6l6gc's in El34 mode

[ScreaminSaint]

there has been talk on other forums that you can run 6l6's in el34 mode. that is with tube/bold settings. anyone familiar with this?

 

[Boogiebabies]

I bought a set of # 26 6L6's from Bob at Euro tubes. In the 6L6 setting it pulls around 17ma. With the EL34 setting it pulls 40ma. It's just just a way to get a good bias on the 6L6 without having to put a very hot 6L6 in.
It's a very fat tone and totally within the safe range.

 

[Guitarzan]

I bought a set of # 26 6L6's from Bob

Ok...here's the dilemma. How does JJ arrive at a #26 or #44 or #42? Is there a rating chart? Does a #26 = a Groove Tube #7? Basically, does the lower numbers = a cooler running tube? I've only seen plate voltage matched JJ's which we get from CE distribution.

 

[Boogiebabies]

JJ does not. Bob @ Eurotubes matches his own tubes and puts a rating on them. 26 is the natural current draw of the tube. It's in the cooler range so you can use the EL34 bias switch with provides much more negative voltage than the 6L6 side, thus biasing the tube close to MPD.

Tubes are matched based on their natural current draw and sometimes their transconductance. Most tube vendors check them even after they are matched at the factory with a Maxi Matcher. Some vendors like Triode Electronics and Lord Valve burn in the tubes for 24 hours and then rematch them. I have a three sets of 6L6's and EL34 Svetlana's that I bough from Triode. After 2 years of moderate use the have not drifted a single .ma since they were new. Tight matching and screening !!!!

I dont get what you mean by plate voltage matching. It is only one part of properly biasing a tube. Everyone uses different numbers like GT's # 7 just means that once you bought them and biased the amp you dont have to when you replace the tubes with the exact same # 7 GT tube.


www.eurotubes.com

Call Bob, he has done a bunch of testing on DR's with JJ's.
Check out his Mesa Boogie link.

If you want to play the gussing game with Antique Electronic Supply or
Groove Tubes you will need a bunch of different ratings to try and plate voltage readings. You wil also need a bias meter.

Eurotubes.com is down at the moment.

 

[Guitarzan]

It looks as if I'm going to have to invest in a bias meter (bias rite) or equivalent. I never know what I'm going to get from CE/Antique. The way our local tech has been doing the biasing is running a audio signal generator to the input of the amp, o-scope to the positive of the load of the speaker outs (w/load attached) and adjusting for the best sine wave before clipping. How do you feel about this?

 

[MesaDCLP]

Is there a rating chart?

... for JJ that competes with other vendors ???

could i run a Mesa Red 6L6 on the el34 setting ...

or

could i run a Mesa White 6L6 on the el34 setting ???

OR

What GT 6L6 is safe in el34 mode ???

 

[Boogiebabies]

It looks as if I'm going to have to invest in a bias meter (bias rite) or equivalent. I never know what I'm going to get from CE/Antique. The way our local tech has been doing the biasing is running a audio signal generator to the input of the amp, o-scope to the positive of the load of the speaker outs (w/load attached) and adjusting for the best sine wave before clipping. How do you feel about this?

IMO, this does not take into account what % of MPD yor tubes are running.
Depending on the natural current draw of your tubes, you could be running your tubes at 85% MPD to get out of crossover distortion.
Also, if you dont have an adjustable bias, how is he going about this?

 

[Guitarzan]

He uses this method for amps with bias adjusts. The fixed bias stuff he just recommends GT's 4-7. I was skeptical of the adjustments he was making with this method. He seems content with it. I do see your point and I would feel MORE comfortable using the meter and the math. What are you using?

 

[Boogiebabies]

Is there a rating chart?

... for JJ that competes with other vendors ???

could i run a Mesa Red 6L6 on the el34 setting ...

or

could i run a Mesa White 6L6 on the el34 setting ???

OR

What GT 6L6 is safe in el34 mode ???

With Mesa color codes you have to have a bias meter, the Yellow 6L6's only draw are 17ma so they should be able to handle it, but Red is a maybe and White is a definite no. You need a bias meter and experiment with color codes.

Remember, Mesa's are design for huge headroom and the hotter you bias them the less headroom you will have. I generally never go over 35ma or they get too mushy and loose headroom. The GT's are the same thing. They may have a rating, but it means nothing about what it will bias at in your amp. Different tubes act differently at the same negative voltage. Tubes with higher natural plate current tend to draw more bias and a KT66 will draw differently than a 6L6 or EL34. Without a bias meter and plate voltage readings its a crap shoot. i personally am not a big proponent of biasing DR's towards 75% of MPD. I think they sound fine between 22 and 30 ma.

 

[Boogiebabies]

He uses this method for amps with bias adjusts. The fixed bias stuff he just recommends GT's 4-7. I was skeptical of the adjustments he was making with this method. He seems content with it. I do see your point and I would feel MORE comfortable using the meter and the math. What are you using?

I use a Bias King Pro and a multimeter. A GT in the 4-7 range is safe for a lower bias on most EL34's and 6L6's, but a KT 66HP in the 6L6 bias setting draws 35ma. The 6L6 and EL34 may draw 17-26ma at a static -53 volts bias setting like the DR. When you have adjustable bias amps, as you decrease the negative voltage(Hotter) the tube tends to draw more current and you need to check your plate voltage and adjust the bias to meet your calculations for the tube type you are using and the % of MPD you want to run. In most cases, as you add more negative voltage, your plate volatge will decrease and you have to recalculate your math to obtain your preffered bias setings and % of MPD. Dont forget that each tube type has a maximum power dissipation and requires different bias settings base on the output of the tube. The 6L6 is 30 watts, EL34 is 25 watts etc. Once you do the math and playtest, you can tune your amp not just to reach a bias setting, but to sound the way you want it to. For instance, my SLO puts out 490 plate volts. I decided to put GT KT66HP's in for a 6L6 bottom end and an EL34 type top end. GT rates the KT66 as a 30 watt tube so I biased it at -45 Volts. The amp was flat, dull and the plates started to go red very quickly. I e-mailed Myles Rose at GT and he suggested that it is truly a 25 watt tube so I adjusted the bias after a few plate voltage readings to -38 volts. This was still a bit too hot on the plates and they started to glow orange after a few minutes. After another e-mail to Myles he said, run it at 65% MPD. At -34 Volts it was perfect. It had great bloom, tone and power. It his the sweet spot and was a lesson in how differnt tube types react to different bias setting regardless of the norm.

Study safety, use trial and error and ask people who know a hell of a lot more than you and you may stumble onto a proper way to bias an amp and that it is not necessary to run tubes according to a standard %.

 

[Guitarzan]

I use a Bias King Pro and a multimeter. A GT in the 4-7 range is safe for a lower bias on most EL34's and 6L6's, but a KT 66HP in the 6L6 bias setting draws 35ma. The 6L6 and EL34 may draw 17-26ma at a static -53 volts bias setting like the DR. When you have adjustable bias amps, as you decrease the negative voltage(Hotter) the tube tends to draw more current and you need to check your plate voltage and adjust the bias to meet your calculations for the tube type you are using and the % of MPD you want to run. In most cases, as you add more negative voltage, your plate volatge will decrease and you have to recalculate your math to obtain your preffered bias setings and % of MPD. Dont forget that each tube type has a maximum power dissipation and requires different bias settings base on the output of the tube. The 6L6 is 30 watts, EL34 is 25 watts etc. Once you do the math and playtest, you can tune your amp not just to reach a bias setting, but to sound the way you want it to. For instance, my SLO puts out 490 plate volts. I decided to put GT KT66HP's in for a 6L6 bottom end and an EL34 type top end. GT rates the KT66 as a 30 watt tube so I biased it at -45 Volts. The amp was flat, dull and the plates started to go red very quickly. I e-mailed Myles Rose at GT and he suggested that it is truly a 25 watt tube so I adjusted the bias after a few plate voltage readings to -38 volts. This was still a bit too hot on the plates and they started to glow orange after a few minutes. After another e-mail to Myles he said, run it at 65% MPD. At -34 Volts it was perfect. It had great bloom, tone and power. It his the sweet spot and was a lesson in how differnt tube types react to different bias setting regardless of the norm.

Study safety, use trial and error and ask people who know a hell of a lot more than you and you may stumble onto a proper way to bias an amp and that it is not necessary to run tubes according to a standard %.

Thank you for taking the time to write this! I greatly appreciate your knowledge!

 

[boogieslide]

This is great stuff. I have been toying with this lately as well.
I have one quad of EL34s, 4 different quads of 6L6s, and a pair of Mesa 6L6s that I am going to experiment with. I got through all but one quad of 6L6s with measuring and recording each set in my DR with every combination of options including 6L6 in EL34 mode. The measurements varied quite a bit.
I have not had a chance to tone test now to equate any tonal differences between these tubes, modes, and bias readings. So many options, such little time.
Off of what you are saying about ~35ma being best Boogiebabies.....I believe I had a quad of 6L6s that fell into that range when running EL34 mode with Tube/Spongy.
I am anxious to see what running at 50watts will do as well.

 

[Boogiebabies]

No problem bro. This is what this place is about. The Mesa brotherhood is strong.

There are also other ways to bias your amp, but this is how I do it. You can do more research and learn about the shunt method. Each method is open for debate, but this is the best way to get the job done. Also, you can get Bias meters that read the plate voltage as well so you dont have to poke around the power tube pins. I learned this the hard was at 490V and a blue flash, but after many years I feel comfortable with a multi meter and the bias King Pro. Most techs and Guru's also mention turning all of the knobs to 0 includeing the tone controls. I also made a rig to drain filter caps before I do any work. After you get the hang of it, you can also bias for the rise in current under load to get the power amp to compress the way you want it.
When your playing and playing loud, your bias readings may shoot upt to 80ma's. Theres a lot to fiddle with and try.Safety is paramount when learning to bias an amp.

The thing I like the most about Mesa amps is If I dont feel like messing around with the bias, I can pop any color set in and be safe. My personal color code is grey and white. They give you enough draw to not seem so grainy at lower volume.

Enjoy,

Ed

 

[Boogiebabies]

This is great stuff. I have been toying with this lately as well.
I have one quad of EL34s, 4 different quads of 6L6s, and a pair of Mesa 6L6s that I am going to experiment with. I got through all but one quad of 6L6s with measuring and recording each set in my DR with every combination of options including 6L6 in EL34 mode. The measurements varied quite a bit.
I have not had a chance to tone test now to equate any tonal differences between these tubes, modes, and bias readings. So many options, such little time.
Off of what you are saying about ~35ma being best Boogiebabies.....I believe I had a quad of 6L6s that fell into that range when running EL34 mode with Tube/Spongy.
I am anxious to see what running at 50watts will do as well.

After years of bias testing different tubes and ratings, it has really been expensive and a pain in the ***. In the end, I have a pretty good idea of what I can pop in and sound good within a safe range.

Regarding running a 100 watter at 50, the bias gets hotter because the two missing tubes are not there drawing plate voltage and negative volatge. It usually goes up around 5ma, but 50 watts is only 3 decibels less than 100 watts, but it should seem fatter and warmer. I like headroom so I never run at 50 watts. The only amp I run at 50 is my 2555 Silver Jubilee with the triode switch. It's a fat beast, but the headroom is gone. The 100 watt pentode mode needs to be above 6 to get rid of the grainy Mashall fizz and it is ungodly loud.

 

[boogieslide]

This is great stuff. I have been toying with this lately as well.
I have one quad of EL34s, 4 different quads of 6L6s, and a pair of Mesa 6L6s that I am going to experiment with. I got through all but one quad of 6L6s with measuring and recording each set in my DR with every combination of options including 6L6 in EL34 mode. The measurements varied quite a bit.
I have not had a chance to tone test now to equate any tonal differences between these tubes, modes, and bias readings. So many options, such little time.
Off of what you are saying about ~35ma being best Boogiebabies.....I believe I had a quad of 6L6s that fell into that range when running EL34 mode with Tube/Spongy.
I am anxious to see what running at 50watts will do as well.

After years of bias testing different tubes and ratings, it has really been expensive and a pain in the ***. In the end, I have a pretty good idea of what I can pop in and sound good within a safe range.

Regarding running a 100 watter at 50, the bias gets hotter because the two missing tubes are not there drawing plate voltage and negative volatge. It usually goes up around 5ma, but 50 watts is only 3 decibels less than 100 watts, but it should seem fatter and warmer. I like headroom so I never run at 50 watts. The only amp I run at 50 is my 2555 Silver Jubilee with the triode switch. It's a fat beast, but the headroom is gone. The 100 watt pentode mode needs to be above 6 to get rid of the grainy Mashall fizz and it is ungodly loud.

I noticed that my readings were the highest with the pair and running at 50watts. I really just want to try it because I can Plus I somehow lost one of the 4 Mesa tubes I had so I figured I would give a pair a try while I am experimenting. I ran my Tverb in 50watt mode and really didn't find much difference. Actually it seemed to take away a little thump. The DRs seem to have more low end though so that might not be a bad or missed thing. I know volume is not a noticeable difference, but I do want to see how the tone is effected.

 

[Boogiebabies]

You should be just fine running it at 50 watts. Your findings are right on the money.

 

[Kung-Fool]

Awesome info boogiebabies. Thanks.