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Post by shredesis on Sept 8, 2004 20:01:42 GMT -5
I have a bum tube in my 5150 w/ bias. If i want to put new tubes in, should i just buy some 6l6's which are whats in it, and plug em in? Or do i need to adjust the bias or anything like that? Also, the back of the amp says all tubes 12xa7 but the tubes are 6l6's? And where are the pre amp tubes located? This is my first tube amp and I'm not sure about the innerworkings yet. Thanks.
P.S I'm thinking of JJ's for the new tubes since it seems everyone likes them.
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Post by Jerry P on Sept 8, 2004 21:24:25 GMT -5
I have a bum tube in my 5150 w/ bias. If i want to put new tubes in, should i just buy some 6l6's which are whats in it, and plug em in? Or do i need to adjust the bias or anything like that? Also, the back of the amp says all tubes 12xa7 but the tubes are 6l6's? And where are the pre amp tubes located? This is my first tube amp and I'm not sure about the innerworkings yet. Thanks. P.S I'm thinking of JJ's for the new tubes since it seems everyone likes them. You should always have an amp biased after changing power amp tubes. That sets the operating point for the power tubes so you can get the best tone and life from your tubes. This also gives a tech a chance to give your amp a cleaning and check it over for problems that you might not be aware of. The way Peavey makes the 5150 with the bias so cold you can usually get away with just popping in a set of tubes. By doing this you're not gonna get everything your tubes have to offer and you'll never know of problems within the amp unless a tech gets in there. Since you have the bias mod you should have it biased to be safe. I love the JJ power tubes for the 5150's. Jerry |
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Post by shredesis on Sept 14, 2004 17:12:52 GMT -5
I don't think I understand what you mean by "biased." Wouldn't having the amp biased again make the bias mod pointless? And not to sound like a complete retard more, but what exactly is the point of the trim pot in the bias mod? Is it so you can manually adjust the bias yourself or what? I guess I'm just under the impression that you can just pop new tubes in whenever old ones go out.
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Post by Jerry P on Sept 14, 2004 19:04:58 GMT -5
The 5150 comes stock with the bias not adjustable. In order for a tech to make adjustments he must either go in and replace resistors to get the proper bias voltage or install a bias pot so the bias can be adjusted. The bias pot is smarter because once it's done all future biasing will easier and cost less because no circuit mods will be required.
The 5150 come with a very cold bias stock and it does allow you to just pop tubes in. You won't get the most out of your tubes tone wise unles they are properly biased. Since your amp has already been modded with the bias pot you really should have it checked when you install new power tubes.
Jerry
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Post by A&Z Guitar Repair on Sept 15, 2004 21:18:02 GMT -5
Jerry, what's the acceptable bias points for the 5150/5150II's? Any guidelines or suggestions...?
Thanks.
Scott Eivins
A&Z Guitar Repair
Now Selling Krank Amps
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Post by Jerry P on Sept 16, 2004 0:43:44 GMT -5
Jerry, what's the acceptable bias points for the 5150/5150II's? Any guidelines or suggestions...? Thanks. Scott Eivins A&Z Guitar Repair Now Selling Krank Amps I set every amp different. I go by what I see on the scope, what I read on the ammeter, and what I hear with my ears. I also take into account what type of tone the player is looking for. Colder makes it tighter and faster, hotter makes the tone warmer and bigger. I usually end up somewhere between 32-38ma. Jerry |
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Post by Raf on Sept 23, 2004 23:44:07 GMT -5
I have a quick question about biasing Jerry. Lets say I am ready to change the bias on my amp. When I flip the Standby to On the current on the DMM using the bias probe is for example 28mA. But what I noticed that if the amp is in the ON position for a while (just to see if everything is fine) that current climbs by about 10mA to around 36-38mA and stays there. My question is, when you state I like to bias it at 32mA - 38mA which case is it?
Thank You
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Post by Jerry P on Sept 24, 2004 0:41:59 GMT -5
I have a quick question about biasing Jerry. Lets say I am ready to change the bias on my amp. When I flip the Standby to On the current on the DMM using the bias probe is for example 28mA. But what I noticed that if the amp is in the ON position for a while (just to see if everything is fine) that current climbs by about 10mA to around 36-38mA and stays there. My question is, when you state I like to bias it at 32mA - 38mA which case is it? Thank You I'm not sure I follow you 100% on what you're saying in the first part there. The amp has to be on a little while for the tubes to warm up and stabablize themselves. There's is no set magic number for bias. Bias is a range. The point is to be within the safe bias range and get the best tone within that range. Some amps it's 32 others it might be 38. It depends on the music the player is playing too. Some guys want it fatter and warmer while other may want it tighter and faster. I look at the current draw of the tubes, look at what it looks like on my scope, and listen with my ears. That's how I bias an amp. Jerry |
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