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Post subject: Re: 100W Bias control
Posted: Thu Feb 13, 2014 5:27 pm
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You can always try different tubes in the PI position. 12AU7 or 12AY7 and see what happens. Even a 12AX7 maybe worth a try, though the potential extra current demand may shorten a 12AX7 life.

A pot on the feedback will also give you some control over OD.


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Post subject: Re: 100W Bias control
Posted: Thu Feb 13, 2014 7:38 pm
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That's just it, a master volume limits what goes to the output tubes. I want to be able to drive them instead of driving the pre-amp tubes.

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Post subject: Re: 100W Bias control
Posted: Thu Feb 13, 2014 8:12 pm
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I think that the variable feedback to ground (ala: Presence control) like the type used in the Brownface era amps, maybe worth a look at.

http://www.webphix.com/schematic%20heav ... _schem.pdf


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Post subject: Re: 100W Bias control
Posted: Fri Feb 14, 2014 3:55 am
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jimolson1963 wrote:
That's just it, a master volume limits what goes to the output tubes. I want to be able to drive them instead of driving the pre-amp tubes.


Attenuator , the only way :D


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Post subject: Re: 100W Bias control
Posted: Fri Feb 14, 2014 7:32 am
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Bah... attenuator... lol! I was hoping there would be a better way.

That 6G6-B schematic is missing the bias adjuster. I'm guessing that is a fixed bias setup?

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Post subject: Re: 100W Bias control
Posted: Fri Feb 14, 2014 8:27 am
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jimolson1963 wrote:
Bah... attenuator... lol! I was hoping there would be a better way.




Sure there is a better way , buy a low power amp :lol:


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Post subject: Re: 100W Bias control
Posted: Fri Feb 14, 2014 9:28 am
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Hahaha. :lol:

If this had a pristine case I'd just put it back to stock and sell it but the faceplate is bent and scratched up and it needs new tolex and a grille cloth to look good. So it'll be my experimental amp I guess.

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