Vibro Champ heater wires

Discussion in 'Amp Tech Center' started by tele_savales, Jun 10, 2019.

  1. tele_savales

    tele_savales Tele-Meister

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    I've done a bunch of work on this little VC I got. Replaced the filter cap, electrolytic and tone caps, swapped out a noisy preamp tube, put a new Tung-sol 6v6 in, tightened the pin sockets and loose power switch, cleaned all the pots and jacks, clipped the death cap, re-flowed some solder joints and detailed the cab including gluing down tolex and so forth. I'm waiting on a couple larger resistors to cool the bias a bit. I am highly stoked on the work light I got off Amazon and feel like a half-blind moron for not getting on 2 years ago. It's really nice!

    It sounds quite a bit better and I didn't even burn the building down. Most of the weirder sounds are gone except a pronounced hum. I am planning on adding a virtual center tap and flying tightly twisted wires to the filaments. The question I have about that is should I clip the ground wire at pin 9 on the preamp tubes and pin 7 on the power tube once they're wired directly? I've compared lots of schematics and diagrams and they are rarely in agreement.

    Also, I am probably going to remove the added speaker jack in favor of a tone stack lift switch and replace the speaker and baffle at some point.

    First pic is right before removing the cap can. after.JPG clamps.JPG b.JPG d.JPG
     
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  2. galaxiex

    galaxiex Tele-Holic Silver Supporter

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    Yes, if you are going to wire the heaters direct you need to clip those grounds.

    It's one OR the other, never both. Ie: one side grounded OR both wired direct.

    FWIW, are you sure the heaters are the source of the hum?

    I went through this on another small amp recently,
    spent some time and effort to wire the heaters direct, getting rid of the "one side grounded" scheme...

    ... and it made not one iota of difference in the hum level.

    Suggest "chop sticking" the wires and moving things around first, before re-wiring the heaters.
     
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  3. dan40

    dan40 Tele-Afflicted Silver Supporter

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    It is a single ended amp so getting rid of all of the hum may be difficult. Upping the main filter cap value does help but with a 5y3, you can only go up so far. I have run them at 40uf with no ill effects on the rectifier. A good quiet tube in v1 is also helpful.
     
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  4. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Do you know the frequency of the hum? How bad is "pronounced" ? Loud enough to still show up during playing?
     
  5. tele_savales

    tele_savales Tele-Meister

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    After the recap and startup I poked around a bit and found v1 socket to be a little noisy and loose. I had a couple old Marshall branded ecc83's laying around and the 3rd one I tried was substantially better, although they are probably original stock to my 2005 plexi RI, and not necessarily "known good".

    There's a lot of wax on the board, the wires from the cap can were real loose, with broken strands, and oxidised, not looking like they were tinned before being soldered, so I have some replacement wire coming and I'll go thru every single connection, and replace anything I don't like. I also need to re-flow all the pin connections. My time was limited and I wanted to play thru it a bit, which I did for maybe 15 minutes, so I buttoned it up till next weekend.

    As far as the noise, it's angry bees in your face once the volume is at about 5, not really playable. Definitely a bit more than good old fashioned tube amp noise.

    Since I already bought the caps and did the work I'd rather try something else before changing those values. If I throw money down for more caps I have to do my Plexi. There has been a huge difference since swapping those components and i think with a little more work I'll be golden. All suggestions are super appreciated.
     
  6. BigDaddy23

    BigDaddy23 Tele-Meister

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    Re- doing the heaters with the artificial center tap is a good idea. You will need to remove those pin 9 grounds.
     
  7. Wyatt

    Wyatt Tele-Afflicted

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    Yes. The old small Fenders were wired with unbalanced heaters to save time, cost and space. Since you'll be wiring it up with balanced heater, those grounds go away. Unbalanced heater have the potential for added hum, but in low-gain circuits like these, it rarely happens. All old Champs and many small Tweeds had unbalanced heaters with no issues. If you're getting a lot of hum, I'm guessing its' from somewhere else.

    Since this amp is cathode-biased, run your 100R resistors from pins 2 and 7 on the 6V6GT to pin 8 on the 6V6GT, this will DC elevate the heater ground.

    The line out (it is a ,line out, correct?) running across most of the grid wires seems suspect.
     
  8. Silverface

    Silverface Poster Extraordinaire Ad Free Member

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    Check your lead dress as well and make sure no signal wires run parallel to high-voltage wires. They should be apart and when they cross try to make it at as close to a 90-degree angle as possible.

    In these amps, as mentioned earlier, a small wire movement can have a big effect on hum - even 1/4"! So poke around and lift/shift everything (even if you think it's irrelevant) - you may be surprised.

    And where DID you put the filter caps? They're not visible and it appears you bypassed the "can".
     
  9. tele_savales

    tele_savales Tele-Meister

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    Thanks! I put in a CE can to replace the original. In the pic I had just unsoldered the wires and found out I needed a blowtorch to loosen the chassis grounds.
     
  10. tele_savales

    tele_savales Tele-Meister

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    Yeah,
    Yes its wired of the rca jack. I feel like I want it gone. It's not original, its in the way, and my whole endeavor is to have a small amp. I have other things I can use with extension cabs. It's definitely in the way of flying the heater wires. So would there be any issue running the resistors on the power tube with the grid to cathode cap that's there? What are the benefits of doing it on the tube as opposed to the pilot light? Thanks.
     
  11. Dacious

    Dacious Poster Extraordinaire

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    Had two VCs - dead silent. I don't think it's your chassis grounded heaters.

    Replacing all the non-electrolytic caps probably wasn't necessary. Nothing wrong with the originals in most cases but no foul.
     
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  12. tele_savales

    tele_savales Tele-Meister

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    True. They were fine.
     
  13. galaxiex

    galaxiex Tele-Holic Silver Supporter

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    Yup, my early 70's VC with chassis grounded heaters is dead quiet too.
     
  14. tele_savales

    tele_savales Tele-Meister

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    If everybody thinks it isn't the heater wires, any further ideas as to what it is?
     
  15. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    "angry bees" doesn't sound like hum. Do you have a recording? Or a clip online that is similar?

    Does the sound change with volume or tone adjustments? Did removing the line out stuff change things?
     
  16. tele_savales

    tele_savales Tele-Meister

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    It gets louder as volume increases, changing the treble and bass modulate it accordingly but it doesn't go away. I'll post a clip tomorrow, too late to turn it on even without a signal running thru it. I haven't removed the output mod yet.
     
  17. LudwigvonBirk

    LudwigvonBirk Tele-Holic

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    Based on some thoughts shared in another thread, I just in the last couple of weeks carefully stapled some thin sheet steel to the inside top of two different Princeton Reverb cabinets (self-build circuits) and in both cases it appears to have entirely fixed a nasty hum I had been having at higher volumes at a weekly cafe gig (old house wiring, lights on dimmers). Faraday cage- it helps.

    (*My Silverface PR doesn't have the cabinet shielding and doesn't have the hum at that same gig spot, same plug. Idk why not. I guess I could drag in the amp and a scope and order a plate of felafel and start sawing away on a restaurant table...but there aren't enough unallocated hours in my day, currently.)
     
  18. tele_savales

    tele_savales Tele-Meister

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    Here you go. The work lamp over it is unplugged.



    Also, LudwigVB, I had the same thought when the chassis was out on the bench, but there's factory shielding inside the cabinet and it didn't change the buzzing much when I put it back in.
     
  19. Wyatt

    Wyatt Tele-Afflicted

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    I had to crank my volume to hear that, unless the video volume is lower than in real life, it doesn't seem like an unnaturally loud hum with everything cranked. With a guitar at that volume, you can drive most people out of a large house.

    Are your jacks properly shunting the tip to ground when unused?

    Any florescent lighting? LED household bulbs? Any digital devices in proximity?
     
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  20. corliss1

    corliss1 Friend of Leo's Platinum Supporter

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    Sounds like normal amp to me, although it's hard to tell the volume over a video without some other noise for reference. I generally expect noises to happen like that when any amp is cranked.

    It is loud enough to interfere with playing?
     
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