Power amp tubes

ggunn said:
Just to pick a nit, the axis of a speaker is a line out from the center of the dust cap perpendicular to the plane of the rim of the speaker. If your mic is between the dust cap and the edge of the speaker, it's not on axis.

There isn't a music store with an amp repair department where you live? I guess I'm spoiled; here in Austin there must be at least 20 of them.
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Just guitar center, but I wouldn't even trust those guys to breathe properly.
 
As a GC employee, I am feeling quite outnumbered here... but I don't work in the guitar department, so maybe that's some consolation. There are some amps that you can swap between different tubes (the Orange Rockerverb is one of them, as are several of the Mesas), so maybe he just didn't know your amp.

Check and see if your amp actually can be biased. There are a fair number of amps, including my Night Train, that are fixed bias, meaning that they just leave it at one setting that is designed to work with one type of tube. If you have a fixed bias amp, you can't change the bias, so you don't have to worry about it.
 
thebigcheese said:
As a GC employee, I am feeling quite outnumbered here... but I don't work in the guitar department, so maybe that's some consolation. There are some amps that you can swap between different tubes (the Orange Rockerverb is one of them, as are several of the Mesas), so maybe he just didn't know your amp.
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You are correct, but amps that allow tube swapping are the exception, not the rule. If he didn't know the amp, he should know enough not to make stuff up. If he was going to assume anything, he should have assumed that you could not swap tubes. Especially not EL34 to 6L6.

No one expects everyone at GC or any other store to know everything about all the products that are being sold there. That is a truely impossible task. What we do expect is a salesperson to admit that he isn't sure about something and look up the answer or ask someone who does know. Making assumptions and stating them as fact is a bad way of working. That is what has given the people at GC a bad reputation.
 
I'll go out on a limb: you *should* get the amp re-biased every time you switch power tubes. But... if you're replacing with the same model (e.g., EL34 -> EL34), you might get away without doing it. I have a JCM800 head that I got in the mid 80's - I've replaced the power tubes maybe 3 times and I've, um, never re-biased. I think the first swap may have even been from 6CA7 (which may have come stock? I had some loose ones and have no idea where I would have got them otherwise) to EL84. I was a teenager and not keeping track, and indeed had no idea what bias was.

The truth is that there will be a range of acceptable bias values, and unacceptable values on either side of that range that will result in crappy sound and probably greatly shortened tube life or other problems. The "good" range of bias values will be a little different when you switch tubes if the new tubes are a little different, and so if, with the previous tubes, your bias setting fell in the lower part of the good range, maybe it'll fall in the higher part of the good range with the replacements - sort of a crap shoot.

Also, it's worth noting that, inside the good bias range, changing the bias *does* change the sound of the amp a little, particularly with regard to break-up - so the amp tech who's setting your bias is using some judgment in coming up with the setting, unless you're sitting there with him/her and testing to come up with your optimal setting. That is to say, there's a chance that the interaction of the current bias setting on the amp with the new tubes will produce a sound that you like more. (and a chance you'll like it less, of course, and a chance you won't notice any difference with regard bias-affected sound attributes)

The point of this is that you probably don't need to worry about replacing say, the Ruby's with the JJ's, even though the descriptions on the website say they'll behave a little different. If, with the new tubes, the sound is really cold and lifeless (bad on the low side), or really farty and straining (bad on the high side), then maybe you have a bias problem and should go seek help (or put back in the old tubes). That hasn't happened to me with the Marshall, and I love the way it sounds.

now the disclaimer: I'm not an amp tech / electrician / EE, so take my opinion for what it's worth, and I also agree that the speakers and guitar/pickup/pickup height, etc. should be the first place you look to improve sound in the way you're describing.
 
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Farview said:
No one expects everyone at GC or any other store to know everything about all the products that are being sold there. That is a truely impossible task. What we do expect is a salesperson to admit that he isn't sure about something and look up the answer or ask someone who does know. Making assumptions and stating them as fact is a bad way of working. That is what has given the people at GC a bad reputation.
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I'm not saying he should be doling out bad advice like that, I'm just saying that's probably what he was thinking. Maybe he only tries to sell Mesas or something. I always look stuff up when I don't know or ask someone else. Our store is pretty good, but I can always feel bad vibes coming off people who are quite set on having a bad experience.

antichef said:
I'll go out on a limb: you *should* get the amp re-biased every time you switch power tubes. But... if you're replacing with the same model (e.g., EL34 -> EL34), you might get away without doing it.
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Kind of, but like I said before, there are some amps where you literally can't adjust the bias. Well, you can, but you have to swap out some resistors for potentiometers, which I did on my Blues Jr. when I still owned it.
 
You got some good advice here, but it seems like you just want to mess with the tubes anyhow.
Don't do it!
First you'll spend money on tubes, the re-biasing, then re-biasing again when you put the old tubes back (and you will:D)
A POS guitar and an MG cab IS the problem.
Better speakers will tighten up the bottom end and different guitars with different pups will polish it off for a great sound.
 
I have no idea what he is using, but that distortion really sounds like a stomp box run through a semi-clean amp. I could be wrong.
 
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