changing tubes

K7 · #1 03-20-2003, 10:15 AM

hi guys!
today my new (and first

) tube amp has arrived. it's a marshall jcm 800 50w head from 1983. what tubes would you recommend for it? what is the difference between ecc83 and 12ax7 preamp-tubes and between el34 and 6550 poweramp-tubes?
thanks, alex

EKG · #2 03-20-2003, 11:02 AM

Go to www.eurotubes.com. I recommend the JJ tubes. The ecc's supply more gain and the el34's have the classic Marshall sound.

microdmitry · #3 03-20-2003, 01:55 PM

There's NO difference between ecc83 and 12ax7. ECC83 is a European name of this tube. 6550 is also known as KT88 and it's got almost twice as much power as EL34. If you're thinking about replacing EL34 with 6550, make sure you know what you're doing. You can fry your amp. 12ax7 and ecc83 are interchangeable (obviously) without any problems.

mike777 · #4 03-20-2003, 02:16 PM

Just remember that unlike strings, you don't just change them. The amp should be re-biased to operate properly. I've never done that myself but I hear that it's very easy, sort of. From what I've been told, most newer amps require an oscilliscope(sp) for this. Not sure about a Marshall from '83, though.

Mike 777 Haug

microdmitry · #5 03-20-2003, 10:37 PM

That's not correct again. First thing is, not every amp needs rebiasing after a tube change. UniValve for example doesn't. Majority of them do. Another thing is that re-biasing never requires an oscilloscope. $20 multimeter will serve the purpose just as well. Having said that, I must mention that tube amps use LETHAL voltages. If you don't want to die and you're not sure about your skills, refer servicing your amp to a qualified technician.