is it true that with the Classic 50 head, Classic 30 combo and the 5150 stack amps i own have no Bias adjustment for the tubes? If so i guess matched pairs of tubes is the best way to go...? getting time to retube almost all of them... in the late 90's i bought some plain un-matched Solvteck tubes and stuck them in as that is what a guy at Peavey told me to do...
Peavey amps Bias Question
- Thread starter WhoFan
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wixedmords
New member
Re: Peavey amps Bias Question
Depending on which version of the 5150 you have you may have a bias pot. The 2nd version has a bias pot. Either version has a "fixed" bias meaning they need to run at a specific bias and are not "bias free". But, Peavey usually sets them up cold so if you buy a set of "cold" tubes, you may be able to get away without biasing. But, it is always best to at least check the bias to make sure you aren't running too hot. It is easy to do, and I believe anything else is irresponsible. If you can bias the amp, you may not need cold tubes.
The Classis 50 head is fixed bias also, needing to be set to a specific bias, but I believe is non-adjustable. You would need to purchase cold tubes for that also.
Depending on which version of the 5150 you have you may have a bias pot. The 2nd version has a bias pot. Either version has a "fixed" bias meaning they need to run at a specific bias and are not "bias free". But, Peavey usually sets them up cold so if you buy a set of "cold" tubes, you may be able to get away without biasing. But, it is always best to at least check the bias to make sure you aren't running too hot. It is easy to do, and I believe anything else is irresponsible. If you can bias the amp, you may not need cold tubes.
The Classis 50 head is fixed bias also, needing to be set to a specific bias, but I believe is non-adjustable. You would need to purchase cold tubes for that also.
idsnowdog
Imperator of Indignation
Re: Peavey amps Bias Question
My answer may not be 100% correct. With fixed bias you usually need to buy a tube that performs as close to OEM specs as possible. Fixed bias amps can be modified to operate with adjustable bias or you can reset the bias by replacing certain components to bring them into the range you want.
The idea might be that with a fixed bias you can buy Peavey branded tubes and be assured of a certain level of performance. But I would think that from tube to tube there would still be enough variation that an amp might perform above or below expectations.
My answer may not be 100% correct. With fixed bias you usually need to buy a tube that performs as close to OEM specs as possible. Fixed bias amps can be modified to operate with adjustable bias or you can reset the bias by replacing certain components to bring them into the range you want.
The idea might be that with a fixed bias you can buy Peavey branded tubes and be assured of a certain level of performance. But I would think that from tube to tube there would still be enough variation that an amp might perform above or below expectations.
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Re: Peavey amps Bias Question
my 5150 is from the first year of issue.... the original 5150 with the Block EVH on the front.... When i got that amp and the Classic 50 head the manager of Peavey's old Canadian warehouse said i would be wise to get some new tubes right away.... he also said not to worry about getting it biased as they are fixed bias.... so i bought just solvtech tubes, un-matched pair tubes and stuck them in myself at home... that was 8-9 years ago and i'm thinking it's time i retube them the best i can
so is a Cold Tube mean it is running at a voltage range best suited for the amp? how do you know what the range would be? So buying a bunch of tubes in bulk and sticking them in is not the best way to do things with a fixed bias amp?
I hear good things about JJ tubes....
my 5150 is from the first year of issue.... the original 5150 with the Block EVH on the front.... When i got that amp and the Classic 50 head the manager of Peavey's old Canadian warehouse said i would be wise to get some new tubes right away.... he also said not to worry about getting it biased as they are fixed bias.... so i bought just solvtech tubes, un-matched pair tubes and stuck them in myself at home... that was 8-9 years ago and i'm thinking it's time i retube them the best i can
so is a Cold Tube mean it is running at a voltage range best suited for the amp? how do you know what the range would be? So buying a bunch of tubes in bulk and sticking them in is not the best way to do things with a fixed bias amp?
I hear good things about JJ tubes....
wixedmords
New member
Re: Peavey amps Bias Question
You are on on the track ID.
Fixed bias operates at a specific bias. Cathode bias operates within a range of bias, more specifically allowing a tube to operate safely when it comes within a specific range of bias. Cathode bias is more forgiving. Most of the time, a cathode biased amp doesn't need to have it's biased changed, but sometimes, on rare occasion, may have a bias adjuster.
Fixed bias amps also may or may not have a bias pot. If a fixed bias amp has no bias pot, you would have to buy a tube that operates within a certain bias range so you don't get too hot of a bias. In effect, you would need to fit the tube to the amp because it isn't adjustable. Another option is to change a resistor in the non-adjustable fixed bias amp to get the bias within proper range. Now, to really mix you up, a bias pot can usually be added to a fixed bias amp that doesn't have one.
The first generation 5150 was fixed bias, but had no bias pot. So, because we know a fixed bias amp needs to be set at a certain bias, we need to get a "cold" tube, add a bias pot, or change a resistor if it doesn't bias within a safe range.
The second generation 5150 (5150II) has a bias pot, and you can adjust the bias allowing you to bring the tubes with an acceptable range.
edited to delete an OTOH
You are on on the track ID.
Fixed bias operates at a specific bias. Cathode bias operates within a range of bias, more specifically allowing a tube to operate safely when it comes within a specific range of bias. Cathode bias is more forgiving. Most of the time, a cathode biased amp doesn't need to have it's biased changed, but sometimes, on rare occasion, may have a bias adjuster.
Fixed bias amps also may or may not have a bias pot. If a fixed bias amp has no bias pot, you would have to buy a tube that operates within a certain bias range so you don't get too hot of a bias. In effect, you would need to fit the tube to the amp because it isn't adjustable. Another option is to change a resistor in the non-adjustable fixed bias amp to get the bias within proper range. Now, to really mix you up, a bias pot can usually be added to a fixed bias amp that doesn't have one.
The first generation 5150 was fixed bias, but had no bias pot. So, because we know a fixed bias amp needs to be set at a certain bias, we need to get a "cold" tube, add a bias pot, or change a resistor if it doesn't bias within a safe range.
The second generation 5150 (5150II) has a bias pot, and you can adjust the bias allowing you to bring the tubes with an acceptable range.
edited to delete an OTOH
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Binnerscot
Active member
Re: Peavey amps Bias Question
The colder bias means you have a little more room to move with tubes. It is somewhat difficult to get tubes that are too "hot" for a fixed (cold) bias amp. In fact, the Triple X trim pot is usually set wide open with 6L6s.
The only time you would run into issues would be the case of a Triple X running EL34s - it is possible to get them too hot.
Modern amps are designed to plug and play the average spec tube off the shelf.
The colder bias means you have a little more room to move with tubes. It is somewhat difficult to get tubes that are too "hot" for a fixed (cold) bias amp. In fact, the Triple X trim pot is usually set wide open with 6L6s.
The only time you would run into issues would be the case of a Triple X running EL34s - it is possible to get them too hot.
Modern amps are designed to plug and play the average spec tube off the shelf.
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wixedmords
New member
Re: Peavey amps Bias Question
The easy way out is to contact one of the tubes sellers and ask for cold tubes. Explain to them your situation.
The 5150's I have seen have been biased cold to start with, so you may be able to get away with hotter tubes. But, you will never know what the bias is without checking.
The easy way out is to contact one of the tubes sellers and ask for cold tubes. Explain to them your situation.
The 5150's I have seen have been biased cold to start with, so you may be able to get away with hotter tubes. But, you will never know what the bias is without checking.
wixedmords
New member
Re: Peavey amps Bias Question
Sorry Bro. That's not completely true, but In understand where you are coming from.
They may be designed around modern tubes, which are easier to get and less expensive than NOS, but not specifically designed around plug n' play.
Biasing cold and not giving you an adjustment stops uneducated hands from biasing by ear or by eye, or even by smell (that one kills me). As an example, George Lynch had some issues biasing by ear on his gear page, and biasing by eye (color) is inaccurate because a tube will usually red plate when it is far out of an acceptable bias setting.
Sorry Bro. That's not completely true, but In understand where you are coming from.
They may be designed around modern tubes, which are easier to get and less expensive than NOS, but not specifically designed around plug n' play.
Biasing cold and not giving you an adjustment stops uneducated hands from biasing by ear or by eye, or even by smell (that one kills me). As an example, George Lynch had some issues biasing by ear on his gear page, and biasing by eye (color) is inaccurate because a tube will usually red plate when it is far out of an acceptable bias setting.
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Re: Peavey amps Bias Question
i have to say that other 5150's always seem slightly sweeter then mine... since the day i bought it... A friend has one that is an early issue as well, his is beat to snot, has many man hours of playing time on it, yet sounds great even with all the jack shorts and pot noise!!!! His is more open on the low end and sounds slightly crunchier.
i have to say that other 5150's always seem slightly sweeter then mine... since the day i bought it... A friend has one that is an early issue as well, his is beat to snot, has many man hours of playing time on it, yet sounds great even with all the jack shorts and pot noise!!!! His is more open on the low end and sounds slightly crunchier.
Binnerscot
Active member
Re: Peavey amps Bias Question
^Very true...you may want to get the specs, whether yourself with a meter (careful with that one) or have a tech do it. Just to see where it sits.
^Very true...you may want to get the specs, whether yourself with a meter (careful with that one) or have a tech do it. Just to see where it sits.
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wixedmords
New member
Re: Peavey amps Bias Question
I don't want to specifically point to a hotter bias equaling a sweeter sound, because sound is so subjective. Everyone has a sound they like. But, if you had adjustability built into the bias circuit, you could bias the amp to what sounds sweeter to your ear, as long as you stay with safe ranges.
On the obvious side, if the power tubes in the amp are really old, new ones will likely sound better anyway.
There are many factors why your friends 5150 sounds so sweet. The easiest one it to find out what tubes he is running, specifically the preamp tubes (preamp tubes don't need biasing), and try the same in yours.
I don't want to specifically point to a hotter bias equaling a sweeter sound, because sound is so subjective. Everyone has a sound they like. But, if you had adjustability built into the bias circuit, you could bias the amp to what sounds sweeter to your ear, as long as you stay with safe ranges.
On the obvious side, if the power tubes in the amp are really old, new ones will likely sound better anyway.
There are many factors why your friends 5150 sounds so sweet. The easiest one it to find out what tubes he is running, specifically the preamp tubes (preamp tubes don't need biasing), and try the same in yours.
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Binnerscot
Active member
Re: Peavey amps Bias Question
Without getting too wordy, most "adjustable" bias amps (fixed bias with a trim pot) are set at points that well within a "safe" range for most tubes.
There is an ideal point mathematically for power tube operation depending on the circuit (see formula from sig above). Less than this is said to be cold, and more is said to be hot. Hot means you will run the risk of tube and/or circuit failure. Read up on your amp from as many places as you can, you may want to check the peavey forum...there is some bias info there also.
When you have a trim pot and test points, the ideal setting according to the manufacturer will most likely be on the cold side. The trim pot operates from colder to cold, and usually doesn't get to the ideal setting. Hotter tubes will get you closer. Example, hot tubes in the Triple X with the setting maxed, gets you close to the ideal point.
Is your friends 5150 a 2x12 combo? Those are noted to be biased a little warmer than the heads and most agree that they sound just a little "sweeter".
Without getting too wordy, most "adjustable" bias amps (fixed bias with a trim pot) are set at points that well within a "safe" range for most tubes.
There is an ideal point mathematically for power tube operation depending on the circuit (see formula from sig above). Less than this is said to be cold, and more is said to be hot. Hot means you will run the risk of tube and/or circuit failure. Read up on your amp from as many places as you can, you may want to check the peavey forum...there is some bias info there also.
When you have a trim pot and test points, the ideal setting according to the manufacturer will most likely be on the cold side. The trim pot operates from colder to cold, and usually doesn't get to the ideal setting. Hotter tubes will get you closer. Example, hot tubes in the Triple X with the setting maxed, gets you close to the ideal point.
Is your friends 5150 a 2x12 combo? Those are noted to be biased a little warmer than the heads and most agree that they sound just a little "sweeter".
Re: Peavey amps Bias Question
Thanks for the info... The tubes in mine have been there 8-9 years maybe if i do my math right.... But i have not used it much, mostly just for band work. i gigged a bit with it... But it should be retubed..... I think my friends 5150 has stock well used Peavey tubes in it....
Thanks for the info... The tubes in mine have been there 8-9 years maybe if i do my math right.... But i have not used it much, mostly just for band work. i gigged a bit with it... But it should be retubed..... I think my friends 5150 has stock well used Peavey tubes in it....
Re: Peavey amps Bias Question
My buddies 5150 set up is the same as mine..... early issue original 5150 head with the EVH block logo, and a straight front 5150 cab
My buddies 5150 set up is the same as mine..... early issue original 5150 head with the EVH block logo, and a straight front 5150 cab
wixedmords
New member
Re: Peavey amps Bias Question
I believe the head is fixed bias and the C30 is cathode biased, but you should double-check that information. While it is not where I go, the Tube Store seems to have some fans here. I would email the website and see what they recommend.
I believe the head is fixed bias and the C30 is cathode biased, but you should double-check that information. While it is not where I go, the Tube Store seems to have some fans here. I would email the website and see what they recommend.
