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Thread: Fender Deluxe Hot Rod amp

  1. #1
    Forum Member
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    Jan 2016
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    Fender Deluxe Hot Rod amp

    Hi

    I am new to this forum and I badly need some help. I recently bought a used Fender Deluxe Hot Rod amplifier from a secondhand store. The amp is working but I decided to check and set the bias correctly for this amp. Downloaded the service manual from the net. According to the manual, the bias setting at TP30 should be +60mv. As instructed, without any signal applied, I measured the voltage at this point. My DC multimeter shows a reading of approx 30.5mv. I tuned the variable pot R82 to get a reading of +60mv, but the highest reading I can get is approx 46mv at the pot fully clockwise. I do not understand why I am unable to tuned to 60mv. Is it because the mains voltage shown on the manual is for 120V AC, but locally we use 240V AC or is it due to some component failure or problem with the tubes. Please advice.

    Thanks

    Carlos

  2. #2
    Forum Member mickeydg5's Avatar
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    May 2016
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    Re: Fender Deluxe Hot Rod amp

    Hello Carlosraj7
    I suppose you checked to make sure you have two good power tubes. Make sure both are seated properly and operating as well. With one tube not operating you will only read one tube at TP30.

    There could be an issue with the cathode circuit. If R66 1 ohm is partially shorted the bias will measure low.

    Also make sure the voltage coming off the bias trimmer R82 wiper tab is in about the -50VDC range. That connects between R59 and R60. Follow each route from there to pin #5 of each power tube control grid to make sure proper negative voltage show up at the socket lugs.
    Last edited by mickeydg5; 05-10-2016 at 02:42 PM.

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