Problem with my single rectifier, very very quiet

[Silvergun]

So i got home, was playing with my single rectifier, not even very loud and suddenly it cut out. I can still very faintly hear what i'm playing out of my cab, it's just extremely, very quiet. i was playing with it like that for a few minutes to see if something would happen, then it suddenly struggled up for power, staggeringly got louder back to normal. I though ok cool, it's fixed. played for about 30 seconds and it went down again. I tapped the power tubes and didnt hear any rattleing. Fuse is fine, amp-cab ohm is fine, guitar is fine.

Posted this on another forum, the main suggestion was to replace the power tubes, so i ordered a pair from doug and just put them in, still having the volume problem.
Anyone have a clue as to what is going on?

 

[Dale B.]

So i got home, was playing with my single rectifier, not even very loud and suddenly it cut out. I can still very faintly hear what i'm playing out of my cab, it's just extremely, very quiet. i was playing with it like that for a few minutes to see if something would happen, then it suddenly struggled up for power, staggeringly got louder back to normal. I though ok cool, it's fixed. played for about 30 seconds and it went down again. I tapped the power tubes and didnt hear any rattleing. Fuse is fine, amp-cab ohm is fine, guitar is fine.

Posted this on another forum, the main suggestion was to replace the power tubes, so i ordered a pair from doug and just put them in, still having the volume problem.
Anyone have a clue as to what is going on?

Like some of us suggested on HCAF, it could be the preamp tubes. V1 is bad about causing this. V5 (PI) is as well. If you use the effects loop, V4 could be the culprit. V3 could be bad as well, which would cause this.

If V2 went down, you would mostly notice a good bit of preamp saturation loss, but it could cause this as well.

 

[Silvergun]

How to i go about testing the preamp tubes? to i just take off the metal shielding with it on and give it a tap and listen for something? It happens on all channels, so i'm guessing maybe it is V1?

 

[Platypus]

Judging from an experience with my lonestar it sounds like a powertube went bunk and caused the screen resistor between the rectifiers and the power section to go bad.

When I called Mesa they said volume drops are usually caused by power tubes and not preamp tubes.

Try calling Mesa, they can walk you through a testing process to figure out what it is.

I could be completely wrong here, just giving my experience. Mine never 'came back' to a normal volume, just dropped for good.

 

[Dale B.]

Judging from an experience with my lonestar it sounds like a powertube went bunk and caused the screen resistor between the rectifiers and the power section to go bad.

When I called Mesa they said volume drops are usually caused by power tubes and not preamp tubes.

Try calling Mesa, they can walk you through a testing process to figure out what it is.

I could be completely wrong here, just giving my experience. Mine never 'came back' to a normal volume, just dropped for good.

Yes, a screen grid resistor can go if a power tube shorts, but amps will sometimes amp still operate if it has another power tube in it that is good. You will cut your power in half and you'll probably hear some massive hum in an amp that only operates on 2 power tubes. In amps that run 2 or 3 pairs of power tubes, some folks will never catch a bad screen grid resistor because they don't know how to check the negative screen grid voltage and cathode current on their amplifiers. Mesa doesn't help matters here.

If a screen grid resistor goes and you know how to solder, it's a pretty easy replacement if you know what you're looking at. Screen grid resistors cost anywhere between 50 cents and 2 dollars. You just have to have the right value.

Preamp tubes can cause the very same thing. V1/Input is very bad about causing this. The Phase Inverter (V5 in a Recto) can definitely cause this to happen as well. If the effects loop is active and there is a bad preamp tube in that spot, it can cause this as well.

The preamp feeds the power section. If there is something in the preamp not doing it's job, it will have a negative effect on the overall vibe of the amplifier.

As far as taking the preamp tubes out, push down on and rotate the metal anti-shock covers until they pop out. Then lightly rock the preamp tubes out of the sockets. The pin confiturations, when you put them back in, will be like an upside-down Omega sign or the opening will be up top.

Sometimes you can tell if a preamp tube has gone bad just by looking at it and sometimes you can't. If the getter exhaust has turned to white, instead of the dark silver, that means that the tube isn't sealed any longer. Also, if you notice any kind of gold discoloration inside the tube, it is bad. You would have to know what you're looking for here though.

Most tubes fail because the screen grid has shorted.


Dale

 

[Platypus]

Thanks for the clarification Dale

 

[Silvergun]

Thanks for the advice, i swapped V1 and V3, problem didnt fix, swapped V5 and V4, problem didnt fix, so i just ordered a new preamp tube from mesa (it better only be one busted tube...) I doubt they're open monday so i guess i'll give them a call tuesday. When i was playing it i heard some high pitched rattling, however i was having a difficult time figuring out where it was coming from.

 

[Silvergun]

Well got a new preamp tube today, swapped it in place of each tube and tested it, nothing changed Changed power tubes again, and again nothing :\ Guess i have to take it to a dealer/repair tech?
although after i put the old power tubes back in i could hear the fuzz i normally hear, then i hit a note, and a kinda loud pop occured and it went back to being quiet.