Roadster with =C= 6L6 tubes on EL34 bias

[Storm]

Hi people,

I did a quick search but didn't yield anything. It is safe to run the SED 6L6 tubes with the Roadster's bias switch set to EL34 mode? I tried it and nothing has gone bust yet and it sounds a lot warmer (good!). The tubes do get a blue band around the outside of them, so I'm a bit concerned if it is safe to do.

Ciao ...

 

[S.C.I.E.N.C.E.]

My guess is no

You are going to blow a tube...or 4

They use different voltages

Its like putting diesel in a unleaded fuel car
It might run for a little while, but it will mess things up....big time

 

[redhouse]

Hello.

Put a Trimpot, then you can run your Mesa Hot and safety.

Abraço

 

[Storm]

No worries guys, I guess for the time being I'll play it safe and stick with 6L6 mode. Better safe than sorry.

Ciao ...

 

[MusicManJP6]

No worries guys, I guess for the time being I'll play it safe and stick with 6L6 mode. Better safe than sorry.

Ciao ...

That's the best idea man...

 

[Core9]

Use a bias meter to check the current draw. If it's in a safe range it will do just fine. I'm currently running my DR with Mesa ST430 (I think that is the correct tube number, I could be wrong though) 6L6's in EL34 mode and they are doing fine. Mesa's 6L6 mode is biased very cold. Start out in Spongy and Tube Rec modes. As long as the plates are not glowing red you should be fine, but a current draw reading will tell you for sure. Just have the amp in a dark room and look for any kind of a red glow coming from the main tube plates themselves while playing the amp. My bias current got a little higher than I like when using Bold and Silicon Rec mode with no redness showing up in the plates. I found Bold & Tube Rec does really well for my tubes, got them very close to perfect. I run my amp in Tube Rec and Spongy most of the time, but these settings still keep the 6L6's somewhat on the cold side. Amp is doing fine and sounds great.

 

[domct203]

Use a bias meter to check the current draw. If it's in a safe range it will do just fine. I'm currently running my DR with Mesa ST430 (I think that is the correct tube number, I could be wrong though) 6L6's in EL34 mode and they are doing fine. Mesa's 6L6 mode is biased very cold. Start out in Spongy and Tube Rec modes. As long as the plates are not glowing red you should be fine, but a current draw reading will tell you for sure. Just have the amp in a dark room and look for any kind of a red glow coming from the main tube plates themselves while playing the amp. My bias current got a little higher than I like when using Bold and Silicon Rec mode with no redness showing up in the plates. I found Bold & Tube Rec does really well for my tubes, got them very close to perfect. I run my amp in Tube Rec and Spongy most of the time, but these settings still keep the 6L6's somewhat on the cold side. Amp is doing fine and sounds great.

+1

Stop the guesswork and get a bias probe. You can "adjust" your bias by using different grades of tubes. I've got SED =C= 6L6's from Doug running in 6L6 mode that draw 30-32 mA. (vs. 25-27mA for the stock STR-440 GRN) in my Roadster and I love them. If I wanted to I could get a "hotter" grade and get the amp to 35-38 mA., no amp "bias pot mod" needed. With a "colder" grade of 6L6 you can run in EL34 mode.

And as mentioned before, with all the power options (Bold/Spongy ; Tube Rec./Diode ; 6L6/EL34 bias) you can really tweak the power amp as-is, and with a bias probe and some education you can protect your $2K Mesa

Dom

 

[nomad100hd]

i'd never try it without a bias probe, the bias mod would be awesome as well.

 

[Storm]

I bought my SEDs from Doug and written on the box is 19.0mA. I'll just stick with the setup I have now, it's not like it sounds bad or anything. Thanks for the info anyway!

Ciao ...

 

[zeppelin]

So who knows where to find the bias mod for a Roadster/Roadking?

 

[redhouse]

So who knows where to find the bias mod for a Roadster/Roadking?

Why?

Leave it to a amp Tech.

I pay 50 € and now I can put all the valves I want.

By the way, I have a Single recto.

Abraço

 

[nomad100hd]

i'd like to find the bias mod for my nomad HD. I could probably figure it out but i'd like to see if someone else has done it.

If you can use a soldering iron, multimeter, can read schematics, and know how to discharge an amp there is no reason to have a tech do it! I'll keep my money and make a few bucks off of someone else who can't.

 

[zeppelin]

So who knows where to find the bias mod for a Roadster/Roadking?

Why?

Leave it to a amp Tech.

I pay 50 € and now I can put all the valves I want.

By the way, I have a Single recto.

Abraço

I build amps so I guess I am a tech. It would be nice to get a schematic or pics of the mod instead of tracing it out.

 

[nomad100hd]

I totally agree a pic is worth a lot!

 

[zeppelin]

Currently I am into other projects but when I get some time I will trace the circuit out and perform the mod if no one can help providing pics or schematics, and yes pics really do help. I recently re-tubed my Roadster with =C= 6L6's and while it does sound alot better to me I think if the bias could be adjusted it would warm it up.

 

[zeppelin]

Sorry, not to hijack this thread, got a little off topic but I wouldn't run any amp with the switch in the wrong setting, your asking for it. When running 6L6's have the switch set for 6L6 or when running EL34's set the switch to EL34. You may get away with it for a while but eventually something will breakdown and go bad, tubes, output xfmr, resistors, etc........... Why risk it.

 

[Core9]

Sorry, not to hijack this thread, got a little off topic but I wouldn't run any amp with the switch in the wrong setting, your asking for it. When running 6L6's have the switch set for 6L6 or when running EL34's set the switch to EL34. You may get away with it for a while but eventually something will breakdown and go bad, tubes, output xfmr, resistors, etc........... Why risk it.

Actually running 6L6 tubes on the EL34 setting is easier on the amp than running EL34 tubes on the EL34 setting. :wink:

Tube pin out is the same. The main difference between the tubes is idle current draw (i.e. the bias current). EL34 tubes require a higher bias setting than 6L6 tubes. When switching to the EL34 mode, the bias resister allows more current to flow. Since Mesa tubes are on the cold side of the spectrum, using the EL34 setting warms up the 6L6 tubes and gets them closer to the proper bias range. This will not harm an amp set up for EL34 tubes. Now on an amp that is set up for 6L6 tubes only, there is the possibility of burning the screen/grid resister because of the higher current draw when using EL34 tubes.

 

[nomad100hd]

I believe EL34 can handle higher voltages than 6L6's. One thing i noticed on my nomad schematic is when switching to EL34 mode the resistor dropping the screen grid voltage is bypassed. I'm not sure what real world difference that makes but it has the possibility to increase pa noise.

 

[212Mavguy]

From my experience in both user fixed bias and cathode bias amps that take both 6l6 and el34 types I have learned that a setting for 6l6 will be too cold for el34. Conversely, if I bias my amp to goose the el34 into the range it belongs and then stick in a 6l6, 6l6 runs too hot. That's in a hot running class A single ended type modded Fender Champ that runs tubes right at the edge of what they can handle long term current wise. It has a bias trim pot and a switch to use that pot or take it out of the circuit and use the stock cathode bias. So I use the stock bias for 6v6 and 6l6, use the bias trim for el34 and 6550. I also have a boutique Bluesbreaker with bias trim and balance pots, and I after have set the trim pot to el34 it needs to be backed down using 6l6's to keep from running them too hot.

If you wanted to see how the 6l6's of yours behave in your Mesa amp at el34 settings, turn it on in a dark room and then watch the plates of the tubes. If after five-ten minutes there is no redplating then you are probably OK. I do agree with the posts saying to get a bias meter, one that handles a pair of sockets at a time is preferable. If there is a lower voltage switch setting on the amp then use it for the 6l6's. May or may not work.

The only reason that I think that it might work is that the Mesa Amps tend to be biased into a relatively cold class AB. A cold el34 AB bias setting might run those 6l6's right into a hotter class A bias, and that will warm up the tone nicely.

Best is to use the tubes with their respective switch settings and get tubes in the proper ranges for your Mesa amp, or better yet, get a bias trim pot installed.

 

[zeppelin]

Best is to use the tubes with their respective switch settings and get tubes in the proper ranges for your Mesa amp, or better yet, get a bias trim pot installed.[/quote]

+1