More amp trouble - second SOS!

Discussion in 'Amps & Cabs' started by RVA, Nov 14, 2015.

  1. RVA

    RVA Well-Known Member

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    Thank you, but no worries. The amount I have learned on this journey is as valuable as the amp.
    Along those lines, I am now starting to see why this is not a more expensive amp. Am I correct that , similar to a switch, an amp with PCB boards and harnesses lacks the quality of an all "hard wired" point to point amp?
     
  2. chilipeppermaniac

    chilipeppermaniac Well-Known Member

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    Not necessarily, RVA. I am sure others may concur, there are likely many good quality PCB amps that have a good rep despite not being P2P
     
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  3. RVA

    RVA Well-Known Member

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    But the amp works other than the hum - BUT, when I fired it up briefly yesterday, there was a slight smell of hot plastic!
     
  4. chilipeppermaniac

    chilipeppermaniac Well-Known Member

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    Definitely not a good sign.
     
  5. 67plexi

    67plexi Well-Known Member

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    Like I said take voltage readings at the filament supply the large yellow wires your power transformer is going south.
    Or on a Highway to Hell. That smell is your insulation on the PT winding's burning.
    And the 5 watt sand cast 470 ohm resistors what was the ohm reading.
     
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  6. chilipeppermaniac

    chilipeppermaniac Well-Known Member

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    Pic of a Peavey Triumph 120 showing Trannies and Tubes etc.

    [​IMG]
     
  7. chilipeppermaniac

    chilipeppermaniac Well-Known Member

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    http://bmamps.com/Schematics/Peavey/Peavey_triumph 60-120 sch.pdf

    RVA, go here and scroll down to "power tube bd" for the 120, then zoom in to about 350%
    then look at the little circles and traces............

    I believe this is where 67plexi is trying to take you for the various pin areas to test the readings at V6,V7,V8,V9. Otherwise, a question for 67,,,, can RVA access test pin areas in the tube sockets with the 6L6 tubes pulled?

    67...... if this is not what you mean, or if you have further instructions, please add them here...

    PS, from your photos,,, I am not seeing as clearly as 67 may be able to see, but if somehow we could get a better view of the wires coming out of the Power Transformer,,,,,,,then some sense can be made on how to meter the Tranny to see what is going on unless that data can be gathered via the info I mentioned above
     
    Last edited: Jan 23, 2016
  8. chilipeppermaniac

    chilipeppermaniac Well-Known Member

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    Also, RVA, another member DFLCC knows about electronics and may be able to lend some input if you PM him and see if he is around to maybe check out your thread here. But I definitely think 67 is on to something, I just have to figure out how he wants you to test based on the layout your amp is built like.
     
  9. RVA

    RVA Well-Known Member

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    Chili, the video on testing a transfomer is super helpful. I believe the wires 67 refers to are the red, orange and yellow on the left in the overall view and depicted in part in closeups. I will put on my rubber shoes again and take some measurements !
     
  10. RVA

    RVA Well-Known Member

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    OK, so the readings are:

    Yellow wires: 0.2 ohms quickly falling off to 0.1 (this does not look good, right?)
    .03 AV
    .075 VAC


    Orange wires: 3.0 ohms on the outside leads, 1.5 ohms at the center tap to each side (thanks to chili's video, I know what a center tap is!)
    .02 AC
    .01 VAC


    Red wires: 11.1 ohms on the outside leads and 5.3 ohms and 5.7 ohms on the middle tap to alternate outside leads. I am not sure why it has a combined higher reading, but I am guessing that this is the bias tap (again, thanks chili!). This amp does not have a bias adjustment.
    .082 VAC
    .13 AC

    So, where does this leave me? I am guessing it is time to start hunting for a replacement transformer!
     
    Last edited: Jan 23, 2016
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  11. chilipeppermaniac

    chilipeppermaniac Well-Known Member

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    I am awaiting with lots of anticipation to see what 67 or others say based on this.
     
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  12. RVA

    RVA Well-Known Member

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    I have not had the easiest time hunting down a possible replacement. Looks like the 5150 transformer may be suitable...available from Mercury (ugh!)
     
  13. chilipeppermaniac

    chilipeppermaniac Well-Known Member

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    RVA, Mercury makes the great trannies.
    Also you may check out Brian Wallace at Marstran. That is where I got my JMP tranny from.
    You could also ask him about rewinding your Peavey one to see if he can do that for you.

    http://www.marstran.com/Index.htm

    Also, don't forget, there is a reason for the tranny failure if it has indeed gone bad. You must find the cause or you will highly likely to be replacing another trans.
     
    Last edited: Jan 23, 2016
  14. RVA

    RVA Well-Known Member

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    I found BOTH trannies for sale on ebay for $ 130. The seller verified the model #. Should I grab them?
     
  15. 67plexi

    67plexi Well-Known Member

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    Test the yellow wires in the amp power on AC volts should read 6.4 + volts AC. You can test where the yellow wires plug into the board.
    In the last few months had shorted tube take out the PT in a Fender Twin Reverb same low reading on the filament 4.2 VAC
    HUM and the wonderful burnt smell.
     

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  16. RVA

    RVA Well-Known Member

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    The yellow wires read .03 AC / .075 VAC (see all measurements posted above). Thanks.
     
  17. 67plexi

    67plexi Well-Known Member

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    My input voltage is only 117 VAC if it was 120-125 VAC it would read higher on the secondary yellow wires than 5.59 VAC
     

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  18. RVA

    RVA Well-Known Member

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    So what does that indicate? i just double checked the readings and they are consistent.
     
    Last edited: Jan 23, 2016
  19. 67plexi

    67plexi Well-Known Member

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    RVA if that is your true readings the power transformer is toast. If you love that amp save up for a good used one.
    The reason it could be more wrong with that amp just changing parts does not fix a amp.
    When I get a repair amp on my bench I voltage chart the complete amp then test all resistors and capacitors and transformers test the tubes.
    When I build a amp that is a whole different dimension once I have the voltages blueprinted then I adjust the current flow and frequency response.

    Good luck, Steve.
     
  20. 67plexi

    67plexi Well-Known Member

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