Modern Classic ( Bias)

I noticed both of mine were drawing 40 plus MA per tube and that seems a little excessive and mushy. I dailed it back to 30-32ma of current draw per tube and it tightened up the bottom... sounded better to me. I have no idea what the plate voltage is on these things.. anyone? I just use a bias probe and adjust by ear.
 
lespaul6":1wclshk5 said:
I noticed both of mine were drawing 40 plus MA per tube and that seems a little excessive and mushy. I dailed it back to 30-32ma of current draw per tube and it tightened up the bottom... sounded better to me. I have no idea what the plate voltage is on these things.. anyone? I just use a bias probe and adjust by ear.
Click to expand...

Thanks for the help. I will be using a compubias so I will be mainly looking at IK and wattage. I think IK is mA. IP plate voltage maybe? I guess mainly the end result is the wattage reading. Its a little different way of biasing but it seemed like the safest to me and fastest. I have yet to get to it I wanted to see what others have been doing, or been told to bias at. I will most likely take a reading of the current bias reading before changing them out, but even then they could have drifted by now.
 
I was able to catch the plate voltage of another modern classic on a different forum... seems they are around the 500 mark. With that being the case I think my chart says that 4 el34's at 100 watts should be 28ma to 34ma not too exceed by too much more for the sake of tube life and headroom etc. I play my amps loud anyway so I dont do the underbias play in the bedroom thingy.
 
I have heard that claim, however, I'm not sure if it is true? anyway, I have el34L in there right now biased at about 30-32 ma of current draw and they sound good.. much better than they did at 48! you should try out different settings and see what you like the best. report back

here is a link to a bias calculator: http://www.webervst.com/tubes1/calcbias.htm

as you can see an el34 with a 500 plate voltage = 35ma but that is at 70 percent.. I normally use 50 percent because when you turn up the amp you turn up the current draw etc. better tube life overall... been using this method for years with good results.
 
I dont know.. for marshall's there is a conversion of parts needed, various resistors and bias supply stuff etc... its not a bias and go thing for a marshall anyway.
 
wheelman":2fhf1w9l said:
lespaul6":2fhf1w9l said:
I noticed both of mine were drawing 40 plus MA per tube and that seems a little excessive and mushy. I dailed it back to 30-32ma of current draw per tube and it tightened up the bottom... sounded better to me. I have no idea what the plate voltage is on these things.. anyone? I just use a bias probe and adjust by ear.
Click to expand...

Thanks for the help. I will be using a compubias so I will be mainly looking at IK and wattage. I think IK is mA. IP plate voltage maybe? I guess mainly the end result is the wattage reading. Its a little different way of biasing but it seemed like the safest to me and fastest. I have yet to get to it I wanted to see what others have been doing, or been told to bias at. I will most likely take a reading of the current bias reading before changing them out, but even then they could have drifted by now.
Click to expand...


wheelman... what were the readings on your compu bias? And what were your final readings in order to achieve the proper wattage (25watts).
 
lespaul6":1aiufwxo said:
wheelman":1aiufwxo said:
lespaul6":1aiufwxo said:
I noticed both of mine were drawing 40 plus MA per tube and that seems a little excessive and mushy. I dailed it back to 30-32ma of current draw per tube and it tightened up the bottom... sounded better to me. I have no idea what the plate voltage is on these things.. anyone? I just use a bias probe and adjust by ear.
Click to expand...

Thanks for the help. I will be using a compubias so I will be mainly looking at IK and wattage. I think IK is mA. IP plate voltage maybe? I guess mainly the end result is the wattage reading. Its a little different way of biasing but it seemed like the safest to me and fastest. I have yet to get to it I wanted to see what others have been doing, or been told to bias at. I will most likely take a reading of the current bias reading before changing them out, but even then they could have drifted by now.
Click to expand...


wheelman... what were the readings on your compu bias? And what were your final readings in order to achieve the proper wattage (25watts).
Click to expand...


I didn't get to yet I got another amp that needs attention first. Hopefully I can get to it soon. I will probably shoot for around 15-16 watts.
 
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