Can you diagnose this squeal for me (5e3 build)

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by jh45gun, Jan 23, 2008.


  1. jh45gun

    jh45gun Member

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    Well happy with my 5e3 build out of my zenith chassis and loaded turret board from Ken at Watts. Except one little issue if I turn on the volume on volume two with nothing plugged into it it gets a high pitched squeal as you turn it up. IF you plug a guitar in it then it works fine. Got any ideas? I used switching jacks and did put a 1 meg to ground on both of them. Other wise the amp works fine and I was glad to see that after fireing up after putting it together. No glowing tubes or smoke was a good thing :BEER
     
  2. jh45gun

    jh45gun Member

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    Another thing I am pretty sure I wired the pots right as I double checked the digagram and set the chassis on its end so I could see the pots with the terminals in an upright position. Is this amp a bass cut or treble cut on the tone control as it seems I have treble when the tone is at 0 or 1 and as I turn it up to ten I get more bass.????
     
  3. 67super

    67super Supporting Member

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    Sometimes the switching input jacks don't make contact. When you plug your guitar in your fine but when nothing is in the 1 meg connection to ground isn't there do to the faulty jack.
     
  4. jh45gun

    jh45gun Member

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    it looks like it is making a connection. I am wondering more now about that tone pot if that is the culprit and I have it wrong some how as the treble is more pronounced at the 0 to 1, 2 range then the ten setting?
     
  5. Trout

    Trout Member

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    Reverse the primary leads on the output transformer. That is a very common issue.

    Trout
     
  6. jh45gun

    jh45gun Member

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    Thanks Trout that did it now all I got to figure out is why the tone pot seems backwards ?
     
  7. Londoncalling

    Londoncalling Member

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    Gotta love The Gear Page!
     
  8. Bob Arbogast

    Bob Arbogast Supporting Member

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    That's a common issue with amps that employ negative feedback from the output stage, which a 5E3 does not. If switching OT primary leads fixed the problem, then there is still a latent problem left somewhere in the circuit/layout. The backwards working tone pot is one indication that all is not well.

    Bob Arbogast
     
  9. jh45gun

    jh45gun Member

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    Bob Since I am using a chassis that was a Zenith mon0 amp it in its former life did have negative feed back so maybe that is why changing the leads helped. As far as the backwards working tone pot I am not sure whats with that unless I did it backwards though I do not think I did as the vol pots work as intended.
     
  10. jh45gun

    jh45gun Member

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    OK John here is a couple of pics but they will not help ya much as since this was not a 5e3 chassis and is a made into a head cofiguration the wireing is going to be different then the way it goes on a normal 5e3 chassis. Now I know you guys know more than I do but since Trout knows this is a 5e3 build there must be a reason he told me to change the OT leads around????

    [​IMG]

    [​IMG]
     
  11. Swarty

    Swarty Member

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    If it were a NFB issue I'd expect it to act up with a guitar plugged in and possibly not act up with nothing plugged in. I suspect the issue is at the input.
     
  12. Trout

    Trout Member

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    In This picture, The Mica Cap and the yellow .005 film cap are reversed.
    So basically you need to rewire the tone pot correctly.

    Look at the layout here, You simply reversed the capacitors, Its pretty easy to do, .005(yellow) Vs .0005(500pf)(brown mica)

    [​IMG]

    Enjoy!
     
  13. Trout

    Trout Member

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    This might not be a constructive solution, but hey, These builds are basically a learning experience so here is a thought.

    I realize the build is sort of working, but as John has pointed out, there are still lead issues, both length and dress. If you want to get it sounding and working as close as possible to a 5E3, getting it straightened out a bit more will help a lot.

    Food for thought,

    If you sort of start over, you can actually eliminate some of them by removing the board and mounting all the components on the opposite side of the board.

    Then re-mount the board, The components will remain upright like in your pictures, but all the connection points will be on the correct sides of the chassis in relationship to the sockets jacks and pots. Of course pay close attention to cap polarity.

    I can see where the trouble really started in your original post, Buying the board already populated with parts. Those were set up for a standard Fender style chassis, once you switch to a head stylechassis, everything flipped front to rear.

    It will take a good deal of care to desolder everything, and it might be easier to just replace some of the parts, but hey there is only a few bucks involved.


    Anyway, thats some food for thought, not exactly 100% constructive, but you could always look at it like your starting a second build.
     
  14. jh45gun

    jh45gun Member

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    Thanks guys I am going to try switching the tone control caps first.
     
  15. jh45gun

    jh45gun Member

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    OK that did it the tone pot is working fine now and the amp sounds good so I am not going to bother with changing any leads and maybe causeing me some grief doing it as long as the amp sounds good. It has good sound to it so I am happy. I compared it to my Silvertone 1472 and it sounds real good so I am happy with it.
     
  16. jh45gun

    jh45gun Member

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    I think I need to get another 12ax7 to try and I called my tech and said I would come over in week or so and try a 12ay7 in V1 and an other 12ax7 so the amp is running two of them as I have now to see what I like the best. I switched both 12ax7 tubes to see if it made a difference and the tube I had in the V2 cuts the volume down if I put it in the V1 socket so I am guessing that tube is weak even though it checks out ok. If I put the tubes back as I origionally had them the amp gain comes back to good again
     

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