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Post new topic Can the blues Jr. be Biased
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Author Topic:  Can the blues Jr. be Biased
Greg Lambert


From:
Illinois, USA
Post Posted 25 Dec 2017 7:58 pm     Reply with quote

OR is it fixed?
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Dave Meis


From:
Olympic Peninsula, Washington, USA
Post Posted 25 Dec 2017 10:46 pm     Reply with quote

I have an early one, and it was fixed. I sent it to Billm, and he put a bias pot in it. I don't know if the new ones have them, but the old version didn't.
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Bill A. Moore


From:
Silver City, New Mexico, USA
Post Posted 26 Dec 2017 8:04 am     Reply with quote

I believe it's cathode biased. Just a matter of changing a resistor, if necessary to bias it.
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ajm


From:
Los Angeles
Post Posted 26 Dec 2017 9:02 am     Reply with quote

In the schematic that I saw on the internet.....

The Blues Jr is not cathode biased.

It is fixed bias and not adjustable........stock.
A bias pot could easily be added.
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John Dahms


From:
Perkasie, Pennsylvania, USA
Post Posted 28 Dec 2017 5:35 pm     Reply with quote

Blues Jr. amps usually come biased running way too hot from new (about the only tube amp I can think of that comes this way- many are too cold). This sometimes causes the power tube sockets to distort from heat and fail.
Running more negative bias cools them down and opens up the tone for more headroom and I think more useful range. There are articles on how to do this several places on the web.


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Terry Lovett


From:
Texas, USA
Post Posted 5 Jan 2018 12:25 pm     Reply with quote

Yes, the Fender Blues Jr has a fixed bias circuit and can be adjusted. If you have a tech you use, make sure he knows what instrument you use and how you like it set up. If you have a current tech that knows how to set it up, you are better off employing their skill (a Fender certified tech will know); if you know how to do this safely, then you'll know where and how to set it. I don't suggest anyone doing this that's not highly qualified.....you'll have to be working in a live chassis with dangerous voltages. Be safe..

PS - if you haven't already, I would replace those IC filter caps with known good capacitors....not a fan of the IC's....well worth the expense
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Carl Mesrobian


From:
Salem, Massachusetts, USA
Post Posted 5 Jan 2018 4:46 pm     Reply with quote

Terry I love your signature line from Jim Williams Smile

Speaking of caps, other than Sprague Atoms, have you used the TAD or F&T brands ? Thoughts?
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"The better it gets, the fewer of us know it." Ray Brown
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Terry Lovett


From:
Texas, USA
Post Posted 5 Jan 2018 9:31 pm     Reply with quote

Carl Mesrobian wrote:
Terry I love your signature line from Jim Williams Smile

Speaking of caps, other than Sprague Atoms, have you used the TAD or F&T brands ? Thoughts?


Yes Carl, I have used the Atoms for many years without issues but, their extraordinary price increases have forced me to look harder at alternatives. I have been using the F&T's for while also....I actually like their published specs which can be better than the Atoms. Time will pan out these competitive caps but, supply and demand will always steer the economics. Even better specs can be had with radial configured Panasonics.....perhaps anything can be a better alternative to the IC's. I've seen the IC's fail too early and performance can be hit-n-miss

http://uk.farnell.com/panasonic/eeuee2w470/capacitor-47uf-450v-16x31-5mm/dp/1673505
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Steven Paris


From:
Los Angeles
Post Posted 10 Jan 2018 10:45 am     Reply with quote

Terry Lovett wrote:
http://uk.farnell.com/panasonic/eeuee2w470/capacitor-47uf-450v-16x31-5mm/dp/1673505

Ah, but that's a RADIAL lead cap---tougher to fit. Have you a suggestion for an AXIAL lead capacitor?
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Carl Mesrobian


From:
Salem, Massachusetts, USA
Post Posted 10 Jan 2018 12:08 pm     Reply with quote

Here's a bunch - (edited)

https://www.mouser.com/Passive-Components/Capacitors/Aluminum-Electrolytic-Capacitors/_/N-75hqt?P=1z0z819Z1z0wrk9Z1yx4ard&Ns=Pricing|0
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"The better it gets, the fewer of us know it." Ray Brown
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