Its a JCM 800 50W from the year 1983...

Thanks

check out this vid at Eurotubes, it's a generic biasing vid, but he's using an 800 for the example. The "trimpot" is just a very small potentiometer, the same principle as a volume pot or a vol/tone pot on your guitar, just a lot smaller. You measure the bias current with a bias probe, or a multi meter if you know where to take measurements. Using a bias probe is much safer and easier however. You then use the trimpot to adjust how much current the tubes are drawing.

http://www.eurotubes.com/euro-Generic-Bias.htm
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
amp clips
amp vids
#3
alright, thanks!

although all this seems very complicated.... I dont have any of the measuring meters, and im from norway, so my technical english is not that well... I wish to bias my amp to get it "healthy", but im not quite sure if i have understood how... well i guess i just have to have a go at it...
Gibson Les Paul Standard
Takamine G Series 6&12 string accoustics

Marshall JCM 800 50w 1987 (4 input)
Marshall 1936 Cab

Jim Dunlop CryBaby
MXR 10 band EQ

R n'fn' R!
#4
Quote by Sl4Sh_Jr.
alright, thanks!

although all this seems very complicated.... I dont have any of the measuring meters, and im from norway, so my technical english is not that well... I wish to bias my amp to get it "healthy", but im not quite sure if i have understood how... well i guess i just have to have a go at it...

well, any digital multi meter will work, they aren't expensive. That place I linked you has bias probes and sell a seperate DMM, I know he ships international too. It's really easy to do, you just have to be very careful working around a live circuit. If you're not comfortable with live electrical circuits however, I would recommend having a tech do it. What parts didn't you understand in that video, maybe I can help.
"The fool doth think he is wise, but the wiseman knows himself to be a fool." - W.S.
amp clips
amp vids