Help - A15 Mk2 no output

    Hello all
    Just completed the wire-up. Measured voltages etc. Plugged it in, valves glowed nicely. But while there is the quietest of hisses from the speaker I've connected, the jack input is totally dead. Needless to say, no signal from my guitar is getting through. My leads are pukka - so I must have have cocked up the wiring somewhere....
    Here is a link to some photos.
    http://s1130.photobucket.com/albums/m535/B0BB0/
    Any help or advice gratefully received.
    Cheers
    Robert

    Literacy as Social Practice

    Fuse burn out 0.2A on A15

    Hello all
    Got the amp working well. Fantastic range of tones.
    But then, the music died.
    The smaller of the fuses burned out.http://forum.musikding.de/vb/images/smilies/eek.gif
    I am now worried about where to start in terms of checking things.
    I suppose it might be the variable resistor that needs adjusting.
    Anyone had any experience of adjusting this or could give me some pointers
    as to what I should be checking?
    Thanks
    Roberto

    Literacy as Social Practice

    Hi
    would you like to open some other threads about this topic?:rolleyes:

    First replace the fuse (correct value! and buy a few of them :p), pull out the power tubes switch on and wait what happens.
    If the fuse doesn't blow measure all voltages (except the ones of the power tubes)
    Measure also the mains voltage (AC! V)when you do the other measurements.

    Bernd

    Jaichweiß (Andy Pipkin)

    By power tubes you mean valves 4, 5 & 6 right?
    Or do I pull them all out?
    I'm new to this and the learning curve has been quite steep, so excuse the basic questions!

    Literacy as Social Practice

    Hello Bernd
    OK, I'll check them. On the schematic it says "All voltages measured... at No-Load Conditions"
    Does that mean without the tubes, or without any guitar input?

    Literacy as Social Practice

    Hi Robert,

    "No load condition" is not a correct term - because that would mean "without speakers" for an amp (but you should never operate a tube amp without load).

    As you assumed "no input signal" is the right condition for measurements - but with the tubes plugged in.

    In your case you should omit only the two output tubes because the probability is high that there the raised current comes from...

    Bernd

    Jaichweiß (Andy Pipkin)

    Ok. Done it. There is clearly something wrong with output to bias resistor.
    readings were as follows:
    heater voltage: AC 7.66v
    Rectifier (+): 360v
    C26 (+): 324v
    Pin 2-3 of bias control = 0

    Feel like I am moving towards the source of the problem (thanks to your expertise and advice, of course!)
    Robert

    Literacy as Social Practice

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