5F6-A virtually no sound

Discussion in 'Shock Brother's DIY Amps' started by Clintstone, Aug 4, 2019.

  1. Clintstone

    Clintstone Tele-Meister

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    So I just got my bassman head project wired up and it has issues. I followed Rob Robs start up procedure using a light bulb limiter and things went well, until I plugged in a speaker and a guitar. With the channel one volume and the master volume (Frondelli) all the way up there is almost no speaker output. I swapped around tubes in the first 3 spots (all 12ax7) and still no volume. So I pulled out my trusty DVOM and I have some strange voltages. I wrote out a chart like Robs and compared voltages and here is what I found. 20190804_161740.jpg
     
  2. Snfoilhat

    Snfoilhat Tele-Afflicted

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    Phase inverter, V3, should have much lower voltages on the cathodes (pin 3 and pin 8). Such high voltages imply that too little current is flowing through the triodes. Check the tail resistor's value and its ground connection -- that's the 10k. Check the cathode bias resistor's value and its connections to the cathodes (pins 3 and 8) and the tail resistor. That's the 470R. Ensure that you haven't inadvertently swapped 47k or 470k for the required 470.

    Once more current flows through the triodes of V3, you will see the plate voltages (pins 1 and 6) drop too.

    Good luck!
     
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  3. tubedood

    tubedood Tele-Meister

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    I am learning every day (as are most of us on this fine site) and I just finished a lil 5F2-A.

    My voltages are much lower than yours... all the old fenders used similar voltages I believe. My 6V6 plate sees about 335 volts. The 12ax7 sees on the plate about 175. I haven't given this amplifier much higher voltages so I don't know if that has anything to contribute.
    To me the voltages seem very high?
     
  4. D'tar

    D'tar Friend of Leo's

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  5. jsnwhite619

    jsnwhite619 Friend of Leo's

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    My first bigger amp build was a Tweed Super. Spent two weeks troubleshooting low output. Turns out I had two wires mixed up on V2 or V3. Simple fix but was a bear to find.



    Sent from my XT1585 using Tapatalk
     
  6. tubeswell

    tubeswell Friend of Leo's

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    What the others said. The LTP inverter is wired incorrectly. The high voltage on the plate pins (1 and 6) is a clue that no tube current is flowing. Also you have high voltage on the cathode pins (3 and 8) indicating miswiring.
     
  7. Clintstone

    Clintstone Tele-Meister

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    Well I feel mighty stupid now, i forgot the ground wire between the tail resistor and the NFB resistor. Soldered it up and boom we have volume, and by volume i mean HOLY SWEET BALLS IS THIS THING LOUD. I am going to redo all my voltage checks this afternoon so I have a recorded baseline for future use, and then swap out my startup tubes for a fresh set and see how it sounds. Big thanks to Snfoilhat for leading me in the right direction, I would have been looking forever without your help.
     
  8. D'tar

    D'tar Friend of Leo's

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    Edit: Congrats on finding your issue! I was almost done typing when you posted!
     
    Last edited: Aug 5, 2019
  9. mefgames

    mefgames Tele-Afflicted

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    There's nothing like a happy ending !!!!
     
  10. Commodore 64

    Commodore 64 Friend of Leo's

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    Great troubleshooting boys. Have voltage chart, will travel!
     
  11. Clintstone

    Clintstone Tele-Meister

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    There's nothing quite like playing a Tele you built yourself through a Bassman head you built yourself into a 2x12 cab you built yourself. My wife snapped this pic after she heard me playing from in the house ( I think the neighbors heard me too haha ) the cab is a closed back with Celestion Seventy 80's in it. With the normal volume at about 8 and Frondelli master between 1 and 2 it sounds like a cranked up plexi, this is with the gain boost switch on. This might just be my new favorite amp. received_925885347761936.jpeg
     
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  12. Clintstone

    Clintstone Tele-Meister

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    Gettin some tolex glued on tonight 20190810_215737.jpg
     
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  13. Clintstone

    Clintstone Tele-Meister

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    Starting to look like an amp, I'm making the top removable so mods will be easy. 20190811_151948.jpg
     
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  14. Paul G.

    Paul G. Friend of Leo's

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    Some Traynors were like that. The chassis were bolted in from the sides, and the top of the head cab came off with 4 bolts. You could repair or service the amp in situ. Retube and rebias took a couple of minutes.

    It was just one of the ways they made them roadworthy.
     
  15. Clintstone

    Clintstone Tele-Meister

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    I'm not gonna lie, I completely stole that idea from Traynor. I have such respect for Pete Traynor, if everything in life was built like an old Traynor amp service technicians would probably swear less.
     
  16. Clintstone

    Clintstone Tele-Meister

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    Just need to fancy up the control panel a bit and it will be done, well done until I decide on the next mod to try. 20190816_204720.jpg
     
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