LSC no longer sounds warm

[gregrjones]

My LSC is no longer sounding warm to my ears.

I looked around back to see if something was wrong with the tubes and I did notice that the rectifer tube was cold and not lit even when I switched the amp to Rectifer Tracking and kicked in 100 watt mode.

It also seems like the rest of the power tubes are running cold. They light up but after playing for about 15 minutes, I noticed that I could touch them without burning my hand.

What could be the problem?

 

[Vogelsong]

I'll be watching this one closely.

Another thread thats gonna teach me something. I love this place.

 

[ziehmrd]

As far as the rectifier tube, it is not used in the 100 watt mode, only in 10/50 watts when rectifier tracking is selected. As for the other tubes running cold, I'll have to check mine to compare but I know when I have the fan running, they never get too hot.

 

[Chester]

Power tubes are the normal culprit if the amp is starting to sound "brittle" - depends on age, and how much play time they have had. All it needs is one in the link to fade

Try swapping their positions if you play lower power settings - move inners to outer position, and see what happens. If you play at 100 w most of the time, try a total swap

Could also be the preamp tubes - V1 and 2 are the more important ones. I have a bunch of them and swap out depending on what I want to achieve. I recently swapped EH 12AX7's to crunch / grain up the amp a bit more, take out some mid range smoooooth and get better balance for what I wanted the LSC to do

Trial and error in valve amps is the norm - so have some fun finding your sound!

 

[gregrjones]

I'll switch the amp back to 50 watts. I was mixed up on how the power tube tracking works.

However I doubt that rectifier tube will change its behavior because when I first noticed this problem, I HAD been running in 50 watt mode.

You think this is a tube issue over a bias issue? I was wondering if the amp might need rebiased (perhaps it is running cold).

 

[plan-x]

Brrrr, I hate cold tubes. I heard tubes can get that way as they get older. The bias mod would definitely be a ble to warm things up. Also, not to be overlooked, the ears get accustomed to sounds, and are looking for a new high.

 

[djw]

This happened with my amp recently too. Some new power tubes warmed it right back up.

Not sure about this, but my understanding is that preamp tubes last a lot longer than power tubes. Can anyone corroborate this?

 

[gregrjones]

Update: I discovered that my amp now want even play in 50 watt mode. I only get a signal in 100 watt mode.

Does that mean that one or two tubes are out (whatever pair is engaged when in 50 watt mode)? If so, does the inner or outer pair affect 50 watt mode?

If I swap the pairs and keep the amp in 50 watt mode until getting new tubes, could that damage the amp?

 

[djw]

Probably means your rectifier tube is out. I'm pretty sure if one of your power tubes was dead you'd hear really bad things for a few seconds, before your fuse blew.

 

[Vogelsong]

+1 on the rectifier.

 

[gregrjones]

I swapped the tube pair and still got the same symptoms: Amp is dead on 50 watt mode and gives me a colder signal at the 100 watt level.

If the Rectifier tube is out, then shouldn't I still get a normal tone when switching to diode for both wattage settings"?

 

[gregrjones]

Ahhhh.... I just tested it and you guys are right. It must be the rectifier tube because the amp acts normally in diode mode.

However, the tone doesn't sound as warm to me. Does that part make sense?

 

[djw]

Your power tubes could still be getting on the old side. A separate issue. If you can, also try your amp in different environments, sometimes irregularities in the AC circuit can make your amp sound funny.

 

[Don]

Replace the PI tube as well. It's a hard working tube and a bad one will cause a lot of problems.

 

[PilotSSW]

+1 on the phase inverter, this tube makes alot of difference in the lonestars; at least it has for me. These not only affect your overall tone, so if the tube is dark both channels will be dark (or vice versa) but they also drive your power section (if they aren't balanced -- as well as if the power section isn't too) then the tone suffers and the power section/phase inverter works harder.
Hopefully someone can confirm this for me, but I believe when in rectifier mode, the rectifier also supplies power to the preamp tubes as well ? Is that true ? If it is, it would be all the more reason to go ahead and replace it as well.

P.S. mesa's stock tubes run very cold in my lonestar, I could touch any tube without much discomfort. However, when I put JJ's KT-77's in there it was a whole new story, you could feel the heat radiating around the room.