Weird sound on Proluxe build

Discussion in 'Shock Brother's DIY Amps' started by Cfidave, Sep 8, 2019.

  1. Cfidave

    Cfidave TDPRI Member

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    Built my second 5E3P and have a faint motor boarding sound, nothing plugged in. Reminds me of vibrato ticking from a vibrato optocoupler. Any ideas what that might be? Voltages are all in order.
     
  2. sds1

    sds1 Tele-Afflicted

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    Does it start and stop intermittently? Could be interference from nearby electronics -- routers, modems, cell phones, etc.
     
  3. stantheman

    stantheman Doctor of Teleocity

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    Cracked socket?
     
  4. wabashslim

    wabashslim Tele-Holic

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    Leaky/bad/cold soldered filter cap?Are your voltages around the tubes good & solid or do they drift some?
     
  5. FenderLover

    FenderLover Friend of Leo's

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    What size cap did you use for the preamp filter? Motorboating is often traced back to power supply filtering, namely lack of it, (or bad cap) and interaction between the four triode sections the preamp cap supplies. To test the idea, just parallel another cap with the preamp filter and see if there is a change.
     
    Last edited: Sep 8, 2019
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  6. Cfidave

    Cfidave TDPRI Member

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    Not intermittent, continuous. Voltages are solid in spec for all dc voltages. Power supply caps are 40,40, and 22 for the preamp filter. I will try paralleling another cap across the 22. I am also going to replace the V1 socket as it is very noisy if probed. Tried cleaning and re-tensioning but still has way to much static and pop. Thanks for the input.
     
  7. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    So if it's continuous, is it affected by any controls? If not, can you make it better or worse by moving some wires around? Lead dress can often cause motorboating or oscillation issues.
     
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  8. cousinpaul

    cousinpaul Friend of Leo's

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    My Proluxe started out with fixed bias as per Weber's layout and noise was a problem. I eventually converted it to cathode bias which quieted it down. I've read some posts on the old Music Electronics Forum that document the same problem with the fixed bias circuitry. If you have the parts, switching to cathode bias might be worth a try. If it helps, you'd at least have a direction to pursue.

    I also occasionally get noise from the un-used input jacks but plugging a cable into them a couple of times will generally straighten it out.
     
  9. RottenTheCat

    RottenTheCat Tele-Meister

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    Check for leaky coupling capacitor. Should be darn near zero volts DC on the grids.

    Check the lead dress for possible issues.

    Just how fast is the motorboat?
     
  10. RottenTheCat

    RottenTheCat Tele-Meister

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    Also limit the size of the coupling caps into the phase inverter
     
  11. dunehunter

    dunehunter Tele-Holic Double Platinum Supporter

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    Just recently experienced that motor-boating too. It was on my 5E3 build (I've got a thread going here somewhere that lays this all out). The motor-boating for me appears to have been solved by a swap of the 12Ax7 which apparently had a faulty section. However, my build had a number of other issues when I first started it up so your mileage may vary on this, considerably. But, worth a shot if you haven't swapped out a tube or two in the preamp section.

    Just a thought from someone just learning the complexities of tube guitar amp electronics.
     
  12. Cfidave

    Cfidave TDPRI Member

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    Thanks for all the input. I believe my problem was one of the power tubes. I was running 5881's at 65% max dissipation, decided to swap in 6L6GC's and the problem went away. I should have swapped tubes sooner.







    Proluxe2c.jpg
     
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  13. Cfidave

    Cfidave TDPRI Member

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    Have another problem that has me baffled. I have a very low volume 60 cycle hum. This is with No tubes at all in the amp. It has to be AC getting into the output some how. I have tracked down all sources of AC that I can think of:
    Transformer mains are putting out 320vac each, bias is 50vac, heaters are 5.4 volts & 6.5 volts. I have done the following:

    Rechecked grounds, HV center tap, Heater center tap, Bias ground. HV center tap is grounded at first filter cap.
    Tried different house circuits, no change. ( other amps don't hum at any house location)
    My PT & OT are rather close so I shielded with copper foil & metal plate both transformers, no change.
    Paralleled another 50/100 cap with the current two caps, no change.
    Power supply caps all read good, and grounds seem good.
    Ran heaters off of a 6 volt battery, no change at all.
    Re-soldered the entire rectifier leads.


    I can probably live with this hum as you need to be within 2 or 3 feet of the amp to hear it and it does not change with volume, when tubes and guitar are connected.. I would love to know how this is occuring, very strange.
     
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