Mesa 50/50 Power amp Problems

[RICKJG27]

Hey, new to the board. Signed up cause i need some help with my mesa boogie 50/50.

My set up is as follows
Mesa 50/50 Poweramp (second hand, early ninties model)
Rocktron Prophecy Preamp- Midi Foot controller
Wah
Guitar

Been having problems with my sound, really bad hum coming from the 50/50 (out the speakers of my 4x12) especially when the volume is turned up.
The Volume and tone seem to dip in and out making it sound very weedy, sometimes when i disconnect the midi controller from the preamp and put them back in the volume and tone come back to life.
Brand new power amp tubes have been put in it, but this has not changed the problems, plus for about the last 6months or more the blue light (my model has the blue cut glass cover) keeps fading in and out of brightness, and after practicing for a while it sometimes goes out completely. Is this to indicate any problems??

Im getting really bad feed back and what seems to be earthing problems when my guitar volume is turned down i have to touch the guitar to stop the noise, the guitar has been fitted with brand new dimebucker and 59 seymours with new 500k pots? it was doing this before refit

Im beyond confused as to whats going on, could anybody shed some light on the above.
Also, I havent changed the preamp tubes yet could that help?

Thanks, and sorry for the long winded questions.

Rick
NIreland

 

[RICKJG27]

Any help would be great thanks

 

[disassembled]

Do you have another guitar and cable to try? The problems you are having don't sound like the power amp is at fault because the noise is not there when you turn the volume down. Maybe your gain is too high and you are too close to the speaker?


Greg

 

[zeeman]

The problems you are having don't sound like the power amp is at fault...

Are you sure? He did say...

...plus for about the last 6months or more the blue light (my model has the blue cut glass cover) keeps fading in and out of brightness, and after practicing for a while it sometimes goes out completely. Is this to indicate any problems??

That does not seem like normal operation to me.

Rick,

No, the blue light fading in and out or going out completely is not to indicate problems. The only purpose for the blue light is to indicate that the power amp is on.

However, it should not be fading in/out or going out completely.

There is something wrong with you amp.

My suggestion would be to take it to a qualified Mesa repair center and have them take a look at it.

Hope this helps.

zeeman

 

[disassembled]

Ok, so install a new lamp and see if that fixes the light. IIRC the light is 120 volts so it is supplied by the AC outlet power and not the transformer. IMO worrying about a bad light is a waste of time until you fix the audio problems. A flickering light doesn't indicate anything other than a bad light or bad electricity.


Greg

 

[disassembled]

There seem to be several issues here and until you get them individually sorted out it is impossible to troubleshoot.

Take the power amp to a shop and as to try a preamp with their cables and cabs.


Greg

 

[RICKJG27]

Thanks for the response,

Yeah im going to get it checked by a tech hopefully. The light problem may well just be a dodgy light bulb, but it is strange, surely if it was a problem with the bulb it would just not work??
As for the hum, it is there when the volume is turned to zero and worse when turned up. I switched the pre amp off and it is still doing it, so its defo a fault with the power amp. Plus the amount of output ranging from massive to very weedy sounding, to me indicates there is something wrong with the poweramp.
Plus tried it with other cables etc no resolve.

Thanks again

Rick

 

[disassembled]

I had the 50/50 and from what I remember it wasn't the most quiet poweramp Mesa Makes (the 2:90 and 20/20 were almost dead silent in comparison). I will say that if you have a bad ground the amp will make noise or if the ground switch on the back of the amp is set improperly it will hum.

The light bulb can flicker as it dies but it isn't indicative of a problem that relates to what you're reporting unless the two problems are coinciding (IE the amp hums and feedsback only when the light goes dim).

Another thing you haven't mentioned are the 3 preamp tubes inside the power amp. Before you take it to a tech I recommend lifting the cover and turning the amp on with all three preamp tubes removed. If the amp STILL makes noise and hums then the problem is definitely going to require a tech. The amp SHOULD be silent with the preamp tubes removed. I would then add the preamp tubes one by one starting with the one closest to the fan and on down. The preamp tubes closest to the fan are the phase inverters (used directly for the power tubes) and the one closest to the input jacks is the input tube. If you have 3 spare preamp tubes that would be an even quieker way to troubleshoot as long as you know that the spares are in good working order.

BTW running an amp without preamp tubes won't hurt it.


Greg

 

[RICKJG27]

No the noise is always there no matter if the light is on or off. my friend has more recent but still second hand 50/50 and his does make some noise, but not to the extent of mine.

Yes i must try the pre amp valves. i dont have spares though. By taking them out and putting them in one by one, you do mean while the amp is switched on or off?? dont want a nasty shock lol.
The ground switch is set to normal, even though it is in a rack case, the lifted position is even worse for noise!!

Will let you know if the pre-amp valves make any difference.

Thanks again for all your help
rick

 

[disassembled]

Definitely power off and have the amp UNPLUGGED while sticking your hands inside changing tubes.

Be sure to remove any neck chains, rings, bracelets, watches, etc before moving your hand near the inside of the amp.


Greg

 

[astro929]

my light has never worked bought it 2nd hand, what bulb would i need and is it just plug and play