strange thing happened to my mark IV tonight:freaked me out

I was just jamming out a little on it and all of a sudden all of the gain disappeared from the lead channel.
I still had my volume but it was completely clean.
I switched over to R1.....fine
R2.................fine
back to lead.........still clean.
I turned it off and went upstairs. came back down 10 minutes later turned it on and it was working fine again,
but the lead channel sounded a little "thin".
I looked at the tubes all seemed ok, I schecked them all to make sure they were all seated properly.........OK.
any idea what's going on here?

Does the Mark IV use ldr's to change channels? Maybe it's a bleeding or dead LDR.

scott

You might want to first quickly check the preamp tubes. I had the same thing happen to my IV, loss of gain and distortion on the lead channel, but R1 and R2 were fine. Found a preamp tube that looked fine but must have been slowly failing and replaced it. Sounds great now. Good luck.

+1 on checking tubes. Tubes should be the first place to check out...
Scott

ok thanks guys I will do that tonight wehn I get home from work, any idea which tube is 'assigned" to the lead channel (if there is one)?
I noticed when I looked into the back of it last night that 2 of the preamp tubes have sleeves on them
is there a tube layout for the IV "A" anywhere?

kmanick said:

ok thanks guys I will do that tonight wehn I get home from work, any idea which tube is 'assigned" to the lead channel (if there is one)?
I noticed when I looked into the back of it last night that 2 of the preamp tubes have sleeves on them
is there a tube layout for the IV "A" anywhere?

Click to expand...

V3(first lead stage) & V4 (second lead stage) preamp slots.

Manual (page 21): http://www.mesaboogie.com/manuals/Mark 4.pdf
~Nep~

muchos Gracias!

Neptical said:

kmanick said:

ok thanks guys I will do that tonight wehn I get home from work, any idea which tube is 'assigned" to the lead channel (if there is one)?
I noticed when I looked into the back of it last night that 2 of the preamp tubes have sleeves on them
is there a tube layout for the IV "A" anywhere?

Click to expand...

V3(first lead stage) & V4 (second lead stage) preamp slots.

Manual (page 21): http://www.mesaboogie.com/manuals/Mark 4.pdf
~Nep~

Click to expand...

^it's 'muchas gracias' :wink: