.50 Caliber + problem w/gutshot

[Metal_Mazzo]

Hi !

A few years ago, I bought this amp, and since then I got increasingly disaponted with its tone (not much gain, not much bass and either no definition or ear-piercing treble). Yesterday, I decided to open it up to see if there was anything wrong. I found an interesting (read "poorly done" ) mod to the circuit.

Are there any Caliber wizards in here that can tell me what was the modder trying to do, and how could it have affected the tone. Could the removal of whatever sat in that spot cause the unplesant qualities to the tone or should I look elsewhere.

The amp runs on 4 Fender labeled Groove Tubes 12AX7, an unknown 12XA7 in the remaining spot, and 2 Mesa 6L6 in the power section.


Sorry for the huge pics !

 

[SonicProvocateur]

Transformer lead wire (close to R26(?)) is burned and frayed.
Resistor R431(?, hard to tell from pics, maybe a shadow) looks burned up.

It's pretty close to the screen grid resistors, but those looks original and fine. I can't tell much about what those spragues are. Maybe monsta-tone can chime in...Is that 5W resistor coming off the big caps original? Mine were upgrades on my Mark III for more power handling...

 

[Metal_Mazzo]

So if I understand well, the problem lies in the power section, not the preamp.

I think I read somewhere that there is a mod to use the reverb circuit for more gain. Since the reverb ain't functionnal on the amp, I tought the guy who did the mod tried to do just that. But now, if he fiddled with the power amp, what the heck was he trying to do ?

 

[bigbean]

You have my condolences. That thing looks hacked.

Some serious overheating on the circuit board by r26. Was it desoldered by a moron or did the resistor overheat and scorch the board - easily enough heat there to lift a trace underneath. . The input jack what's going with that? That looks like it's been messed with by an "inexpert".

I think you need to "refer to qualified technician" who knows this vintage of mesa product with a mandate to return the unit to stock.

Seriously, I wish you the best with this.

 

[SonicProvocateur]

Looking again at pic #2, it's actually R261, not R26, but it looks like R261 was removed to put in that big blue cap as part of the mod for those 3 spragues.

Removing R261 and adding that huge cap seems to have caused the transformer to overheat your board for sure from causing too much juice to that part of the circuit (including the solder at R10P) and also fry the transformer lead; very bad. This could eventually cause amp/transformer death.

I would recommend PM'ing Monsta-Tone, as he is certified and can do de-mods and return it to stock, or at least fix the hack job and figure out whats wrong.

 

[Monsta-Tone]

Well, crap! My office computer is still down, so I don't have anything to cross reference too, but I'll take a shot anyway.....

The yellow capacitors are part of the Phase Inverter. Probably swapped to make the amp sound more Vintage or give it a different tonal feel.

The Resistor, R261 probably failed and burned the board due to some Reverb Mod.
Or, the guy tried to modify it and burned the board while de-soldering it.

I don't know why you have an extra Electrolytic Capacitor in there, sorry. Might be that this guy attempted the mod you are speaking of, but it looks like he tried to "Fix" the reverb instead.

Can't tell without looking at it in person.


Should take a decent tech a couple of hours at most to fix it.
I just moved back to Maui or I would offer. Shipping seems to be my worst enemy right now.

 

[Metal_Mazzo]

The yellow capacitors are part of the Phase Inverter. Probably swapped to make the amp sound more Vintage or give it a different tonal feel.

Well sir, I think you hit the nail right on the head with that. Everyone who tried the amp since I bought it commented how "rock " ( as opposed to metal ) the amp sounded. Would have made a great blues to hard rock amp, unfortunately, we're playing trash...

I guess I should take it to a tech. Does anybody knows if there is an authorised / certified Mesa tech, or at least a reliable amp repair shop, around Montréal ?

Thanks for your help guys, and if any of you has a picture of the internals of a healty 6L6 powered .50 Caliber, i'd be very curious to see it !

 

[Monsta-Tone]

Shoot me your email address. I have a few pics. They're not the best, but you will be able to see where the red wire goes, etc.

Also, have your tech replace the 2 PI capacitors with some .047 Orange Drop capacitors and the amp should have much more bite to it.

While he's in there, have him replace the 100 k ohm Carbon Composition Plate Resistors that are in the Preamp section. These create tons of hiss when they get old.
The amp will sound much more vital with Metal Film resistors.

Another thing that I really like to do is replace the Treble Capacitor in the Preamp section with a Silver Mica capacitor of the same value. This really makes the amp sound a bit more urgent and less Vintage.

 

[scottcrud]

Metal-Mazzo, listen to Monsta-Tone, he brought one of my .50Cal+'s back to life.