# Wild Bill or the other pros



## Rugburn (Jan 14, 2009)

There have been a few posts lately regarding "fixed bias" amps. My old Princeton Reverb is fixed bias, but I'm quite sure the tech who last worked on it rebiased the amp when I had it retubed. A new resistor was soldered in place of the old one. Is there a way I can have it modified to be like these newer amps, so I can just go out and buy power tubes when needed. I'd love to avoid paying the hefty bench charge every time I need new tubes.
Any advice would be greatly appreciated.

Shawn.


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## greco (Jul 15, 2007)

I'm interested in this also as I have a Princeton Reverb that need's a checkup.

What year is yours?

Cheers

Dave


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## bagpipe (Sep 19, 2006)

Probably best to wait for "The Master" to chime in, but I found this site. I'm guessing you'd also need some way of measuring the bias voltage and I'm not sure you'd get it with this mod?

http://www.fenderholic.com/Prince bias mod.htm


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## Rugburn (Jan 14, 2009)

Hi Dave, it's a '66 with a Weber 10a100 speaker. I posted a couple of pics in the "What Amp Do You Have" thread in this forum. I guess ultimately I should go for an adjustable bias pot mod. Though, after reading about these new school amps I'm feeling laaazzy. :smile:


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## Ripper (Jul 1, 2006)

bagpipe said:


> Probably best to wait for "The Master" to chime in, but I found this site. I'm guessing you'd also need some way of measuring the bias voltage and I'm not sure you'd get it with this mod?
> 
> http://www.fenderholic.com/Prince bias mod.htm


Bagpipe that mod would still require you to take your bias voltage reading from the power tube.

Making a fender amp adjustable bias is very simple and there is tones of info on the web about it . That doesn't however make it "auto" biasing (cathode) or plug and play if you will. It makes it so instead of changing a resistor to get your proper bias voltage you can adjust the pot, so it makes it much quicker and easier. 

Biasing is about many things, some bias for tube longevity, some bias for tone. By having an adjustable bias you can tweak the bias to get the tone/respsone that suits YOUR tastes and needs. Cathode biasing doesn't allow for you to tweak your tone, it sets it to what "the tube" feels is best.


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## Wild Bill (May 3, 2006)

Ripper said:


> Bagpipe that mod would still require you to take your bias voltage reading from the power tube.
> 
> Making a fender amp adjustable bias is very simple and there is tones of info on the web about it . That doesn't however make it "auto" biasing (cathode) or plug and play if you will. It makes it so instead of changing a resistor to get your proper bias voltage you can adjust the pot, so it makes it much quicker and easier.
> 
> Biasing is about many things, some bias for tube longevity, some bias for tone. By having an adjustable bias you can tweak the bias to get the tone/respsone that suits YOUR tastes and needs. Cathode biasing doesn't allow for you to tweak your tone, it sets it to what "the tube" feels is best.


See? You didn't need me! Ripper is 100% right!

What's happening with the type of amps you originally mentioned is that they have the bias set cold enough so that no matter what tubes you plug in they won't burn themselves out.

They will also likely sound "lame-ass". That's the problem with many amps that do this. 

Do what the good Ripper says! Let your amp be easily adjusted to put the bias on the "sweet spot" whenever you change the output tubes.

If you are really "thrifty" (didn't want to say 'cheap'!) you could get some tubes from the tubestore.com and have them biased. Then always order tubes of the same "match' number. They shouldn't need re-biasing.

Of course, "should" depends on how lucky you feel!:smile: The nice thing about rebiasing new tubes is it gives a tech a chance to look around inside your amp and see if anything is looking "ugly"! It's like how a good mechanic when he does an oil change will look around to make sure the engine isn't falling out.

:food-smiley-004:


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## Rugburn (Jan 14, 2009)

Thanks Ripper & WB. For the record, I did say "and other pros". :smile:


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## GTmaker (Apr 24, 2006)

Wild Bill said:


> Of course, "should" depends on how lucky you feel!:smile: The nice thing about rebiasing new tubes is it gives a tech a chance to look around inside your amp and see if anything is looking "ugly"! It's like how a good mechanic when he does an oil change will look around to make sure the engine isn't falling out.
> 
> :food-smiley-004:


HEy Wild Bill....My Fender Bassman LTD could use an "oil change".
Whats your base price for kicking the tires and checking the oil stick?


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