I installed el34's in my lonestar v1. Upon playing it for a couple of minutes I noticed that when I played at very low volume, the amp distorted. As I increased the volume the distortion disappeared. I then realized I had forgotten to switch the bias select switch. I turned off the amp and switched it over, but had the same result. Swapped my 6L6's back in (and remembered to switch bias this time) and had the same distortion. Now I'm afraid I've damaged the amp. I've had resisters blow in past tube amps, but did not notice any smell or catastrophic failure this time. I am hoping it is just a coincidence and something else may be the problem, but I don't know. Anyone have any ideas?
Forgot to switch bias switch... did I damage the amp?
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Charles Reeder
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Hey!
I can't tell your for sure whether you have already damaged your amp...but I can tell you why the potential might possibly be there.
It's because of the 'filament-tube-voltage'. The filament tube on a 6L6, 6V6 etc. draws approx. 6-volts. An EL34/6CA7; draws approx. 12 volts.
When attempting to run an EL34 type tube on 6-volts; the filament can't draw the required voltage; thus straining (over-heating) the transformer.
It is actually O.K. to run a 6L6 (or variants )on the EL34 setting which has the potential for supplying 12-volts; as the 6L6 type tube will only draw what is needed.
The bias for the two (should be) set differently; but if a 6L6 or 6V6 etc. is used on the EL34 setting; one could take a bias-reading and if the bias didn't exceed safe limits; it could be run in the EL34 setting.
The opposite IS NOT TRUE. If (and I'm making a dangerous assumption here) Mesa has designed the BIAS-SWITCH; so that it offers up 6-volts set on 6L6; and 12-volts set on EL34; than the use of EL34's (on the 6L6 setting) can most certainly damage the amp. IF HOWEVER; they designed the amp to run both 6L6's AND EL34's at 12-volts then the only damaged likely to occur would be the result of tubes running entirely too hot; which might burn some resistors. But, you said you didn't see or smell smoke.
You need to find out from someone who can read circuits; if the Lonestar bias-switch does toggle between 6 and 12 volts; to know more.
Would someone with the knowledge; please weigh in?
Best of luck! Charles
I can't tell your for sure whether you have already damaged your amp...but I can tell you why the potential might possibly be there.
It's because of the 'filament-tube-voltage'. The filament tube on a 6L6, 6V6 etc. draws approx. 6-volts. An EL34/6CA7; draws approx. 12 volts.
When attempting to run an EL34 type tube on 6-volts; the filament can't draw the required voltage; thus straining (over-heating) the transformer.
It is actually O.K. to run a 6L6 (or variants )on the EL34 setting which has the potential for supplying 12-volts; as the 6L6 type tube will only draw what is needed.
The bias for the two (should be) set differently; but if a 6L6 or 6V6 etc. is used on the EL34 setting; one could take a bias-reading and if the bias didn't exceed safe limits; it could be run in the EL34 setting.
The opposite IS NOT TRUE. If (and I'm making a dangerous assumption here) Mesa has designed the BIAS-SWITCH; so that it offers up 6-volts set on 6L6; and 12-volts set on EL34; than the use of EL34's (on the 6L6 setting) can most certainly damage the amp. IF HOWEVER; they designed the amp to run both 6L6's AND EL34's at 12-volts then the only damaged likely to occur would be the result of tubes running entirely too hot; which might burn some resistors. But, you said you didn't see or smell smoke.
You need to find out from someone who can read circuits; if the Lonestar bias-switch does toggle between 6 and 12 volts; to know more.
Would someone with the knowledge; please weigh in?
Best of luck! Charles
Both 6L6 tubes and EL34 tubes run the same 6 volt heater voltage. The EL34 heater does need a bit more current, 1.4 amp vs .9, but that will not have any bearing.
What does need to change though is the fixed bias voltage. The bias voltage sets the operating current of the output tubes.
If you run a 6L6 tube with the bias set to EL34 spec it will run very hot and eventually fail due to the heat (Could be minutes or hours). The tell tail sign is that the anode (which is most of what you can see internally in the tube) will become red with the heat. An EL34 tube run with the 6L6 bias setting will run cold and sound (probably at higher volume) bad without causing damage.
Since El34 tubes were run with the 6L6 bias I would expect that your amp is fine and would be looking at the preamp tubes as the cause of your problem.
Hope that helps shed some light
What does need to change though is the fixed bias voltage. The bias voltage sets the operating current of the output tubes.
If you run a 6L6 tube with the bias set to EL34 spec it will run very hot and eventually fail due to the heat (Could be minutes or hours). The tell tail sign is that the anode (which is most of what you can see internally in the tube) will become red with the heat. An EL34 tube run with the 6L6 bias setting will run cold and sound (probably at higher volume) bad without causing damage.
Since El34 tubes were run with the 6L6 bias I would expect that your amp is fine and would be looking at the preamp tubes as the cause of your problem.
Hope that helps shed some light
Charles Reeder
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J.J....
It appears that I am wrong about the 6-volt/12-volt matter. If nothing else; I guess it at least confirms my assertions that I AM NOT A TECHIE!
I was told this info by someone who seemed to me to be in a position to know; but alas; apparently not.
At any rate; it actually makes me breatehe a sigh of relief. I knew the bias settings could be a cause for tube failure if toggling between them; and kept a constant eye out for bias readings. Now I have less to worry about...and it opens up the possibility of trying out 6L6-ONLY amps with EL34's (with the necessary bias adjustments of course)!
Thanks for weighing in with your input and correction.
Cheers: Charles
It appears that I am wrong about the 6-volt/12-volt matter. If nothing else; I guess it at least confirms my assertions that I AM NOT A TECHIE!
I was told this info by someone who seemed to me to be in a position to know; but alas; apparently not.
At any rate; it actually makes me breatehe a sigh of relief. I knew the bias settings could be a cause for tube failure if toggling between them; and kept a constant eye out for bias readings. Now I have less to worry about...and it opens up the possibility of trying out 6L6-ONLY amps with EL34's (with the necessary bias adjustments of course)!
Thanks for weighing in with your input and correction.
Cheers: Charles
Charles, there is a lot of bad information around in regards to tube amps. I'm always happy when I can help to sort some of it out.
I looked at the Lonestar V1 schematic which is available around the net and it does show that the filament connections do not change when switching the EL34/6L6 bias switch.
In regards to trying El34 tubes in 6L6 only amps, you would almost certainly need to modify the bias circuit as the normal adjustment range would probably not cover what an EL34 needs. The LSC schematic shows that the bias voltage is -38V for El34 and -51 for 6L6. That is all that changes with the bias switch. KT-66 could also be an option.
You would really need to look at an output tube swap on an amp by amp basis as there are a number of other areas that should be checked such as screen voltages and resistors. A good amp tech would be able to do that. In general, an El34 can take anything that a 6L6 will.
Cheers,
Jason.
I looked at the Lonestar V1 schematic which is available around the net and it does show that the filament connections do not change when switching the EL34/6L6 bias switch.
In regards to trying El34 tubes in 6L6 only amps, you would almost certainly need to modify the bias circuit as the normal adjustment range would probably not cover what an EL34 needs. The LSC schematic shows that the bias voltage is -38V for El34 and -51 for 6L6. That is all that changes with the bias switch. KT-66 could also be an option.
You would really need to look at an output tube swap on an amp by amp basis as there are a number of other areas that should be checked such as screen voltages and resistors. A good amp tech would be able to do that. In general, an El34 can take anything that a 6L6 will.
Cheers,
Jason.
I just joined the Electra Dyne party as of last night ! I am bringing this thread back to the top as it relates the issue I discovered when I got the amp home. The bias switch was set to EL34 but the am has 6L6's in it. When I bought the amp I played it for maybe 20 minutes that way. On top of that one of the 6L6's had actually fallen out and was laying broken on the bottom of the combo. It sounded really good when I played it and the seller was motivated to sell so based on the deal I got I went ahead and bought it.
I didn't smell anything getting overly hot - but my question is what long term damage could be done? I should have given it the once over before playing it but it was one of those situations where the guy had the amp all ready to be played with guitar plugged in when I got there- still no excuses on my end.
I have two follow up questions.
As I only have 3 tubes at the moment, which tube would I pull out - or need to have in place - to run at 45watts?
If I don't go with Boogie tubes, what do I need to look for in values in a 6L6. I've not been down this road before with non-bias amps.
Even despite the above, the amp sounds really good. Like a 2x12 combo in a 1x12 ( 27" model ).
Thanks for any help/advice/opinions !!
I didn't smell anything getting overly hot - but my question is what long term damage could be done? I should have given it the once over before playing it but it was one of those situations where the guy had the amp all ready to be played with guitar plugged in when I got there- still no excuses on my end.
I have two follow up questions.
As I only have 3 tubes at the moment, which tube would I pull out - or need to have in place - to run at 45watts?
If I don't go with Boogie tubes, what do I need to look for in values in a 6L6. I've not been down this road before with non-bias amps.
Even despite the above, the amp sounds really good. Like a 2x12 combo in a 1x12 ( 27" model ).
Thanks for any help/advice/opinions !!
screamingdaisy
Well-known member
So far as I know the bias mismatch is harder on the tubes than the amp.
In 45w mode only the middle pair are on.
If you go with non-Boogie tubes you need to indicate to the vendor that you need them in the correct range for a Mesa and they need to provide the right range. For this reason I recommend sticking to reputable tube vendors that actually own their own test equipment.
In 45w mode only the middle pair are on.
If you go with non-Boogie tubes you need to indicate to the vendor that you need them in the correct range for a Mesa and they need to provide the right range. For this reason I recommend sticking to reputable tube vendors that actually own their own test equipment.
