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Fender Harvard 5F10

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  • #16
    Wow, that's darn near Mexico brother....what shock from VT!!
    I flew down to Carlsbad, NM two summers ago, a couple hundred miles east of you.... hot as all heck.
    That is about the furthest I've gone in 4-5 years.
    Bruce

    Mission Amps
    Denver, CO. 80022
    www.missionamps.com
    303-955-2412

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    • #17
      Bruce, how would you go about removing the negative feedback from the 5F10 circuit?

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      • #18
        There is a 56K resistor that takes the output transformer signal & injects it into the cathode of 1/2 of the 12AX7.
        http://music-electronics-forum.com/a...5f10_schem.pdf
        That is the NFB resistor.
        If you do not want NFB, remove the connection.

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        • #19
          Originally posted by Jazz P Bass View Post
          There is a 56K resistor that takes the output transformer signal & injects it into the cathode of 1/2 of the 12AX7.
          http://music-electronics-forum.com/a...5f10_schem.pdf
          That is the NFB resistor.
          If you do not want NFB, remove the connection.
          Or get a 50K to 100K pot to put in series with the 56K resistor, wire it as a variable resistor and mount it somewhere so you can increase or decrease the amount of NFB.
          I don't think those amps had two speaker jacks so.... you have to be selective on where to and how to mount the pot so as not to wreck the vintage value.
          Bruce

          Mission Amps
          Denver, CO. 80022
          www.missionamps.com
          303-955-2412

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          • #20
            My Harvard copy is my favorite guitar amp.
            http://i422.photobucket.com/albums/p...s/Harvard1.jpg

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            • #21
              Originally posted by Bruce / Mission Amps View Post
              I frequently find that these old Harvard amps exhibit an ultrasonic oscillation right at about 75% to 90% full output power.... must be the wiring layout... if you remove the negative feedback, it goes away.
              I have a Harvard circuit that I built up a while back that does exactly this but I haven't worried too much about it because it's just a little shop amp that I don't need to crank. I know this is an old thread but can anyone comment on how to avoid this problem without cutting the nfb? I wouldn't mind cutting it but would also like to know if there is a real fix. Thanks
              ~Semi-No0b Hobbyist~

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