I have a line 6 spider valve 112 and after I play for about a minute it starts emiting a loud screeching noise and I just turn the amp off. Im not sure which tubes are causing this problem. As well Im not sure how to change the the power amp tubes or the pre amp tubes (I dont know where the pre amp tubes even are) as well the power amp tubes are enclosed and im not sure how to open up the enclosure to get to them. Any Ideas?
welp ive got the same amp so...

you cant find the preamp tubes becuase its a hybrid amp, its got a tube power amp and a solid state preamp.

i havent had to change my tubes yet but i assume after you get the cover off the tubes they come out and go in just like any other tube amp.

and to check if the tube is bad leave the amp on for 5-10 min and watch the tubes while your flipping the standby switch, if 1 tubes bad it wont light up a blue purple color
How Do I check the pre amps?

I just check amp both the power amp tubes appear to be fine
Last edited by 123mac123 at Jun 5, 2010,
Quote by 123mac123
How Do I check the pre amps?

you dont need to it doesnt have tubes.
The spider valve does have a tube gain stage at the input, the other preamp tube is the phase inverter.
But anyway, getting to the power tubes shouldn't be aproblem if you have a screwdriver, try to find the screws that will allow you to remove the enclosure.
As for the preamp tubes, if you can't see them, they most likely are inside the chassis.
Ya I found the pre amps they are behind the the power tubes, though visually I can only see one, but I know they are both there. Still since Im going to go buy a couple tubes how Can I test the pre amps, though generally I think the loud screeching noise wouildnt come from the power amp tubes, and they appear to look fine