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5F1 Troubleshooting

Discussion in 'Shock Brother's DIY Amps' started by woodbutcher, Sep 15, 2018.

  1. woodbutcher

    woodbutcher Tele-Meister

    178
    Jun 9, 2012
    Lake Stevens, WA
    I built a Boothill 5F1 several years ago. Since I'm not a player, I never did much with it.

    Recently I had a harmonica player try it out to see what kind of tone it would produce. At a mid level volume with full gain on the It has a bit of hum at higher volume but the biggest problem was the crackling it would occasionally put out. This seemed to occur after a loud signal was played.

    Today I turned it on and did some probing with a bamboo skewer. The number one pin on the 12AX7 tube (I'm actually using a JJECC83s) was creating a microphonic effect, when tapped. Could this be my problem? I don't have a spare tube on hand to swap out.

    Thanks,
    Mark
     

  2. sds1

    sds1 Tele-Holic

    Age:
    42
    658
    May 4, 2017
    Orlando, FL, USA
    Not hearing the exact thing you are, but it's pretty normal for tapping around V1 to be noisy in the form of a ringing microphonic sound.
     
    JD0x0 likes this.

  3. corliss1

    corliss1 Friend of Leo's Gold Supporter

    Sep 13, 2008
    Lansing, MI
    Well, there isn't a whole lot you can do without spare tubes. You only need one 12ax7 and one 6v6, as the rectifier tube will either work or not.

    Does any other area of the circuit make noises? You could try just taking the tubes out and putting them back in to see if "re-seating" them cures the issue. Static is often a cold solder joint or a sketchy tube connection, and something just re-seating the tubes cleans the pins off enough to fix it.
     
    dan40 likes this.

  4. dan40

    dan40 Tele-Holic

    933
    Aug 19, 2015
    Richmond Va
    Noises heard through the speaker when probing the preamp tubes are fairly normal. Probing v1 will produce the most noise because the sound is sent through more gain stages as it travels to the speaker. The crackling noises you heard at high volume may indicate a bad solder joint or dirty tube socket. How long did the amp sit unused? The electrolytic capacitors in the amp need occasional voltage through them to keep them healthy and "formed". If the amp has sat unused for a number of years there is always the chance that a cap has gone bad. I would try pulling the tubes and reinserting them just to clear away any oxidation that may have formed on the pins first. That may be all it needs.
     

  5. corliss1

    corliss1 Friend of Leo's Gold Supporter

    Sep 13, 2008
    Lansing, MI
    Looks like @dan40 and I are on the same page :D
     
    dan40 likes this.

  6. woodbutcher

    woodbutcher Tele-Meister

    178
    Jun 9, 2012
    Lake Stevens, WA
    Thanks for all the feedback. All the ideas are greatly appreciated. I had not found any other joints that created any noise when tapped. The amp sat in my living room for about six years.Will try the tube pin 'cleaning' next. Maybe pick up some spare tubes, just because. Am hoping to get rid of the hum at high volume as well as the static so that the amp can be mic'ed for recording use. The amp was producing the best harmonica tones when cranked about 3/4 volume but the noise level was getting too noticeable.
     

  7. Silverface

    Silverface Poster Extraordinaire Platinum Supporter

    Age:
    66
    Mar 2, 2003
    Lawndale CA
    If you clean the tube sockets be sure to use something that is a "cleaner/lubricant". Electronics oils contained in those products prevent corrosion, which can occur rapidly is plain "contact cleaner" is used. Let the cleaner/lube dry before powering up.

    6 years is not necessarily an overly-long storage time, but filter caps can still crystallize within that time, depending on the quality and how old the caps were when installed. If they sat on a shelf for years they may be shot. Many have date codes on them, and filter caps over 15 years old - especially ones that have also gone through extended storage - I replace.

    It would also be helpful if you posted pictures of the chassis - some issues are relatively obvious.
     
    dan40 likes this.

  8. woodbutcher

    woodbutcher Tele-Meister

    178
    Jun 9, 2012
    Lake Stevens, WA
    Getting back to this diagnosis. Have cleaned the tube pins/sockets, without any improvement.

    Am wondering if the hum at higher volumes may be due to the transformers. I used the classic tone 40-18019 PT and the 40-18031 OT to get more wattage out of the amp.

    View attachment 550238 View attachment 550239
     

  9. woodbutcher

    woodbutcher Tele-Meister

    178
    Jun 9, 2012
    Lake Stevens, WA
    Sorry not good at adding photos.

    40-18019 Power Transformer.JPG

    40-18031 Output Transformer.JPG
     

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