Blues Junior fixed bias mod, anyone know what resistor type?

Discussion in 'Amp Tech Center' started by Chunkocaster, Oct 16, 2018.

  1. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    Must be a ***** to get your keys out of your pocket!

    :lol:
     
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  2. Chunkocaster

    Chunkocaster Poster Extraordinaire

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    It's not bad work is it, keeps you fit and the hours can be good and flexible. You can get a sense of satisfaction upon finishing every job and once you get a rhythm going life feels good most of the time. It's similar to learning a new song or going a step forward with your playing.
    It's also nice working outdoors and you get to meet a lot of people in different locations every week or two. I learnt from a old Italian concreter I worked with for the first couple of years doing footpath and road construction contracts mixed with private jobs.
     
    Last edited: Oct 20, 2018
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  3. Chunkocaster

    Chunkocaster Poster Extraordinaire

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    It must chafe badly on a hot summers day.:D
     
    Last edited: Oct 20, 2018
  4. SSL9000J

    SSL9000J Tele-Meister

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    I actually like to use adjustable vitreous enamel resistors, like this:
    [​IMG]
    The 400 - 1000 ohm, 10 - 12 watt variety works well. "Set and forget," as the saying goes.
     
  5. SSL9000J

    SSL9000J Tele-Meister

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    [​IMG]
     
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  6. peteb

    peteb Friend of Leo's

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    after a driveway was poured close by this weekend I became interested in the question, should a driveway have expansion joints? I assumed they would.


    It turns out that (crack) control joints are preferred. the inevitable cracks follow the control joints and the control joints (at least partially) carry the load across the joint where the load is not carried across expansion joints.




    the fact that cracks occur in all concrete structures blows my mind.


    I have been watching the construction of an elevated light rail line. Each support looks like a T and each side of the T will carry a train. Cracks in this situation would seem intolerable, but I guess they are going to happen.
     
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  7. peteb

    peteb Friend of Leo's

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    word is

    if the cracks are really small its OK. like too small to see.


    if the crack is visible, its a problem.
     
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  8. mturk

    mturk TDPRI Member

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    Change the 22K or 33K resistor to 27K. Forgot which one.
     
    Last edited: Mar 4, 2019
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  9. tubeswell

    tubeswell Friend of Leo's

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    I know this will probably be frowned upon, but if you want a simple 1-resistor mod, then solder tack 150k in parallel with R51 - see attached schematic (changes the upper leg resistance to 27k. 22k/(22k+27k)=45% of Vin (Vin is about -26V).

    Shifts the bias voltage to about -11.5V (which is better than the stock -8.0V it comes with from the factory)

    Although, strictly speaking, you should measure plate current and plate voltage etc, and install an adjustable bias voltage mechanism... but Fender obviously didn't care about any of that when they designed the BJ, so...

    (This has been field tested and approved, by me)
     

    Attached Files:

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