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Post subject: New tubes in a '91 Bassman
Posted: Sun May 10, 2015 9:13 pm
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Location: Seattle, WA
I just picked up a 1991 '59 Bassman Reissue. It is all stock, and a little beaten up, and sounds great. It has what appear to be some newer JJ tubes.
I'm going to put some NOS tubes in it, and read that it is a fixed bias amp. I'm not sure what this means in terms of installing new tubes. Can I just put them in? Do I need to take the amp to a tech first?
Thanks, Stu.
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Post subject: Re: New tubes in a '91 Bassman
Posted: Mon May 11, 2015 1:40 am
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Joined: Fri Feb 05, 2010 4:31 am
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If you put new output tubes you ( a qualified tech ) must check bias and adjust if needed .

Bias adjust is for output tubes only ,not preamp tubes ( 12XX7)

Never put output tubes without checking bias .


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Post subject: Re: New tubes in a '91 Bassman
Posted: Mon May 11, 2015 2:10 am
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stratele52 wrote:
If you put new output tubes you ( a qualified tech ) must check bias and adjust if needed .

Bias adjust is for output tubes only ,not preamp tubes ( 12XX7)

Never put output tubes without checking bias .


Only the "LTD" version of the 5F6-A re-issue Bassman has an adjustable bias pot.

The bias level is fixed on the standard tweed Bassman.

Arjay

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"Here's why reliability is job one: A great sounding amp that breaks down goes from being a favorite piece of gear to a useless piece of crap in less time than it takes to read this sentence." -- BRUCE ZINKY


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Post subject: Re: New tubes in a '91 Bassman
Posted: Mon May 11, 2015 2:16 am
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I'm sure you know what is call " a fixed bias " do not mean the amp have no pot .
Some amp have adjustable fixed bias , some have non adjustable fixed bias

http://www.thetubestore.com/Resources/M ... Bias-Types

You know that


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