Strange 5150 problem

[MetalSound]

My 5150 lacks power and bass. I can boost it up to 10 and it just gets muddy. I once played it at another cabinet and suddenly it was 10 times louder! All tubes are new and the impedance switch was set up correctly.
When I crank it up to 8-9 the power tubes are lighting differently and the bass "swells" up and down. Any ideas what might be defect?!
By the way, it has the same power and loudness when I take out two power tubes (no matter which ones...) but they are all shining fine blue and red.

 

[VH100R]

the swell is generally a tube issue.

if you have all the gain in the channels but really low volume thats a PI tube issue.

usually its the last of the preamp tubes. it happened to me twice.

Just swap the last tube with another preamp tube.

hope it helps.

take care

LG

 

[MetalSound]

Thanks for the tip but that didn´t help.
What is PI?

 

[greyskull]

phase inverter

 

[JeffTD]

Sounds like shit powertubes to me.

My tubes don't shine blue .

 

[kaomao]

there's no problem if it's shining blue, it's just the gas inside the tube that creates that colour.
not always you can find tubes vacuum-packed, it should be a standard though.

 

[Erik Monsonis]

Tubes don't have to shine blue. In that case they are fucked up

 

[MetalSound]

No, the tubes are alright. I tested them in another amp and they worked fine.
Even changing the power tubes didn´t change anything....

 

[kaomao]

Tubes don't have to shine blue. In that case they are fucked up

Well it's a common thing that people claim their tubes shine blue, so I have to think there's a huge amount of fucked up tubes?
I read on the internet that blue shining is just gas that remains inside the tube wich reacts with oxygen.
My dual rectifier sounds good as my peavey 5150, and they got that kind of glowing going on.

 

[Wolfeman]

Well it's a common thing that people claim their tubes shine blue, so I have to think there's a huge amount of fucked up tubes?
I read on the internet that blue shining is just gas that remains inside the tube wich reacts with oxygen.
My dual rectifier sounds good as my peavey 5150, and they got that kind of glowing going on.

You are right, the blue is just gases left inside that didn't fully get sucked out under vacuum. Don't worry about that, alot of my tubes do that, some more so than others. In fact my SED winged C's are extremely blue, and look/sound awesome

 

[ryanojohn]

I would assume you've got faulty wiring either in your cabinet, or in your impedance switch... Faults in the switch would be pretty hard to do, so check the cab first... open it up, check for faults in the wiring, a loose wire, a wire touching another where it's not supposed to... some (weird) cabs have fuses to protect speakers from overload... check that none have blown (if they had it SHOULDN'T be making sound from that speaker... but hell weirder things have been known to happen), try unplugging two of the speakers, and running only two of them, be sure to check if they're in parallel, or series and set the impedance to match their arrangement. If the situation improves at all, you can assume one of the speakers is dead, and maybe a voice coil has burned out and is causing a short...

It doesn't sound like an amp head problem... especially since another cab performed at 'ten times' the volume... with the impedance correctly setup, unless those were lower wattage speakers...

 

[MetalSound]

No, the cab is definetely okay. It´s a Mesa Std. Recto and it runs on 8 ohms. I´ll check the amp switch but I played the 5150 at a 16 ohm Marshall and there was no difference (the impedance switch was set to 16 ohm accordingly of course).
When I played it with another Marshall cab it suddenly was much louder....when I returned it to my Mesa afterwards it was one day loud and the next day I played it is was as low in volume as before.
Any other ideas?

 

[Loren Littlejohn]

What speakers are in the recto cab?

What speakers or what cab was the louder cab?

When is the last time a qualified tech looked at your amp?

 

[MetalSound]

In the MESA there are the standard factory V30s (no changes).
I play the amp in our rehearsal room with a Marshall Lead 1960 and at the gig where the amp was suddenly louder it was a Marshall 1960 with Greenbacks.
I bought the amp used so I suppose there has been something wrong with it before.....

 

[Loren Littlejohn]

How long have you had the cab?

 

[MetalSound]

For half a year now, it is black and it is in fully working order.

Edit:
AAAAARGGGGHHH, there is the power and bass again after a transport to our rehearsal room and playing it with the Marshall Lead 1960. In the beginning it was as powerless as before but after switching it off and then after a short time on again.....there was the loudness and bass.
It didn´t matter if I played it at 4 ohm, 8 ohm (2x12") or 16 ohm. It had the full power.....HELP ME PLEASE!!!!

 

[MetalSound]

any ideas before I search for a technician?

 

[GuitarMaestro]

Try two things:

1. Run a cable from the FX SEND to the FX RETURN and then test the amp with FX loop switched on and off. I dont remeber exactly why, but dirty/old jacks or the switching relay for the FX loop are often causing problems like yours with the 5150, even if you dont use the FX loop and closing it that way avoids the problem.

2. Listen to the preamp out or FX send with your DAW or something and check if the problem is in the preamp stage. If not record the power amp out with a speaker simulator and check if the problem is in the power amp. That should help you to find where the problem is....

In reference to you original post: Most people think that taking out two power tubes from a tube amp with 4 tubes makes a notable difference in volume. In reality the difference is nearly not audible, because to double the volume you have to have 10 times the power. For example: a 100 Watt amp is only twice as loud as a 10 Watt amp.

 

[MetalSound]

Hey GuitarMaestro thanks for the tip. The FX send/return seems to be the problem. At the moment it´s completely functioning.

You guys rock!

 

[GuitarMaestro]

Glad that I could help. You could ask jerry at http://www.fjamods.com. I guess he can tell you how to fix the problem yourself. IRC he gave me the tip with the FX loop, but as I said I dont remeber exactly why that happens. It should be an easy fix though.