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My Voltages

Discussion in 'Shock Brother's DIY Amps' started by jh45gun, Apr 28, 2009.

  1. jh45gun

    jh45gun Banned

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    Sorry I confused you I said in the last post I will probably just leave it for what it is in other words not hotrod the 5e3 as I have my 5f4 build though that too is a bit different as it has a massive OT from a Peavey Amp that used 4 6l6s meaning I have that 5f4 for more power along with the bogen pa head project, though the 5f4 is a bit different too with that large OT. I guess I should not have talked about 3 amps in the same post to confuse the issue. Sorry. NOW back to the 5e3

    The OT for the 5e3 build is the stock Zenith OT that was on the chassis. I used both the PT and OT that were on the chassis since the origional zenith had all the same tubes except for a octal preamp tube a little less powerfull than a 12ax7 I think it ws a 6J5 if I remember right or something like that I swapped out that octal socket for a 9 pin socket to use the 12ay7.12ax7 the 5e3 calls for. Tubes are all OK they have all be checked and double checked. what could be the issue with the Input circuit??? that you may suspect???
     
  2. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    Did you wire them with 68k and one 1Meg resistors per channel, and did you wire them properly?

    If you wired the shorting jacks improperly you may only have a "Low" input with 68k instead of a "High" input with 34k (the two 68k's switched in-parallel at the switching jack).

    SO
    Is the input stock 5E3 with four jacks? Are the shorting jacks wired properly?

    ALSO
    Double check all of your resistors with a meter AND visually (reading the color bands). It may look like 68k and 1Meg, but in fact have the wrong multiplier band (and actually be 680k or 10k). Double check all resistors on the board too (not doubting Ken's work, but still).
     
  3. jh45gun

    jh45gun Banned

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    OK when I take it apart again the resistors on the jacks I know were one meg. Yes I have 4 inputs I put two in front of the amp and two in back because of no more room on the front of the chassis. I used the wireing diagram from one of the amp building sites for the input jacks.
     
  4. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    Measure the resistance from the High jack - you should have about 34k.

    Don't go from memory, try to actually measure the 68k input resistors AND the resistance of the High gain inputs (should be about 34k), and the V1 grid load resistor (should be 1 Meg).

    Its easy to see the color bands and think they're all good, but measuring them makes sure we didn't misread.

    If your input resistance is too much, you'll get A LOT less gain.
     
  5. jh45gun

    jh45gun Banned

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    Do you have to disconnect anything to take the resistance readings? Even if I drain the filter caps will there be any stray voltage stored in any of the caps that may screw up the meter?
     
  6. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    You can just measure the input circuit and avoid touching any hot spots (AKA, avoid shock hazards as usual - if you feel you need to drain the filter caps for this, then do so).

    Measuring grid resistors/input jack resistance isn't too complicated though.

    This might be your gain problem if the input jacks are wired incorrectly (a VERY common mistake on those three terminal shorting jacks).
     
  7. FiddlinJim

    FiddlinJim Tele-Holic

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    ... especially if you use the Weber (very nicely-drawn) layout diagrams. They were using a shorting jack with a different lug layout from the standard Switchcraft jacks. I learned that one the hard way.
     
  8. jh45gun

    jh45gun Banned

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    OK if this drawing is right this is how I did both of my amps my 5e3 and my 5f4

    [​IMG]
     
  9. jh45gun

    jh45gun Banned

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    SO I hope that is not the drawing that FiddlinJim was talking about.
     
  10. jh45gun

    jh45gun Banned

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    OK I took the amp out of its case again and I looked at the jacks they are hooked up like the drawing. The resistors on the board are 68K I should have taken a reading when I had the amp out and forgot. Now back together by putting a cord in the input jacks and taking a reading I do not get them numbers so more components have to be in play by doing that. Guess I will have to accept what this is it is I guess as every thing looks right to me as far as hooking things up. Wires a bit messy as you cannot lay them out like you would a regular chassis since this was made for something else the way it is laid out but the amp is as quiet as most amps and it does work just not like most 5e3's sound so you got me????
     
  11. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    Don't rely on drawings. What jacks are you using? Cliff style or Switchcraft style? Switchcraft you can easily see where each lug goes. Its pretty simple from there. Ground, live, and shorting tab (which you wire to ground right at the jack).

    The resistors on the board can still be 68k and you can still have gain issues IF the jacks are wired incorrectly. You should just measure them - its really not too big a deal to do.

    The input impedance/resistance has a direct effect on gain and if you really want to figure this thing out you need to eliminate or include it in the list of what is "wrong" with the amp. A 10w OT (wired for proper load/impedances) and stock 5E3 circuit does not explain why your amp doesn't act/sound like any other 5E3 on the planet. This isn't magic, voodoo, or mojo - this is plain science (not even science, just manufacturing tolerances).

    There is an explanation, you just need to find it. Measure it, or leave it as-is if you really like it.
     
  12. jh45gun

    jh45gun Banned

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    OK so where do you want me to measure? Like I said I put a cord in the jacks and measured the other side of the cord and just got weird readings so that does not work so evidently I have to take the amp out again which is no issue I will do it now but where do you want me to measure for the readings to make sure I am on the same page with you?
     
  13. jh45gun

    jh45gun Banned

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    OK I measured the resistors on the board all 4 measure 33.5 K so they are within tolerance.
     
  14. jh45gun

    jh45gun Banned

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    SO where do I measure at the jacks? They are switchcraft type Witm the meter set at the highest setting 2000K and putting a guitar cord in the jacks I get the following readings. channel using the first set of resistors on the board I get 134 on the jack with out the resistor and 962 with the jack with the resistor on it.

    This is for the second set of resistors on the board 1100 om the jack with no one meg resistor on in on the jack with the resistor the reading is 972
     
  15. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    Measure the input grid resistors the jacks feed. Put the meter probes on one side, the other probe on the other side of the resistor.

    Once you're sure they're 68k resistors. Then you double check your jack wiring.

    This should help (scroll down a tad):
    http://www.el34world.com/charts/CommonHookups.htm

    If the jacks are wired incorrectly, we can fix them and try that. If not, or it doesn't help, then we'll have to try to chase down what's wrong somewhere else. "Hotrodding" the amp for 6L6's will not increase gain, but instead do the opposite - make it louder and have more headroom.

    We'll figure it out... we just need to double check things and go over everything systematically.

    PS
    Have you tried a 12AX7 in V1? Does it make it crunchy/grindy, or is it still pretty clean up to 12?
     
  16. jh45gun

    jh45gun Banned

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    OK Johnny I did that as I stated before they read 33.5 K which makes sense as one side is joined together. I measured all 4 of them. I wired the jacks as this pic shows like I posted before.
    [​IMG]

    Yes I tried different tubes in VI they sound pretty much the same. Now this amp does have a bit of dirt dimed but not much for the most part it is pretty clean. No way does it sound like your clips or of the other clips I have heard.
     
  17. jh45gun

    jh45gun Banned

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    So Johnny what next?
     
  18. jh45gun

    jh45gun Banned

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    So Johnny take a look at the diagram I supplied this is what I followed when I built this amp. Does it look right to you?
     
  19. <jbc>

    <jbc> Tele-Holic

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    hey jh

    did you ever measure the input impedance of the OT?

    you can rig a quick-and-dirty signal generator by placing a guitar directly in front of the speaker so that it will feed back. bang the low E. then you can adjust the level of the signal with the guitar volume control. get a tone with constant volume going.

    if that works, then you can measure the AC volts at tp12, tp13, tp15, tp16 and tp17.

    with that information the situation with your amp should be clear.
     
    Last edited: May 3, 2009
  20. jh45gun

    jh45gun Banned

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    OK JBC thanks for posting that I will try that.
     
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