Mark V:25 Gain Drop on CH2

[HK Expat]

I was experimenting with a new overdrive pedal this past weekend, that being the AnalogMan King of Tone. Had an interesting phenomena happen on the Mark V:25. At one point the gain suddenly dropped substantially on CH2. I checked all of the settings and they were OK – both channels on 10W and both channels had EQ on. Nothing significant had changed in the settings, but I suddenly lost volume on CH2.

Previously I would set the Gain and Master volumes on CH1 and CH2 to similar settings, but now I need to turn up the m CH2 master to 9:30 to get roughly the same volume that I get on CH1 with the master at 7:30 or less. CH2 is not noisier than before, nor does it have any other obvious problem other than the sudden drop in loudness. When I turn it up to compensate for the volume drop, it still sounds good.

I looked at the tube diagram in the manual and noted that V2B is the 4th gain stage for CH2 and V2B is not used for CH1, so I suspect V2 may need replacement. Funny thing is that I had a very similar problem on my TA-15, and changing the correct preamp tube fixed it. However, I believe that the tubes are quite difficult to access in the Mark V:25 and the grill cloth can be difficult to assemble back into the cabinet when you are done. So I before I start to take it apart I would like to hear some feedback here.

By the way, I noticed that the manual does not mention which tube section is responsible for the CH2 3rd gain stage. Funny that they wouldn’t mention this in the manual.

 

[Dreamtheaterrules]

I don't know what you mean by "sudden drop" in volume, but my C2 has to be much higher on the master than C1 does to match volumes. With C1 on fat, gain at noon, the volume at 9:00 is almost too loud for home. I play at 8:00-8:30. C2 rides at 10:00 or higher to match the volumes. I've played at least 3 others in the store and they were all exactly the same way.

 

[Rectifried]

I don't know what you mean by "sudden drop" in volume, but my C2 has to be much higher on the master than C1 does to match volumes. With C1 on fat, gain at noon, the volume at 9:00 is almost too loud for home. I play at 8:00-8:30. C2 rides at 10:00 or higher to match the volumes. I've played at least 3 others in the store and they were all exactly the same way.

Yes mine is like this as well.

 

[HK Expat]

Thanks Dreamtheaterrules and Rectifried for your helpful insights. Maybe this is all perceptual on my part. I was sure at the time that I had a sudden loss of gain, but your comments as based on several different samplings of Mark V:25 amps is useful.

The only other difference that I have noted is that previously I would get a fairly loud "pop" when I channel switched from CH1 to CH2. That no longer happens, so I still have a hunch that something has changed.

 

[Dreamtheaterrules]

I think you're good to go. When I get a new amp, pedal, etc. I always give all the switches a few flips and roll the knobs around. Switches especially can sometimes need a few cycles to work properly. I've had several amps and pedals that were purchased new that had switches that were a bit finicky at first. Flipping them thru their range a few times seemed to fix it and no problems since.

Good luck with the amp!

 

[jmontgomery]

V1 is about impossible to get to but if you have deft fingers you can get the rest without pulling the chassis. That said, pulling the chassis makes it easy.