EL34 bias....525V

[jkdsteve]

Where would you bias these...have a pair of SED EL34s and get conflicting opinions on bias.

PV=525, I have them at 32......was biasing EL34s around 37-39 before I was told this was probably too hot :-/

 

[MrDan666]

Where would you bias these...have a pair of SED EL34s and get conflicting opinions on bias.

PV=525, I have them at 32......was biasing EL34s around 37-39 before I was told this was probably too hot :-/

Which amp are you using them with?

With a PV of 525vdc and biasing to 70% dissipation, you would bias to approx 33-34mA. But if you prefer the tone with them biased at 37mA then that should be fine with Winged C EL34's. I have never had any problems biasing them hotter than 70% and know plenty of other techs who bias them hotter than 70% too.

Here's a link to the Weber Bias Calculator, which you can use in future for reference
http://www.webervst.com/tubes1/calcbias.htm

 

[skoora]

My metro plexi has about 490 on the plates and I've been running my hottest EL34 at 25 which was recommended by two guys I respect a lot in Seattle. It seemed low to me, if you go by common theories but the amp sounds amazing and I've had awesome longevity from running them a little cooler. I found if I ran them at 30 or higher I would pop the HT fuse. I think as long as the tube is out of crossover distortion (real cold) it's slim degrees of tonal difference. This of course could change I guess depending on the circuit. I know enough to hurt myself

 

[hellaboogie]

Where would you bias these...have a pair of SED EL34s and get conflicting opinions on bias.

PV=525, I have them at 32......was biasing EL34s around 37-39 before I was told this was probably too hot :-/

Try using this http://www.webervst.com/tubes1/calcbias.htm

 

[glpg80]

My metro plexi has about 490 on the plates and I've been running my hottest EL34 at 25 which was recommended by two guys I respect a lot in Seattle. It seemed low to me, if you go by common theories but the amp sounds amazing and I've had awesome longevity from running them a little cooler. I found if I ran them at 30 or higher I would pop the HT fuse. I think as long as the tube is out of crossover distortion (real cold) it's slim degrees of tonal difference. This of course could change I guess depending on the circuit. I know enough to hurt myself

you're backwards on your tube theory. you bias hotter to get out of crossover distortion for class A/B PP, not colder.

 

[kirk]

its easy math bro...25watts(el34's are rated at)divided by plate voltage(your case=525) take that answer multiply it by .7(70%) =your bias ,.. your is 25/525=.04761905x.7=.033333 or 33ma's must be a marshall and if it is you have to use wing c's anything else WILL fail el 34's have a screen voltage rating of 475,most marshalls go over that and the wing c's can take that abuse,i havent found another brand or tube that can take that for too long

 

[MississippiMetal]

It truly depends on what style of music you're playing as to whether or not you wanna bias them at 70% or above. If you're playing anything that requires tight lowend and topend clarity, I'd shoot for 60-63%, no more than 66%. 70% and above generally means farty lowend and overall mushier tone.

Also, you can't bias AB PP amps out of crossover distortion. You can make the crossover distortion basically inaudible, but the crossover notch still exists. The only way to completely remove crossover distortion is to run the amp in pure Class A. Even then, the even order harmonics that so many people are fond of in Class A SE amps are canceled out in a push-pull arrangement, so there is really no point. Top that off with the fact that to get the output section into Class A operation, you'd have to bias the grid so hot that the tubes would overdissipate with the quickness, unless you're down for modding the amp to drop the plate voltage considerably.

 

[skoora]

My metro plexi has about 490 on the plates and I've been running my hottest EL34 at 25 which was recommended by two guys I respect a lot in Seattle. It seemed low to me, if you go by common theories but the amp sounds amazing and I've had awesome longevity from running them a little cooler. I found if I ran them at 30 or higher I would pop the HT fuse. I think as long as the tube is out of crossover distortion (real cold) it's slim degrees of tonal difference. This of course could change I guess depending on the circuit. I know enough to hurt myself

you're backwards on your tube theory. you bias hotter to get out of crossover distortion for class A/B PP, not colder.

it was just my phrasing. I was meaning your real cold if your in audible crossover distortion.

 

[glpg80]

My metro plexi has about 490 on the plates and I've been running my hottest EL34 at 25 which was recommended by two guys I respect a lot in Seattle. It seemed low to me, if you go by common theories but the amp sounds amazing and I've had awesome longevity from running them a little cooler. I found if I ran them at 30 or higher I would pop the HT fuse. I think as long as the tube is out of crossover distortion (real cold) it's slim degrees of tonal difference. This of course could change I guess depending on the circuit. I know enough to hurt myself

you're backwards on your tube theory. you bias hotter to get out of crossover distortion for class A/B PP, not colder.

it was just my phrasing. I was meaning your real cold if your in audible crossover distortion.

do know that crossover distortion is hard to tell with your own ears - it is not something you can easily pick out in itself. you could pull the tone card and say you can hear the difference, but an oscilloscope is best for removing crossover.

thats why i dislike the 70% "rule" and also why i do not use a bias probe for amplifiers. for Class A/BPP O-scope method and a signal generator is my recommended/preferred method, or using the transformer shunt method. also all tubes (and amplifiers for that matter) are not the same - datasheet values will give you a ballpark guideline but you can deviate above and below except for absolute max numbers.

there are others like psychodave who prefer to set their bias level using their ears, and then testing to make sure it is within datasheet specs of the tubes used. this method is also something you could do using a voltmeter or bias probes - depends on how well you trust your ears and the volumes you are playing at as well as the speaker sensitivity.

 

[glpg80]

It truly depends on what style of music you're playing as to whether or not you wanna bias them at 70% or above. If you're playing anything that requires tight lowend and topend clarity, I'd shoot for 60-63%, no more than 66%. 70% and above generally means farty lowend and overall mushier tone.

Also, you can't bias AB PP amps out of crossover distortion. You can make the crossover distortion basically inaudible, but the crossover notch still exists. The only way to completely remove crossover distortion is to run the amp in pure Class A.

then please explain what the class A in class A/B stands for? you can adjust the crossover distortion out of the output signals. whoever told you otherwise is wrong, or whatever text you researched that said otherwise is incorrect. you are adjusting the positive and negative sin wave zero crossing alterations and the period of time between those alterations - you CAN eliminate it all together and it is souly based on the bias sweep available in the amplifier.

the correct answer is you cannot bias it completely out of an amplifier using anything else but an oscilloscope without losing efficiency. you are getting class A/B and class B confused with one another.

what cancels in class A/B bias is not harmonics, what cancels in class A/B push pull is the noise factor from the AC ripple riding on the DC voltage from the power supply filtering - depending on the filter design of the amplifier basically the diode noise and any lead interference is what is canceled. harmonics are always present and compared to class A bias you will still have a harmonic content in the 3-5% range which is why class A/B is so popular - noise filter control, stability, possible efficiency, and signal integrity. the only downside is heat production which is why class D amplifiers are now more commonly used in the workfield where music is not concerned.

 

[MississippiMetal]

It truly depends on what style of music you're playing as to whether or not you wanna bias them at 70% or above. If you're playing anything that requires tight lowend and topend clarity, I'd shoot for 60-63%, no more than 66%. 70% and above generally means farty lowend and overall mushier tone.

Also, you can't bias AB PP amps out of crossover distortion. You can make the crossover distortion basically inaudible, but the crossover notch still exists. The only way to completely remove crossover distortion is to run the amp in pure Class A.

then please explain what the class A in class A/B stands for? you can adjust the crossover distortion out of the output signals. you are adjusting the positive and negative sin wave zero crossing alterations and the period of time between those alterations - you CAN eliminate it all together and it is souly based on the bias sweep available in the amplifier.

the correct answer is you cannot bias it completely out of an amplifier using anything else but an oscilloscope without losing efficiency. you are getting class A/B and class B confused with one another.

what cancels in class A/B bias is not harmonics, what cancels in class A/B push pull is the noise factor from not using switch mode power supply filtering - depending on the filter design of the amplifier the diode noise and interference is what is canceled. harmonics are always present and compared to class A bias you will still have a harmonic content in the 3-5% range.

Class A is defined as when a valve or valves is/are biased so that current flows for the entire input cycle.

While it's true that the crossover notch can be minimized to a degree where it's basically unnoticeable on an oscilloscope, this has to be done with lower plate voltages. I honestly don't think it's possible to take 525V and bias EL34's completely out of visible crossover distortion without redplating the valves. I'll gladly retract my statement if I can witness it.

Even order harmonics generated within the class A output are indeed cancelled if it is in a push-pull configuration. Only even order harmonics generated in the preamp stages are amplified. This is due to the PP stage being a differential amplifier.

I think you should check out Aiken's article on crossover notch biasing, which you said you prefer.

http://www.aikenamps.com/CrossoverNotchBiasing.html


All that being said, I don't think biasing needs to be as precise a process as many have made it. Keep your idle dissipation within safe limits, and tweak to tonal preference.

 

[glpg80]

It truly depends on what style of music you're playing as to whether or not you wanna bias them at 70% or above. If you're playing anything that requires tight lowend and topend clarity, I'd shoot for 60-63%, no more than 66%. 70% and above generally means farty lowend and overall mushier tone.

Also, you can't bias AB PP amps out of crossover distortion. You can make the crossover distortion basically inaudible, but the crossover notch still exists. The only way to completely remove crossover distortion is to run the amp in pure Class A.

then please explain what the class A in class A/B stands for? you can adjust the crossover distortion out of the output signals. you are adjusting the positive and negative sin wave zero crossing alterations and the period of time between those alterations - you CAN eliminate it all together and it is souly based on the bias sweep available in the amplifier.

the correct answer is you cannot bias it completely out of an amplifier using anything else but an oscilloscope without losing efficiency. you are getting class A/B and class B confused with one another.

what cancels in class A/B bias is not harmonics, what cancels in class A/B push pull is the noise factor from not using switch mode power supply filtering - depending on the filter design of the amplifier the diode noise and interference is what is canceled. harmonics are always present and compared to class A bias you will still have a harmonic content in the 3-5% range.

Class A is defined as when a valve or valves is/are biased so that current flows for the entire input cycle.

While it's true that the crossover notch can be minimized to a degree where it's basically unnoticeable on an oscilloscope, this has to be done with lower plate voltages. I honestly don't think it's possible to take 525V and bias EL34's completely out of visible crossover distortion without redplating the valves. I'll gladly retract my statement if I can witness it.

Even order harmonics generated within the class A output are indeed cancelled if it is in a push-pull configuration. Only even order harmonics generated in the preamp stages are amplified. This is due to the PP stage being a differential amplifier.

I think you should check out Aiken's article on crossover notch biasing, which you said you prefer.

http://www.aikenamps.com/CrossoverNotchBiasing.html

All that being said, I don't think biasing needs to be as precise a process as many have made it. Keep your idle dissipation within safe limits, and tweak to tonal preference.

ill try to tackle this using your textbook scenario - versus a real world scenario.

explain when power tubes are biased class A/B the limitations of harmonic canceling of differential amplifiers? in a perfect scenario yes, but this is not the case. i was talking about actual factual content based on real world scenarios - ripple content in most amplifiers is below 6% which in tolerances for class A/B anything up to 20% is acceptable.

A good bit of even order harmonic canceling on Class A/B amps comes from the quality of the tubes and the method of bias which here is class A/BPP - in a perfect world, you will have even order harmonics. moreseo as tubes drift with age.

if you expect to cancel all even harmonics but refuse to believe you have the ability to never bias outside the realms of statistical vs analytical and/or apply realistic tube qualities, you admit that the even harmonics will exist in the power supply section regardless

the reason why is because the sin of the input does not appear in the even harmonics - it is always raised to the power of an even number (pairs - positive/negative alerations) and in an ideal setting, the two outputs cancel even harmonics assuming perfect matching. however, we all know that is physically impossible - not every tube is exactly the same, approximately the same yes, but exact no. thus when the two outputs are subtracted (differential output) the even harmonics on both sides will cancel by textbook meanings - in real world you will have even order harmonic content.

the only thing that cancels that i have ever known of with no other variables is power supply switching noise at your output blocked also by the fact your OT acts like a low pass filter. the the only additional place this does not apply is in switch mode power supplies where ripple is much less if any of a problem (very high frequency)

 

[glpg80]

While it's true that the crossover notch can be minimized to a degree where it's basically unnoticeable on an oscilloscope, this has to be done with lower plate voltages. I honestly don't think it's possible to take 525V and bias EL34's completely out of visible crossover distortion without redplating the valves. I'll gladly retract my statement if I can witness it.

crossover is at a much lower point than you expect. the point at which this is met is easy to define using a calibrated oscilloscope. just outside of crossover is where tubes belong as far as bias goes. you bias in a realm using the o-scope where compression does not apply.

one thing many people get wrong is using a transducer as a load when biasing. this is wrong - a resistive load rated at 250W (minimum 55W) should be used across the OT. this will give you the exact constant you need to successfully notch bias an amplifier using a signal generator and an o-scope. i have done it for years and it is much quicker and much more reliable IMHO.

i used to use the transformer shunt method but have cleared away from it as you are shooting in the wind as far as crossover distortion is concerned with class A/BPP. the only method that can deter this are the guys using their ears.