Problem with Mark IV

Ronnie_Rocker · Apr 16, 2006

hi all! this is my first post here. I own a Mesa Boogie Mark IV medium head from ´90-´91. I changed the powertubes recently with Mesa STR 430. my problem is that after about 5-10 minutes of playing, the trible gets dull. i tryed to switch on-off on the stand by a couple of times, and each time i did that the trible got better, but just for a few seconds, the got dull again. i tryed to change the poweramp setting to Class A and triod. the same results accured. is this a poweramp problem, or is it the preamp? i havn´t changed the preamp tubes for a long time thou.

any ideas?

regards!

/Ronnie

Boogiebabies · Apr 16, 2006

Try new preamp tubes first. It may be coincidnece that this happened when you changed power tubes. Mainly I would be concerned with the V1. This is where the MK IV see the guitar signal and then sends it directly to the EQ.

Ronnie_Rocker · Apr 16, 2006

Boogiebabies said:
Try new preamp tubes first. It may be coincidnece that this happened when you changed power tubes. Mainly I would be concerned with the V1. This is where the MK IV see the guitar signal and then sends it directly to the EQ.

ok! im going to buy some new preamp tubes when i get cash. if it doesn´t help, i´ll need to get it to service!

Boogiebabies · Apr 16, 2006

Try swapping the 5th preamp tube for the first. The PI is usually punished less than the V1 and you may be able to diagnose it to one tube and save some cah for now.

Ronnie_Rocker · Apr 16, 2006

Boogiebabies said:
Try swapping the 5th preamp tube for the first. The PI is usually punished less than the V1 and you may be able to diagnose it to one tube and save some cah for now.

yeah. done that, but its the same problem. i belive that all my preamp tubes are old and need to be replaced any ways. i have the old version with four 12AX7 and one 12AT7.