The right way to bias with bias current checkers?

Nightburst

Nightburst

New member
Hope some guys here can help me with adjusting the bias on my Bogner Ecstasy correctly, I got all the tools and tubes I need but not the knowledge of how to do it.
This is what I got now:

4 x bias current checker
4x E34L JJ tubes
1x multimeter set to 200mA area

I took the chassis out and noticed there's only one bias trim pot.

Somebody eles uses the bias current checker method? Please enlighten me on how to do it, it shouldn't be that difficult!?
 
Re: The right way to bias with bias current checkers?

Thanks, I found out that setting the meter on volts gives me the amps reading (got it from the bias rite site).
All tubes read around 39 but one is around 16!? Tried in different sockets, it's probably a bad tube.
The bias pot can't be adjusted lower anymore. Is 39ma safe to operate on in this amp?

I think the generic 'right' bias current level is around 35ma, but I know guys here like to bias the tubes a little hotter for better tone.
 
Re: The right way to bias with bias current checkers?

The proper way to bias starts with plate voltage.

If your bias tool is the Bias Rite it should give you the option of measuring your plate voltage. If you get me that plate voltage I can take you through the steps.

PS. Hotter doesn't necessarily mean the amp will sound better, but it does mean the tubes will wear faster.
 
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Re: The right way to bias with bias current checkers?

wixedmords said:
The proper way to bias starts with plate voltage.

If your bias tool is the Bias Rite it should give you the option of measuring your plate voltage. If you get me that plate voltage I can take you through the steps.

PS. Hotter doesn't necessarily mean the amp will sound better, but it does mean the tubes will wear faster.
Click to expand...

Thanks for helping! I don't have the bias rite, I got these made by a tech so I can use them with a multimeter. Where do I measure the plate voltage? And how do I keep it safe?
 
Re: The right way to bias with bias current checkers?

Nightburst said:
Thanks for helping! I don't have the bias rite, I got these made by a tech so I can use them with a multimeter. Where do I measure the plate voltage? And how do I keep it safe?
Click to expand...

Having a multimeter is a great place to start. Check this link out:

http://www.laneyforum.com/phpBB2/viewtopic.php?t=56

If you have any questions I won't be to far away today, working on a very large report. I am refining this instruction process as more people do it.

The basic premise here is measuring the voltage of pin 3 to ground on a EL34 or 6L6 socket or pin 7 to ground on a EL84 socket from inside the chassis. Any time you go inside an amp chassis, you have exposure to high voltages. Be careful.
 
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Re: The right way to bias with bias current checkers?

wixedmords - thanks so much!

Haven't fully digested all of your work plus the Aiken & Duncan pieces, but the basic concepts are certainly there.

Chip

P.S. On a 2-tube, push pull amp with fixed bias, would it be beneficial to have one pot to set overall bias and a second pot to balance between the two tubes by ear (to reduce hum)?

The alternative would be a bias pot for each tube.
 
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Re: The right way to bias with bias current checkers?

Fresh_Start said:
P.S. On a 2-tube, push pull amp with fixed bias, would it be beneficial to have one pot to set overall bias and a second pot to balance between the two tubes by ear (to reduce hum)?

The alternative would be a bias pot for each tube.
Click to expand...

There is an added level of control with an amp that has a bias pot for each pair or even each tube. This level of control would allow you to compensate for severely unmatched tubes, for without the separate bias pot you would need to bias using the hotter tube as the upper-most reference. Multiple bias pots would be needed when using integrated quads, so you can tailor the bias of each pair.

Some like the sound quality of mismatched tubes. As long as the tubes are matched fairly close, you should be fine. Bias using the hottest.
 
Re: The right way to bias with bias current checkers?

wixedmords said:
Some like the sound quality of mismatched tubes. As long as the tubes are matched fairly close, you should be fine. Bias using the hottest.
Click to expand...

I'm running GT6L6GE/GT6L6R in my 6505+. Both sets are power rated at 6 though.

Sounds great to me, more lively than the stock ruby tube 6L6s.
 
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Re: The right way to bias with bias current checkers?

Bogner told me that 35mA is what they recommend, but I set mine at 36mA.
I'm also using JJ EL-34's, and you're using E-34L's, so a little hotter is fine with those tubes.

I'd be concerned about a tube reading 16mA though. You should trouble shoot that by putting one of your old tubes in that slot, and measuring it again.

If you haven't seen it, check out my 'Biasing a Jubilee' thread in the Vault. Lots of good pictures.
 
Re: The right way to bias with bias current checkers?

Anything less than starting with plate voltage is just incorrect and lazy. ;)
 
Re: The right way to bias with bias current checkers?

wixedmords thanks man, that was an interesting article and I am starting to get it. Too bad I got a bad tube in my batch :(.
I am being really carefull so I ain't touching anything inside!

Thanks for your input on this Gearjoneser! I was already wondering how you did it since you got the exact same amp. I am definately checking out your tutorial on the Jubilee!

I don't think it will be a good idea to mix different type of tubes in the power section? I want all new tubes anyway so I will have to get another tube I'm afraid. Also the bias pot bugs me, it won't go further back so the coldest I can bias these tubes is around 39ma. Anyone got tricks to bring it down some? There should be some kind of reset procedure?
 
Re: The right way to bias with bias current checkers?

bump for my last question.
I'm too scared to measure inside the amp!

Now I got a set of Electro-Harmonix EL34's. They read around 46mA with the bias pot all the way down! Now Bogner recomends 36mA and my last tubes were done by a tech at 34mA so this can't be good?!
 
Re: The right way to bias with bias current checkers?

I've always used JJ EL-34's because they fall into the range better. One time I tried Svetlanas, and the lowest they'd go was 42mA, so I went back to the JJ's.

I called Bogner about this, and they said the bias range is set for the original tubes the amp came with, and that some other brands are hotter or colder.
He said the solution was to change a bias resistor near the pot, but I didn't want to start dabbling with that.

If I were you, I'd send an Email to Bogner's Customer Service. Those guys are really helpful. They may tell you to change that resistor, take it to a tech they know of in your area, or use a specific brand of tubes. I know this is a hassle, and I've gone through it with my Bogner and a few other amps.
 
Re: The right way to bias with bias current checkers?

Gearjoneser said:
I've always used JJ EL-34's because they fall into the range better. One time I tried Svetlanas, and the lowest they'd go was 42mA, so I went back to the JJ's.

I called Bogner about this, and they said the bias range is set for the original tubes the amp came with, and that some other brands are hotter or colder.
He said the solution was to change a bias resistor near the pot, but I didn't want to start dabbling with that.

If I were you, I'd send an Email to Bogner's Customer Service. Those guys are really helpful. They may tell you to change that resistor, take it to a tech they know of in your area, or use a specific brand of tubes. I know this is a hassle, and I've gone through it with my Bogner and a few other amps.
Click to expand...

Thanks gearjoneser! That clears it up for me.
I didn't realise tubes have different ranges as well, I thought that within the same category (EL34, E34L,etc.) the same range would apply.
Too bad about the tubes but I ain't messing with my amp just to make it easier. Another well paid lesson about tube amps for me.
Call it character of the amp, which is a very picky one but boy does it deliver when you treat it right! :firedevil So i'll accept it for what it is.
Mine came standard with svetlana's I think? They always sounded good in this amp.
I've had 2 quartets of JJ's that were malfunctioning so far...
 
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