Doh! My 1974X went down last night...help?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by rockinlespaul, Jun 29, 2008.

  1. rockinlespaul

    rockinlespaul Member

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    Well I was just playing my 1974X last night and all of a sudden, nothing....

    I looked over and both the stanby and power light was off. Wut wo....

    I shut both off, pulled the plug from the wall and took a look in the back at the fuses first. There are two seperate fuses...HT Fuse and Mains Fuse. The HT looked fine, and was not blown, however the Mains fuse appears to be blown. Nothing but glass, no type of center wire, etc....

    What would make this happen? Also...it says right on the back panel the type of fuses this takes but the print is too small for me to read. Anyone know the proper fuses for a 1974X?

    The only thing I've done to this amp since I bought it is that I retubed it a few weeks ago with new Mullards across the board and a EH in the rectifier slot.

    Any suggestions what may have happened? Hopefully I can get the proper fuse today and fire her back up. Thanks fella's...
     
  2. Blue Strat

    Blue Strat Member

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    Can't remember if that amp uses a tube rectifier or not. If it does, that would be the first place I'd look.

    Always suspect the last thing that was changed, in this case...tubes.

    Power tubes typically take out the HT fuse rather than the main fuse. Sometimes it's impossible to tell from looking at a fuse whether it's blown or not. Try a multimeter to be sure.
     
  3. rockinlespaul

    rockinlespaul Member

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    It has a EZ81 rectifier tube. I replaced all the tubes with current RI Mullards except the rect. tube which was replaced using a EH.
     
  4. phsyconoodler

    phsyconoodler Member

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    Mains fuses blow for a number of reasons,but I suspect the rectifier tube.
    Thje last thing done is always suspect.
     
  5. rockinlespaul

    rockinlespaul Member

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    Thanks...yes I'm thinking it may be too. First I need to find the right mains fuses. Anyone know? I can't read the damn small print...grrrr..:FM
     
  6. JJman

    JJman Member

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    Every main fuse I've seen on a 117v guitar amp was 2amp slow blow. Of course there are others but that seems to be the most common and would blow only when the entire amp consumes more than ~240watts (in the USA.)
     
  7. jay42

    jay42 Member

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    It has to be at least 1.5A. 1A SB's wouldn't last for me.
     
  8. rockinlespaul

    rockinlespaul Member

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    I'll get a magnifier to see. I appreciate the help, but I'd like it to be the exact correct fuse. Thanks guys.
     
  9. Structo

    Structo Member

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    Did you rebias after the tube replacement?
     
  10. rockinlespaul

    rockinlespaul Member

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    No, there's no need to rebias a 1974X.
     
  11. PeeWee

    PeeWee Member

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    Sounds to me that you've experienced the dreaded tranny meltdown that these amps are known for. Happened to me a year ago. If it continues to blow fuses, it's your OT. The stock Dagnall trannies are severly underpowered and can't take being run at the volumes that produce that classic Marshall tone - say between 7 and 9 - for extended periods of time.

    Do yourself a world of good and get in touch with the guys at Mercury Magnetics. Paul Petronete was a tremendous help and gave me recommendations that not only added better trannies, but improved the overall tone of the amp 100%. The amp now sounds as good or better than a lot of the original 1974s I've heard.

    One warning though - it's going to cost you to repair the amp. I spent nearly $700 in parts and labor getting mine back into gigging shape....and the amp was only 6 months old when it went down.
     
  12. Blue Strat

    Blue Strat Member

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    Yow! Now THAT's revolting!!
     
  13. mrmojorisin

    mrmojorisin Member

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    Always, always assume the problem is teh tubes until you concretely verify otherwise, as 99% of the time it is the tubes.

    The quality of new production tubes blows IMHO. Its not unusual to have them die shortly after you pop them in.

    My guess is that either the rectifier tube or one of the power tubes fried out.

    In fact I'd bet money on it :)
     
  14. rockinlespaul

    rockinlespaul Member

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    I hear ya....thanks guys.
     
  15. The Pup

    The Pup Supporting Member

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  16. rockinlespaul

    rockinlespaul Member

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    Yeah, I was looking at their site earlier. $250.00 for the "fat stack" tranny. Ouch...I'm hoping for the best too, lol.

    What about Drake transformers? Do they make anything for the 18 watter, if it is in fact the tranny that went?
     
  17. teleamp

    teleamp Senior Member

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    Heyboer make a great PT for the 18 watter, Mojo sells them at a decent price.
     
  18. rockinlespaul

    rockinlespaul Member

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    I was on that site earlier also. They did not mention a brand name for the two they had. One was 60 some odd dollars, the other was 90 bucks.
     
  19. mrmojorisin

    mrmojorisin Member

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    I'd go with the Herboer. The MM sounds more hi fi and less vintage to my ears. Besides that it is ridiculously overpriced IMHO. You'll be really happy with the Heyboer.

    But then again I am pretty sure your OT ISNT fried.

    And if it was I am sure you could get Marshall to replace, or at least send you a replacement for your tech to install, for free, esp if there are known issues with teh OT in the `1974x.
     
  20. The Pup

    The Pup Supporting Member

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    I've only done three of these and found that I liked the MM iron better...essentially discovering the opposite finding.

    I also have used the Vox 30 Woden Heyboer clone and it's frequency response is far greater (HiFi) than the MM variant...easily fixed with a few caps and a resistor.

    I think Heyboer and MM make some of the best iron today. The Heyboer is far more competitively priced too.
     

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