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Thread: Ampeg VL-503 not working tube arent glowing

  1. #1
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    Ampeg VL-503 not working tube arent glowing

    I just got this VL-503, the thing worked when I checked it out, but when I got it a home and cleaned it up pots and so forth. When I got it back together Its not working. There is no sound and not a one of the tubes are glowing. I will admit that I hit one of the power tube with a screw driver on accident, do you think that this could be the problem? Can a tube go bad so that it wouldn't emit light? and If one power tube isn't working would the other not light as well, or should I look else were? I'm about 85% sure that I got every thing back in the right spot, This isn't my first rodeo. I'm lead to believe that the tube where in need of changing to begin with. any ideas would help.

  2. #2
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    Well I figured it out there was a loose wire from the tranny.

  3. #3
    Senior Member Guitarist's Avatar
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    Very nice amp! Some of them had an issue with the filament wiring getting hot and melting the molex connector. Clean or solder on perhaps. I just shaved off the last two or four wires from the rest. I've did some serious mods to the VL102, or whatever it was called.
    Did I say killer amp!

  4. #4
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    I have fell in love, Now that its working. By far one of the best sounding amplifiers I have owned to date. What where the mods you did. If anyone else has any mods or a schematic that would be real cool.

  5. #5
    Senior Member Guitarist's Avatar
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    N.B. This applied to the the VL- 502 and good tonal gains were realized, according to my taste. Still, doing this to my amp, well designed and constructed it really is, made me a believer in point-to-point.

    Approach: move gain/volume downstream and defrag front-end; Improve clean tone

    1) Swap both volume pots of clean channel preamp away from 1M < -- > Master 250K
    2) Move C3 to now parallel r9 of V2a (worry not, tone sections still moves mucho bass). Cap can be decreased to 5uF
    3) Increase sizes of clean caps C2 (interrupt trace) and C7 to .047
    4) Remove R11
    5) Increase R5 to 220K
    6) Try a feedback circuit 40M in series with a big cap such as .1 from plate to grid of stage 2/V1b. Optional
    7) Parallel R10 with a 150K resistor. This is to optimize the tone of the lower mu triode. Optional
    8) Change V2 to a 12DW7 (dirty channel's triode/half still high mu) or a 12aT7 etc.
    9) Parallel C1 with a 1uF. (This will fatten up the heavy channel as well)
    10) Increase trebel tone cap to 500pF. Optional.

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