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Post subject: Bassman tube substitution
Posted: Fri Feb 04, 2011 12:07 pm
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I have a 1965 Bassman, (converted into a 1x12 combo. I would like to change the preamp tube in the normal channel to something with a little less gain. Does anyone know which tube that would be?

Thanks!


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Post subject: Re: Bassman tube substitution
Posted: Fri Feb 04, 2011 12:26 pm
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Start with a 12AT7 and see how that sounds. The next step down, gain-wise, would be the 12AY7. Below that is the 12AU7, which I doubt will serve your purpose(s).

Best of luck, HTH

Arjay

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Post subject: Re: Bassman tube substitution
Posted: Fri Feb 04, 2011 5:09 pm
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[quote="lightspeedfran"]I have a 1965 Bassman, (converted into a 1x12 combo). I think I'm gonna cry......... :x Mike

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Post subject: Re: Bassman tube substitution
Posted: Fri Feb 04, 2011 9:25 pm
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If you are used to the tweed Bassman tone, you'll prolly like the 12AY7 (6072). It's what Leo put into several of his tweed units. Including some Bassmans. If you find that the 12AY7 doesn't have the headroom or clean top end at volume, it's prolly because the "ideal" idle setting of a 12AY7 is a little different than a 12AX7.

12AY7 likes a little less plate voltage than a 12AX7. Kinda illustrated in the Bassman (5E6A) circuit. Check out the second stage 12AY7 setup versus the PI (12AX7) next to it. If the tone is fine... don't worry about the various tube switches. As they are cathode biased, Class "A" settings--which are somewhat self-leveling to a large degree. Fine tuning plate voltages just insures the greatest/cleanest "swing" in signal current.

http://www.ampwares.com/schematics/bassman_5e6a.pdf


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Post subject: Re: Bassman tube substitution
Posted: Sat Feb 05, 2011 12:19 am
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BMW2002Ti wrote:
If the tone is fine... don't worry about the various tube switches. As they are cathode biased, Class "A" settings--which are somewhat self-leveling to a large degree. Fine tuning plate voltages just insures the greatest/cleanest "swing" in signal current.


+1

Unless the tube red-plates it'll prolly be fine.

Arjay

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