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Old 10.03.12, 7:46 PM
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Using unmatched 6L6 power tubes.

Hi everybody,

I need to change my power tubes and I have a quad of sovtek 6L6'S but they are unmatched can I still use them? Also when biasing them will I need to bias each one individually because they are unmatched. Any advice anyone can offer will be appretiated.
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Old 10.03.12, 9:34 PM
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Question is, how unmatched are they??? Is it two sets, or just individuals? Most high wattage amps are push pull, so you can get away with mismatched, as long as they're in sets. Also, what amp? I don't see how you could bias each tube.....
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Old 10.04.12, 5:42 AM
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Hey Supergrunged,

They are actually 2 sets, sorry I should have said that. I will be using them in a bugera 333. Also am I to understand that once the bias is set for 1 tube that it's set for all 4?

Last edited by station5343; 10.04.12 at 5:48 AM.
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Old 10.04.12, 11:17 AM
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There isn't a screen grid for each tube, they work in sets. Typically, it'll be the two outer tubes are one set, and the two center tubes. There is only one bias pot to my knowledge, some have two for the sets, I've never seen one for each on of them... You can test each set, and find the middle ground for both of them. I'm sorry, I'm not to familiar with that amp.

Just watch out, there's high voltages in the amp that can kill you if you're not careful
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Old 10.04.12, 12:57 PM
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The amp will not be damaged unless the tubes are red plating. A lot of people like the sound of mid-matched tubes because of asymmetric clipping. However, the amp may sound different to you because of that or because the tubes are biased a little hot or colder compared to the previous set. If you post an the Ampage site you will probably get a more complete answer from a Bugera authorized tech.
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Old 10.06.12, 1:14 PM
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Are you still dealing with this.?
Have you ever biased an amp before.?
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Old 10.12.12, 9:11 PM
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Hello again everyone,

In reference to my post on biasing an amp and using unmatched power tubes. Is it safe to do this? Say for example 2 sets of 6L6'S one set with a plate voltage reading of 23.0 and the other 36.0 would it be ok to set the bias the same for both sets? If anyone who reads this knows the answer please feel free to post a reply...thanks.

Last edited by station5343; 10.12.12 at 9:17 PM.
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Old 10.13.12, 2:15 AM
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Quote:
Originally Posted by station5343 View Post
Hello again everyone,

In reference to my post on biasing an amp and using unmatched power tubes. Is it safe to do this? Say for example 2 sets of 6L6'S one set with a plate voltage reading of 23.0 and the other 36.0 would it be ok to set the bias the same for both sets? If anyone who reads this knows the answer please feel free to post a reply...thanks.
How are you going to do that.?
Does your amp have dual bias.?
If so.....
If one pair runs at 23mA and the other at 36mA (not Volts you say) then they ARE matched.
Run one set together and the other together. That is, put one pair in the Inside/Outside position, and the other pair in the opposite.
best
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Old 10.13.12, 5:32 AM
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Thanks trem,

That makes sense, so my next question is what about using individuals that aren't in sets? Olddawg posted a reply saying that it can be done as long as the tubes dont red plate. How do I keep the tubes from red plating?
Thanks
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Old 10.13.12, 11:48 AM
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Keep the voltage down.... You don't want to cook your tubes..... Basically it's ohms law, if you're not familiar with Ohms law, I don't recommend even attempting it. Yea, there's a knob on the outside of the chassis to adjust it, with a place to put your probes, just like a 5150 II.... I still don't trust these things. You need to know the power, which is measured in watts..... So you have a 100 watt rated amp, you want to bias the tubes for 70 watts, that would be 70 percent, and they should last you for a couple years. The equation is P=I R, so if you know the resistance of the tube, and you know the wattage you need, all you need to figure out is the amperage you need to set the tubes for.

It's a fun process, and if you're familiar with electronics, resisitive loads, the basics of all components, I say try it. If you're just trying to save a buck by buying a multimeter, and thinking the probes on the back do the work, look into sending the amp to a tech to get it biased properly
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Old 10.14.12, 4:13 PM
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Quote:
Originally Posted by station5343 View Post
Thanks trem,

That makes sense, so my next question is what about using individuals that aren't in sets? Olddawg posted a reply saying that it can be done as long as the tubes dont red plate. How do I keep the tubes from red plating?
Thanks
Seriously.?
At your level of understanding......
Just buy a quad of matched tubes. Why the question about 4 un-matched power tubes. I thought you had two matched pairs with a dual bias amp.?
Good Luck
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Old 10.14.12, 4:31 PM
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Quote:
Originally Posted by trem View Post
Seriously.?
At your level of understanding......
Just buy a quad of matched tubes. Why the question about 4 un-matched power tubes. I thought you had two matched pairs with a dual bias amp.?
Good Luck
Well ok then trem, (Mr know it all)

I thought this was supposed to be a place to get advice, not to be insulted. Maybe we dont all know as much as you do so if you dont have anthing constructive to offer then I would appretiate it if you dont reply to my post. Maybe I have several different amps that I want to change the tubes in, hense the question about using unmatched tubes if you really need to know.
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Old 10.14.12, 4:50 PM
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I am not insulting you.
You said nothing about multiple amps and more tubes. I naturally assumed you were discussing the same issue.
But, I can tell you, by the questions you are asking, you are not ready to attempt biasing a quad of unmatched power tubes.
Have you ever biased an amp at all.?
You would be better off, IMHO, to buy a matched quad and learn how to bias a "normal" amp.
Otherwise, it depends on how "unmatched" (you do not say) the power tubes are.
Far enough off and you can have all kinds of noise/hum issues, or even drive tubes into red-plating while others are in cut-off.
Do yourself a favor. Learn how to properly bias a normally functioning amp before you worry about all this other "stuff".
Good Luck
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  #14  
Old 10.14.12, 6:45 PM
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Quote:
Originally Posted by trem View Post
I am not insulting you.
You said nothing about multiple amps and more tubes. I naturally assumed
@ Trem - The poster did mention the amp, as a Bugera 333, a quick internet search on google can bring up the manual, and the fact that it has an external bias trim pot, just like a 5150 II or a 6505+. A google search typically takes less then 3 seconds. This is a place of information... Agreed, the OP should probly bring their amp to a tech, no need to insult their intelligence though.

@ station5343 - Just bite the bullet and buy a matched quad, I've found Ruby 6L6 tubes for around 62 bucks (USD) for a matched quad from a mom and pop store. Tube amps are something you shouldn't cheap on, or they'll cheap out on you.... olddawg knows this from experience with the old Silvertones of the 60's and 70's........

You can get by with an unmatched set, provided the amp is biased correctly, even then, a certified tech should do it. I'd say keep the unmatched set as spares. Biasing an amp is fun, and looks easy on paper, but the capacitors in your amp, if they still have a charge, and you touch them, can kill you. It can take about a month or longer for those caps to discharge the voltage in them. I've biased a couple amps myself, but I wouldn't recommend it to anyone without proper electrical precautions... IE meaning, you know the difference in low voltage and high voltage, have experience with transformers, know what rectifiers are, all that jazz.

I am familiar with residential wiring, and the NFPA article 70. Most bench techs would have to know a little about the NEC. OSHA rules require protective gear for anything above 300 volts..... You don't know any of these things? I DON'T RECOMMEND BIASING YOUR AMP!!!! You'll fry the tubes, the amp, or yourself if you don't know EXACTLY what you are doing. Best of luck
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