This may be a stupid question, but I heard a bang & my power cut in half, it was shortly after turning it back on to 'play' after swapping a module. I had a tube failure light on and found that the fuse has blown. Replaced it and it all works fine. If the power tube in question still bias's the same as before, do I have nothing to be worried about?
Power tube question
- Thread starter RADE01
- Start date
Help Support Synergy/MTS Forum:
Ampoholic
Well-known member
So the same power tube is in there? I would replace it. It may not be necessary, but why take chances. Everytime time those circuits pop, I believe there's a chance of greater damage.
Yeah same power tube. It still lights up just like all the others. What damage could it do if that tube is not good enough anymore?
What are the tube failure lights for if they don't tell you when there's a problem with the tubes?
What are the tube failure lights for if they don't tell you when there's a problem with the tubes?
JKMV12
Well-known member
well it sounds to me like the tube started red plating. this happens when the tube starts to draw too much current. the fuse is there to make sure the tube doesn't stay this way for too long. if it does then you risk frying another part of the circuit. the light should come on whenever the fuse is blown. it may look fine now but if can happen again and if it does you risk causing serious damage to the rest of the amp...which will result in a much larger repair bill than just getting a new tube. so to be on the safe side just replace the tube.RADE01 said:
Ok then, I do have EL34B-STR's in there at the moment. I can put my 6L6's back in.
I seriously only got it back from repair about 3wks ago! :? Had the screen grid resistors and one of the power tubes replaced.
I never abuse the amp or run the bias hot, so I would hope not to have any trouble for a while.
Thanks for the advice.
I seriously only got it back from repair about 3wks ago! :? Had the screen grid resistors and one of the power tubes replaced.
I never abuse the amp or run the bias hot, so I would hope not to have any trouble for a while.
Thanks for the advice.
Tbag
Well-known member
i have used the EL34B STR's, and found them too dark and when cranked they would compress and lose top end at gigging volumes.
The best EL34's are the Tung-Sol EL34B's dude! seriously.
But as Gerald Weber says, 99% of the time when that fuse blows, it's a power tube gone/going bad, so replace them no matter what.
You say "one" of the power tubes were replaced? That can't be a clever move by your amp tech :S Unless he is unbelievably 200 million thousand % positive it was matched to the other 3 power tubes lol
Are you sure it biased up ok again? You need to measure 'across' the tubes to read the difference in tolerance they have.
The best EL34's are the Tung-Sol EL34B's dude! seriously.
But as Gerald Weber says, 99% of the time when that fuse blows, it's a power tube gone/going bad, so replace them no matter what.
You say "one" of the power tubes were replaced? That can't be a clever move by your amp tech :S Unless he is unbelievably 200 million thousand % positive it was matched to the other 3 power tubes lol
Are you sure it biased up ok again? You need to measure 'across' the tubes to read the difference in tolerance they have.
Julia
Well-known member
It doesn't matter. I had two tubes in a quad fail right out of the box. Installed. Then bang with a lightning flash (tubes arced) and both fuses blew. Bad tubes tend to come in lots. Just toss the bad tube, then pull the others in the quad and replace them. Keep the ones that didn't fail as spares. Chances are they will probably fail early on.
If tubes are bad they usually will fail within the first month. It doesn't matter how loud or whatever you play. That's the reason that 99% of other applications moved away from tubes years ago.
If tubes are bad they usually will fail within the first month. It doesn't matter how loud or whatever you play. That's the reason that 99% of other applications moved away from tubes years ago.
The amp repairer went to great lengths to find a JJ6l6GC tube that would match the rest of the quad.
The TAD EL34B-STR's are some I bought a couple years ago that I put in after I got it back, and yes Julia, they have had less than a months total use. I put my JJ6l6's back in lastnight, I do also have a fairly new quad of Ruby's and also a pair of TAD 6l6GC-STR that I used prior to the repairs. I thought they sounded pretty good.
How about KT66's? I have a pair of them that I could stick on the outside if anyone thinks they're good?
Also, if your bias is too low it won't damage anything will it? I mean, I've had a 5150 ll since 2003 and never had an issue. They're pretty cold.
Thanks for the help folks.
The TAD EL34B-STR's are some I bought a couple years ago that I put in after I got it back, and yes Julia, they have had less than a months total use. I put my JJ6l6's back in lastnight, I do also have a fairly new quad of Ruby's and also a pair of TAD 6l6GC-STR that I used prior to the repairs. I thought they sounded pretty good.
How about KT66's? I have a pair of them that I could stick on the outside if anyone thinks they're good?
Also, if your bias is too low it won't damage anything will it? I mean, I've had a 5150 ll since 2003 and never had an issue. They're pretty cold.
Thanks for the help folks.
Julia
Well-known member
Matched tubes are a pretty recent thing. They didn't used to have matched stuff until the Interwebz. Now I've seen "matched" preamp tubes.
My amp tech was trying to find a JJ6L6GC that had similar or the same measurements as the others, or atleast the other outer tube. What those measurements are I don't know. I assume resistance and stuff with a multimeter.Julia said:
"Matched" preamp tubes, is that a joke or what? I rarely use the same ones together anyway. :lol:
JKMV12
Well-known member
i believe the reason for matching power tubes is that when using a push pull power amp the tubes are meant to work equal and opposite to each other. if one set of tubes was working harder than the other (i.e. drawing more current) then the effects could be detrimental to the output. though i could be wrong on that...RADE01 said:
Now in case there is any confusion...preamp tube matching is NOT two separate tubes being matched. It is making sure that the two triodes inside each tube are matched (i.e. have near identical characteristics). Now i have heard that his can be useful in some applications such as the phase inverter. Matching two separate preamp tubes would be ridiculous. Though making sure the triodes inside match...it may be an attractive concept to some people.
Tbag
Well-known member
i always use balanced phase inverter tubes 
kc2eeb
Well-known member
I wouldn't even worry too much about balanced PI tubes.
The PI in the MTS series follow the "long tail" PI layout so the
one swing of the wave is througt an 82K resistor and the other
is through a 100k resistor, in typical "Fenderish" fashion.
Just trust your ears.
The PI in the MTS series follow the "long tail" PI layout so the
one swing of the wave is througt an 82K resistor and the other
is through a 100k resistor, in typical "Fenderish" fashion.
Just trust your ears.
Julia
Well-known member
I just stick whatever tube I have handy for the PI so long as its low noise.
But on the power tubes, the bias will drift around for about a month or so with use until they get a good burn in.
Speaking of guitar. I need to start playing more again. I've been focusing on keyboard work and coming up with some decent stuff. I'll tell you playing 3 instruments takes time. (keyboards, voice, guitar).
But on the power tubes, the bias will drift around for about a month or so with use until they get a good burn in.
Speaking of guitar. I need to start playing more again. I've been focusing on keyboard work and coming up with some decent stuff. I'll tell you playing 3 instruments takes time. (keyboards, voice, guitar).
