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Old 11-12-2012, 04:14 PM   #1
Unholy.Daemon
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Tube and Biasing Question

Hey all

I recently bought 2 new JJ E34L's for my amp, and I just wanted to know whether it's safe to put them in without biasing the amp.

I've been searching around and most people seem to say it's generally ok, but switch the amp off as soon as you get any signs of redplating. I also saw a suggestion to put the bias adjust right down to 0, the coldest setting and then move it up until it sounds right and isn't too hot; is that ok to do?

I just wanted to test this out to see if replacing the tubes will fix the popping noises my amp was making because I don't have a mulitmeter to be able to properly bias my amp, so I'd appreciate any help.

Thanks!
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Old 11-12-2012, 04:15 PM   #2
R45VT
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What amp??? The one in your sig?
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Old 11-12-2012, 04:23 PM   #3
Unholy.Daemon
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Yeah, Randall RH50T
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Old 11-12-2012, 04:33 PM   #4
R45VT
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I didn't find crap on it. Manual is a cheap photo copy even on Randals site.

Are there any Bias points in the back of the amp? Have you ever opened it up and checked to see if there is a bias trim pot?
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Old 11-12-2012, 04:37 PM   #5
Unholy.Daemon
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Yeah, it's pretty hard to find any information on it.

Yeah, and the bias trim pot is on the back as well right below the probe points.
However, what I'm asking is if it's safe to just directly put in new tubes without rebiasing? Because I have no way of doing it myself, and it's not exactly convenient for me to take it down to the nearest tech.
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Old 11-12-2012, 04:56 PM   #6
KG6_Steven
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If you purchased tubes with the same rating, then you can install them. Installing and using the new power tubes without biasing the amp means you run the risk of them running too hot. Too hot is bad. They will end up wearing out much faster than they should, since the current is too high. If it's set too low, then the tone will be less than what it could be. Best to take that amp to a tech and have them bias it, or purchase the materials to do it yourself.

Some amps are designed to be tolerant of an incorrect bias setting, as the bias range is narrow. Not sure if yours is one them, or not.
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Old 11-12-2012, 05:11 PM   #7
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Quote:
Originally Posted by KG6_Steven
If you purchased tubes with the same rating, then you can install them. Installing and using the new power tubes without biasing the amp means you run the risk of them running too hot. Too hot is bad. They will end up wearing out much faster than they should, since the current is too high. If it's set too low, then the tone will be less than what it could be. Best to take that amp to a tech and have them bias it, or purchase the materials to do it yourself.

Some amps are designed to be tolerant of an incorrect bias setting, as the bias range is narrow. Not sure if yours is one them, or not.


i wouldn't know if they're the same rating, because the tech i took it too last time stuck some random tubes in there and gave it back to me, for some reason he put a 6L6 and an EL34 in, so no wonder the amp wasn't working properly.

but anyways, thanks for the advice, i'll see if i can get hold of a multimeter or take it to another tech
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Old 11-12-2012, 05:28 PM   #8
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He did what?! If the amp was being run with an EL-34 and a 6L6 at the same time, that's not real good. Those tubes operate at different voltages. Amps capable of running both will have a switch, which allows you to select one or the other. I wouldn't take it back to the same guy - he is clearly clueless.
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Old 11-12-2012, 05:30 PM   #9
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Quote:
Originally Posted by KG6_Steven
He did what?! If the amp was being run with an EL-34 and a 6L6 at the same time, that's not real good. Those tubes operate at different voltages. Amps capable of running both will have a switch, which allows you to select one or the other. I wouldn't take it back to the same guy - he is clearly clueless.


x2
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Old 11-12-2012, 05:34 PM   #10
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Just buy a cheap multimeter and bias it yourself. Simple.
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Old 11-12-2012, 05:36 PM   #11
R45VT
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Quote:
Originally Posted by Kevin Saale
Just buy a cheap multimeter and bias it yourself. Simple.


It has the adjustment and test ports on the back. Makes it super easy.
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Old 11-12-2012, 06:02 PM   #12
Unholy.Daemon
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yeah trust me, I don't plan on doing, besides he now lives 150 miles away ^^

that's the reason i was asking if it's ok though, because i just want to quickly swap the tubes and check that nothing inside the amp is damaged due to that.
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Old 11-12-2012, 06:07 PM   #13
R45VT
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Quote:
Originally Posted by Unholy.Daemon
yeah trust me, I don't plan on doing, besides he now lives 150 miles away ^^

that's the reason i was asking if it's ok though, because i just want to quickly swap the tubes and check that nothing inside the amp is damaged due to that.



A quick test shouldn't hurt anything. Can you see where your bias knob is at in the adjustment travel? You can always turn it down.
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Old 11-12-2012, 06:19 PM   #14
Unholy.Daemon
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Quote:
Originally Posted by R45VT
A quick test shouldn't hurt anything. Can you see where your bias knob is at in the adjustment travel? You can always turn it down.


ok thanks ^^

it seems about halfway, so yeah i'll turn it right down, running the tubes cold for a couple of minutes shouldn't do any damage hopefully
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