Biasing question- Very Important


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patriotplayer90
06-18-2008, 11:26 PM
I just got a Peavey Triple XXX head, and it allows the option to adjust between biasing for 6l6 tubes or EL34's. The guy i bought it from said he put EL34's in it, but i looked at the bias switch and it was pointed to 6l6.

What is the danger of having EL34 tubes in while the bias is set to 6l6?

HavokStrife
06-18-2008, 11:44 PM
Are you sure this guy knows what he's talking about?

Are you sure that the switch just didn't get pushed in your car or however you transported it?

Physically read the tubes, see what they are, set switch to that bias, turn on, if it works, you probably got nothing to worry about.

Erock503
06-18-2008, 11:53 PM
I just got a Peavey Triple XXX head, and it allows the option to adjust between biasing for 6l6 tubes or EL34's. The guy i bought it from said he put EL34's in it, but i looked at the bias switch and it was pointed to 6l6.

What is the danger of having EL34 tubes in while the bias is set to 6l6?
Not completely sure, but I don't think anything as long as the tubes were biased correctly. It still has a bias pot, the switch just bumps up the range of the pot higher for EL34 iirc. If he just moved the switch over without biasing, the 6L6 are probably running hot.

patriotplayer90
06-18-2008, 11:54 PM
I checked and saw there were EL34 tubes in it, and the switch was set to 6l6. I changed it and it made a HUGE difference in sound. There is alot more clarity and it just overall sounds 20 times better

Erock503
06-18-2008, 11:57 PM
I checked and saw there were EL34 tubes in it, and the switch was set to 6l6. I changed it and it made a HUGE difference in sound. There is alot more clarity and it just overall sounds 20 times better
oops, just realized I read that wrong, you had EL34 and the switch at 6L6. Yeah, the EL34 were probably running cool before then, the EL34 setting bumps up the bias range higher.

Van Noord
06-19-2008, 10:53 AM
Now you can adjust the bias trim pot dial for further control.

patriotplayer90
06-19-2008, 05:40 PM
Now you can adjust the bias trim pot dial for further control.

I saw that dial but was not quite sure what it did so i left it about half way. How would adjusting this affect the sound?

Van Noord
06-20-2008, 02:07 PM
I saw that dial but was not quite sure what it did so i left it about half way. How would adjusting this affect the sound?This dial allows the player to have a small window of adjustment for how hot they want to run the poweramp. When standing behind the amp, turning the dial counter clockwise makes the poweramp run hotter, allowing for more saturation and a thicker sound. Turning the dial clockwise makes the poweramp run cooler.
I have the bias dial on my JSX set to approx. 11 o' clock and love the results.

I've talked to Peavey and the entire sweep of this dial is safe to use at any position so there's no need to worry about causing any harm. Also, the further counter clockwise you turn it, the more noise your amp might start may start making. (because the amp is running hotter) so you just have to find that happy medium. You can turn the dial slowly while playing the amp so you can hear the impact of where you set the dial. It's a very cool feature. I find it helps you get that "poweramp thump" better and does wonders for getting those deep, thick sounding palm mutes.

Johnbryant
06-20-2008, 02:36 PM
I really think you should ethier have the amp biased by a tech, or bias it yourself. All you will need is a bias probe (25 dollar tool) and a Muti-meter, the XXX with EL34s should be biased 32-40 mhA. I read the test points on the back of the amp are not accurate with EL34s. Plus the bias knob should not be messed with unless you know how to bias and have a bias probe. It even says on the amp or the manual that biasing should be preformed by a tech, that knob should not be tuched if you don't know what you are doing. The XXX and the JSX have more than enough adjustment with the bias knob to ruin a set of EL34s I don't care what Peavey says. If you want to try to use the test points Peavey recomends 42.5 volts at the points for EL34, although I have read that is way to hot with some tubes. I recomend getting a bias probe and doing it your self, thats what I do.

MrCarrot
06-20-2008, 02:52 PM
I really think you should ethier have the amp biased by a tech, or bias it yourself.:haha:haha:haha

As opposed to what, having it biased by farmyard animals?

Johnbryant
06-20-2008, 02:55 PM
^ I ment If he didn't know what he was doing he should take it to an amp tech to bias it.

I see how what I said could be viewed as somthing funny though, LOL

Van Noord
06-20-2008, 05:02 PM
I really think you should ethier have the amp biased by a tech, or bias it yourself. All you will need is a bias probe (25 dollar tool) and a Muti-meter, the XXX with EL34s should be biased 32-40 mhA. I read the test points on the back of the amp are not accurate with EL34s. Plus the bias knob should not be messed with unless you know how to bias and have a bias probe. It even says on the amp or the manual that biasing should be preformed by a tech, that knob should not be tuched if you don't know what you are doing. The XXX and the JSX have more than enough adjustment with the bias knob to ruin a set of EL34s I don't care what Peavey says. If you want to try to use the test points Peavey recomends 42.5 volts at the points for EL34, although I have read that is way to hot with some tubes. I recomend getting a bias probe and doing it your self, thats what I do.Umm, no.

The test points on the back of these amps have nothing to do with biasing the amp. The amp has to be opened up in order to be properly biased. The supplied bias trim pot is absolutely safe to adjust yourself as it's sweep is short and can no way harm the amp. Again, this is from the horse's mouth and I've tested this multiple times. A tech will not use the test points at the back or the trim pot. A tech will open the amp up to access the full range of the trim pot.
Ruin a set of EL34's by turning the trim pot??? Where did you come up with that?? It's just simpley not true.

Johnbryant
06-21-2008, 12:06 AM
Umm, no.

The test points on the back of these amps have nothing to do with biasing the amp.
Then Why does it say BIAS TEST right on the back of the amp directly under the test points?... I find it kinda odd that they have nothing to do with the bias..... :no:

Here is what I found:
Enter the Triple X. Peavey was listening... The bias sweep on this amp can get either a quad of 6L6's or E34L's up to the proper bias level and if you really want to know what the bias is set at I would suggest you get a bias probe to check it with because the test points on the amp are measuring voltage and not plate current. I cannot stress enough how inaccurate the test points are! We just retubed a pair of JSX heads that were modded by Voodoo amps including the Mercury Magnetics VA-JSX-0 output trannys and because we get asked about the bias test points everyday we decided to document the readings for you. Running KT77's in the EL34 mode with a probe installed and the bias set to 36mA the test points measured 45 volts. Then we turned the bias down to a cold 20mA and the voltage at the test points read 48 volts. So a difference of 16 milliamps measured with a bias probe only showed a 3 volt difference at the test points!

An update 10/09/07 We just measured the bias on a XXX in the EL34 mode and with the bias set at 42 volts using the factory test points (Peavey recommends 42.5) the bias was a whopping 57mA which is over 100% of dissipation! You will burn up your tubes with all but the coldest grades of EL34's or KT77's. With the bias set to 45 volts at the factory test points the bias went way down to a very acceptable 37mA. So in this particular amp a variation of only 3 volts at the factory test points made an incredible 20mA difference in bias!!

Do NOT bias your XXX or JSX for any EL34 type tube including the JJ KT77's using the test points! The 55 volts that Peavey recommends at the test points for 6L6GC's is on the other hand, on the cool side but using the test points is so completely inaccurate we will not warrantee tubes to players who use the test points to bias these amps!

I just read a statement that was posted on the Peavey forum (yes, I was lurking...) and it stated that the bias on the XXX did not have enough range to get the power tubes too hot. This is not true!! There is plenty of adjustment especially in the EL34 mode to fry any tube!

This from Euro tubes, heres the link. http://www.eurotubes.com/euro-k.htm

Van Noord
06-23-2008, 12:31 PM
Yes, I know all about Bob's public distaste for Roger Crimm and Peavey. It has generated a largely negative perception of Bob's ability to conduct professional business in a mature manner. But that's neither here nor there.

The test points measure voltage not current, correct. You have to adjust the bias the same way as any amp.

Also, Bob is a E34L distributor and fanboy. These are not the same as EL34's. They have a much higher plate voltage and only JJ Tesla sells these out of the ordinary tubes.

Bloodshed
06-23-2008, 12:33 PM
Umm, no.

The test points on the back of these amps have nothing to do with biasing the amp. The amp has to be opened up in order to be properly biased. The supplied bias trim pot is absolutely safe to adjust yourself as it's sweep is short and can no way harm the amp. Again, this is from the horse's mouth and I've tested this multiple times. A tech will not use the test points at the back or the trim pot. A tech will open the amp up to access the full range of the trim pot.
Ruin a set of EL34's by turning the trim pot??? Where did you come up with that?? It's just simpley not true.


Not true. You can bias with a bias probe, which sits in the tube socket underneath a tube. The trimpot on the XXX is on the outside of the chassis, meaning it can stay in the case.

Also Bob does sell EL34s and E34Ls. And the factory test points are extremely inaccurate. I have tested this myself on my friends XXX. Using a bias probe you will get a much more accurate reading

Van Noord
06-23-2008, 12:45 PM
Not true. You can bias with a bias probe, which sits in the tube socket underneath a tube. The trimpot on the XXX is on the outside of the chassis, meaning it can stay in the case.

Also Bob does sell EL34s and E34Ls. And the factory test points are extremely inaccurate. I have tested this myself on my friends XXX. Using a bias probe you will get a much more accurate readingLike I said, you have to bias these amps at the tube sockets and the trim pot that is accessable is of limited sweep. The full range can be attained if open the amp up and turn the bias screw. Sometimes that's necessay, other times it's not. Of course the test points are inaccurate, they measure voltage, not current. I wouldn't take everything Bob says as the end all truth either. He can be quite vindictive. Just saying...

Johnbryant
06-23-2008, 12:55 PM
Also, Bob is a E34L distributor and fanboy. These are not the same as EL34's. They have a much higher plate voltage and only JJ Tesla sells these out of the ordinary tubes.

Yeah, I was told directly by a service rep at peavey that E34L grid voltage was to high for the XXX and would fry a grid resistor. Although the newer XXX heads and JSX come with upgraded resistors the peavey service rep still recomended the standard El34s over the E34L for a the XXX/JSX amps. All tubes stores should really put a disclaimer about the E34L and compatability issues with XXX series.

On a side not I wonder if euro tubes where using the E34l when testing, if so that might expain the inacuracy of the test point readings. Just a Thought...

MrCarrot
06-23-2008, 01:13 PM
Yeah, I was told directly by a service rep at peavey that E34L grid voltage was to high for the XXX and would fry a grid resistor. Although the newer XXX heads and JSX come with upgraded resistors the peavey service rep still recomended the standard El34s over the E34L for a the XXX/JSX amps. All tubes stores should really put a disclaimer about the E34L and compatability issues with XXX series.

On a side not I wonder if euro tubes where using the E34l when testing, if so that might expain the inacuracy of the test point readings. Just a Thought...wait, what? How is its "grid voltage too high"? If it can run 6L6s then I doubt an EL34 variant will pull an excess of current in comparison?

Johnbryant
06-23-2008, 01:26 PM
wait, what? How is its "grid voltage too high"? If it can run 6L6s then I doubt an EL34 variant will pull an excess of current in comparison?
All I know is what Peavey Rep said and this info I got from the tubedepot: (With a slightly higher grid voltage (-13.5 to -16.5 vs -10 to -13.5 volts for the EL34) than other EL34 / this tube offers tight low end with smooth mids. ) Acording to Peavey the XXX uses a 100 Ohm grid resistor, and I know that typical El34 amps use a 1kohm grid resistor, newer xxx amps are upgraded with 740ohm resistor. As far as grid voltage goes and comparing 6l6 to El34 and I would not know, but I know the XXX and JSX have switch that alows you to switch from 6l6 and EL34s.
This is my thoughts on the hole E34l situation, if I bought a new Ford tuck, and Ford said not to use a certain oil per say becasue it could cause failer, I would not use that oil. Same goes with my amp, if Peavey says that the E34l are not compatable then I will find somthing else to use, its that simple.

Van Noord
06-23-2008, 02:37 PM
This is my thoughts on the hole E34l situation, if I bought a new Ford tuck, and Ford said not to use a certain oil per say becasue it could cause failer, I would not use that oil. Same goes with my amp, if Peavey says that the E34l are not compatable tubes then I will find somthing else to use, its that simple.+1. I'm perfectly happy with standard EL34's in my JSX.

MrCarrot
06-23-2008, 02:53 PM
All I know is what Peavey Rep said and this info I got from the tubedepot: (With a slightly higher grid voltage (-13.5 to -16.5 vs -10 to -13.5 volts for the EL34) than other EL34 / this tube offers tight low end with smooth mids. ) Acording to Peavey the XXX uses a 100 Ohm grid resistor, and I know that typical El34 amps use a 1kohm grid resistor, newer xxx amps are upgraded with 740ohm resistor. As far as grid voltage goes and comparing 6l6 to El34 and I would not know, but I know the XXX and JSX have switch that alows you to switch from 6l6 and EL34s.
This is my thoughts on the hole E34l situation, if I bought a new Ford tuck, and Ford said not to use a certain oil per say becasue it could cause failer, I would not use that oil. Same goes with my amp, if Peavey says that the E34l are not compatable then I will find somthing else to use, its that simple.I'm only making a point of this as it seems wrong to me fundamentally although i'm sure somebody may correct me (SYK?)... Isn't the grid voltage determined by the setting of the bias resistor? And the screen grid resistor is to protect the power tube? it doesn't really drop much voltage....

Johnbryant
06-23-2008, 03:07 PM
+1. I'm perfectly happy with standard EL34's in my JSX.
What seting is your bias knob set at with your tubes? And what brand of tubes are you useing?

Van Noord
06-23-2008, 04:23 PM
What seting is your bias knob set at with your tubes? And what brand of tubes are you useing?I have put Svetlana EL34's in my JSX and I have the bias dial set to approx. 11 o' clock.