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Blowing fuses on startup?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by Stranks, Apr 28, 2005.

  1. Stranks

    Stranks Supporting Member

    Messages:
    114
    Joined:
    Feb 9, 2002
    Location:
    Stamford, CT
    Hi all!

    I stupidly tried a solid state rectifier in my Twinmaster and immediatly blew the fuse upon taking the amp off standby. The panel indicated a 1.6amp, 250v, T-type fuse replacement. My local Radio Shack had everything but the "T" (but said slow-blow). The only difference I could see was that the wire going through the cylinder was smaller. The original one had a wire like a wound D string wereas the new one is the size of a high E string. Not everytime but maybe every other I blow a fuse upon powering up. I spoke with Jeff Bober at Budda and he said to try removing the power tubes and trying it (it was OK) Then the rectifier. It seemed to be OK without those in place. Just to be sure I ordered new power and rectifier tubes, popped them in and I'm still blowing.

    Do I need to source out a fuse with the beefier wire? If so, where can I get them from Online?

    I appreciate any help!!!!!

    Thanks
    Brian Steranka
     
  2. John Phillips

    John Phillips Member

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    Mar 17, 2002
    Location:
    Scotland
    It's hopefully just the fuses - but there is a small chance that you've done some other damage, possibly to a filter cap, with the increased voltage from the SS rectifier.

    I have a nasty suspicion that it might be something like that, since the wrong mains fuse type will usually blow on power-up, not when taking the amp off standby. A blown fuse on switching the standby to on usually indicates a fault in the HT circuit - or tubes, but you've eliminated those...

    Hope I'm wrong - maybe worth another call to Jeff, he'll be able to tell you whether this is even a possibility from the component ratings in the amp.
     
  3. khudson

    khudson Member

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    Aug 27, 2004
    Location:
    North Carolina
    If you re-installed your rectifier tube (assuming the tube isn't bad) and it still blows, chances your amp will need repair. I have a Germino and the fuses kept blowing on me too when taking the amp off standby as John mentioned. I went to Radio Shack and kept replacing the fuses. Come to find out it, my rectifier tube was going bad. Replaced it and no problems since. As long as the fuses are the same amperage as required, I wouldn't lay too much blame on them, but start troubleshooting elsewhere.
     
  4. Stranks

    Stranks Supporting Member

    Messages:
    114
    Joined:
    Feb 9, 2002
    Location:
    Stamford, CT
    Thanks guys but I don't think I explained correctly. When I meant start-up, I meant to say power-on (first action), standby still on. When I do get the amp on (without blowing a fuse) and take it off standby it never blows at that point.

    ???????

    Brian
     
  5. John Phillips

    John Phillips Member

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    Mar 17, 2002
    Location:
    Scotland
    That does sound like the wrong type of fuses.

    The standby terminology can be confusing... "standby on" means the amp fully operational, not the "amp on standby", to me. Now I've re-read your first post, it's obvious... :)

    The best type of fuses for amps are the T type with the coiled 'spring' inside - they have the highest short-term-surge rating compared to their actual blow value.

    I really wish more amp makers would fit proper separate fusing for power and HT circuits though - some, like Marshall, have always done so - it makes problem tracing like this far easier than just relying on a single mains fuse, and protects the amp better too. That way you can use a slightly less over-sensitive mains fuse value, since it's there to cover only for major shorts in the PT or filament circuit.
     
  6. Stranks

    Stranks Supporting Member

    Messages:
    114
    Joined:
    Feb 9, 2002
    Location:
    Stamford, CT
    Thanks a bunch John!!!

    I will now try and locate the T type I need.

    Brian Steranka
     

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