mojohand
1 post
Dec 24, 2016
8:00 AM
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I would like to know how cold i should biais a tweed 5e7 to have a fatter tone , right now mine is 34 ma at 342 v i have put a 12dw7 as phase inverter and it has fatten the tone, but is it worth to biais colder than 34 ma ?
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1847
3916 posts
Dec 24, 2016
12:06 PM
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a vintage bandmaster is a wonderful amp. here is an interesting article on amp bias.
http://tone-lizard.com/biasing/
myth #1: ALL 6L6’s SHOULD BE BIASED AT 40mA.
Or 35 mA, or biasing strictly to any specific ‘magic’ number. It’s all wrong. You are not taking into account the vast differences in output transformers and tubes.
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Last Edited by 1847 on Dec 24, 2016 12:28 PM
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mojohand
2 posts
Dec 24, 2016
12:18 PM
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Maybe i should have mentionned my amp is a victoria bandmaster and it has 5881 power tubes , it is a wordefull amp stock for guitar , since i run it with two 8 inches ( 4 ohms) and one ten ( 8 ohms) ( all webers) in seri- parall, for a total 4 ohms load instead of the 2,6 ohms when stock it sound way much better for harp, i would like to know if 34 ma is normal biais or cold biais for that amp
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mojohand
3 posts
Dec 24, 2016
12:24 PM
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Thanks for the info
Last Edited by mojohand on Dec 24, 2016 12:36 PM
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Bugfan
55 posts
Dec 26, 2016
4:50 AM
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I have a much modified pa100 with 6l6 and i think they sound god at 17mA. I've got 5881 tubes in a modified special 44 and the lower the bias the better they sound i reckon.
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Harpaholic
901 posts
Dec 26, 2016
2:43 PM
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Best way is to use your ear, It will tell you when it's too cold.
It may sound best in the low to mid 20's??
Don't bias it like a guitar amp if your using it for harp!
Let us know what works for you.
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LSB
240 posts
Dec 26, 2016
5:40 PM
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"Don't bias it like a guitar amp if you're using it for harp!"
Why is that?
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Harpaholic
902 posts
Dec 27, 2016
5:30 PM
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Because they can sound better with a colder bias for harp, they don't distort as quick, and extend tube life.
There is a lot of factors in play, tubes, amp mods, B+, amp type, etc; a colder bias can reduce gain, feedback, and harshness.
Too cold and it will sound lifeless.
That's why I recommend using your ear.
A lot of people run 50-60% dissipation n guitar amps as opposed to 70% because they sound better to their ears.
Try a NOS JAN 12AT7 in the PI, there still cheap.
Let us know what works for you.
Last Edited by Harpaholic on Dec 27, 2016 5:33 PM
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tmf714
2961 posts
Dec 27, 2016
5:42 PM
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Try 2 5881's and a GZ 34 rectifier at 36 MA-get back to me here. I am sure the results will be positive.
More headroom-but your plate voltage will be higher.
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