Mark IV acting up

[steeldragonjovi]

I was playing my rig yesterday and noticed the volume was dramatically decreased on my Mark IV when I turned it on. I figured someone had just turned the volume down, but when I turned it up, it wasn't loud. I flipped it off, tried it again, but same problem. When the amp is on, the tubes glow purple, but they glow slightly orange in standby. Also, it pops and crackles every so often and has been doing that for a while.

Any tips for diagnosing the problem? I'm assuming it's a tube problem, but is there a way to isolate which tube it is? Perhaps, changing the power options so it only runs two tubes at a time and switching them in and out to find it?

 

[Triaxstasy]

Sounds like (a) faulty tube(s)....
Slightly knock/tap on each tube (preamp-, pi- and powertubes) with the handle of a screwdriver....should be easy to find out which one(s) is the bad guy.
Could be either the PI or the powertubes....

 

[steeldragonjovi]

Okay, so just do that while everything's on?

Also, is the PI the power input? How do you hit that one?

Sounds like (a) faulty tube(s)....
Slightly knock/tap on each tube (preamp-, pi- and powertubes) with the handle of a screwdriver....should be easy to find out which one(s) is the bad guy.
Could be either the PI or the powertubes....

 

[Triaxstasy]

PI = Phase Inverter (tube)...that´s a 12AX7

Turn the amp on and let it warm up.....then knock/tap on each tube, one after the other.....you should "hear" the bad one(s)

 

[steeldragonjovi]

Okay, thanks. I'll give it a shot.

 

[Triaxstasy]

Okay, thanks. I'll give it a shot.

...a slight tap is sufficient!! 8) 8) 8)

 

[topcat0399]

Okay, thanks. I'll give it a shot.

...a slight tap is sufficient!! 8) 8) 8)

a pencil is a better hammer than a screwdriver for this task.....

 

[steeldragonjovi]

Okay, I went through and tapped the power tubes and the preamp tubes, and I didn't get anything. I made sure the amp was on and warmed up, but the only sound coming out was the usual popping and stuff.

Any ideas?

 

[bgh]

Do the same symptoms occur when you switch to class A mode? If so, that would quickly eliminate two tubes.

Mine was generating a fluffy sort of sound when it was in simul-class mode. It went away when I switched to class A. I replaced the inner pair of 6L6s and the trouble went away.

 

[steeldragonjovi]

I tried switching the to Class A, but it still made the same noises. However, when I went from full power to tweed power, it stopped. Any ideas?

 

[Triaxstasy]

I had that same behavior with my 50/50 some moons ago....Crackling noise in Hi-Pwr, everything fine in Lo-Pwr....turned out that it was one resistor in the bias circuit. replaced all components in the bias cicrcuit (2 caps, 4 resistors) and everything was fine.

 

[steeldragonjovi]

Did you do that yourself or have to take it in to a shop?

I had that same behavior with my 50/50 some moons ago....Crackling noise in Hi-Pwr, everything fine in Lo-Pwr....turned out that it was one resistor in the bias circuit. replaced all components in the bias cicrcuit (2 caps, 4 resistors) and everything was fine.

 

[Triaxstasy]

I did that myself....but leave it to a pro tech if you´re not too handy with a soldering iron and the stuff and - most of all - the lethal voltages that goes on inside a tube amp.

 

[BlackBoxy]

I was playing my rig yesterday and noticed the volume was dramatically decreased on my Mark IV when I turned it on. I figured someone had just turned the volume down, but when I turned it up, it wasn't loud. I flipped it off, tried it again, but same problem. When the amp is on, the tubes glow purple, but they glow slightly orange in standby. Also, it pops and crackles every so often and has been doing that for a while.

Any tips for diagnosing the problem? I'm assuming it's a tube problem, but is there a way to isolate which tube it is? Perhaps, changing the power options so it only runs two tubes at a time and switching them in and out to find it?

seems your 6l6 line is dead , purple and bright orange are the pre stage to burn the trany, change PI if you replace power tubes