JTM45 RI no sound... Freaking out

Discussion in 'The Workbench' started by Terry Cooper, Nov 24, 2021.

  1. Terry Cooper

    Terry Cooper Member Silver Supporting Member

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    The filament does look broken in a tiny spot right in the middle I mean there's no major break you know big black burned looking brake I'm on my way to my shop right now to get a meter so I can check it but on the standby switch I use mine a lot so I did not know that had no idea so thank you very much I definitely just learned something but yes I use mine quite often will post soon as I check continuity through this fuse
     
  2. StingRay85

    StingRay85 Well-Known Member

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    I think what probably triggered Mr. Underwood was his statement about Marshall copying the Bassman :D

    I wonder who "invented" the cascaded channel of the 2203/2204. Wasn't it Mesa Boogie that came up with the cascaded gain channels? I know they sued Acoustic Control Corp over this, and basically ruined that company.
     
  3. eastsidecincy

    eastsidecincy Well-Known Member

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    I have blown a fuse when turning on my 79 50watt Marshall too....never leave it on stand-by anymore....I thought a tube was blown but it was a fuse...:jam:
     
  4. Terry Cooper

    Terry Cooper Member Silver Supporting Member

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    Ok,fuse is definitely blown,no continuity,so should I try to just replace the fuse and if so what should I replace it with? what I mean by that is if I want to try to find something locally what would be the equivalent say from a hardware store or is that even an option? I mean I'm capable I'm just unexperienced working on amps.
     
  5. Dblgun

    Dblgun Well-Known Member

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    If it is the HT fuse it should be a 500mA. Your other fuse will depend on your primary. If you have the amp powered with 110-120vac then it will typically be 3A and 220-240vac typically 2A. There are always some exceptions but the above is what I have seen for the most part. Make certain that you get the right fuse.Thesse can be difficult to locate at a hardware in some cases.

    Before you replace the fuse(s) you need to determine why the fuse opened. As Neil mentioned previously a failed power or rectifier tube could be to blame among other things. It needs to be sorted out before you replace the fuse and power it again.

    You seem willing to learn to make these types of repairs but might be best getting a little help on this one as there is potential of harm to both you and your nice amp. You will certainly get help here but need to consider how comfortable you are with where you are at currently. Hope you get it back up and rocking soon.
     
  6. Terry Cooper

    Terry Cooper Member Silver Supporting Member

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    Well here's where I am,I did industrial electrical work for years...Mostly on the front end, installation....running cable tray, conduit pulling wire. Toward the end I started to get into the low voltage control wiring, even some basic ladder logic training, so as I said, I'm capable, just un experienced with this type trouble shooting. I can read prints, follow schematics.... I just need a little direction on where to start. I don't feel like anyone here would purposely leed me in the wrong direction, that may be a little naive on my part but I don't think so...., That being said I'm sure that y'all are busy and have things to do also so it's just a matter of if someone has the time to give me that direction then it would be greatly appreciated.. and I'm in the states so we're definitely on the the 120 volt I'm actually around Knoxville Tennessee
     
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  7. Dblgun

    Dblgun Well-Known Member

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    Fair enough, you're in the right place. There are some very helpful and knowledgable folks here.

    I would start by getting the chassis out of the cab/shell and get it somewhere you can get a good look. You obviously need to look for something obvious, broken connections, heat damaged components or wiring, etc. Look over the tubes for obvious signs of overheat and/or arching. Take some good quality detailed photos of the amp and post them here so folks can also get a look.
     
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  8. Kelia

    Kelia Well-Known Member

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    This happened to me two weeks ago and it was the Rectifier that went sour ,
    changed it , put back the fuse and all good to go. Hopefully you'll have the same easy fix.
     
    Last edited: Nov 25, 2021
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  9. Chris-in-LA

    Chris-in-LA Well-Known Member

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    That squealing sound! I had a 5e3 build that I was working on the squealed badly when I put it into standby. I fixed it by removing the standby, just has an off and on now. Glad to find out what the squeal was and that the amp is better off without the standby.
     
  10. Terry Cooper

    Terry Cooper Member Silver Supporting Member

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    Okay awesome, obviously it may be tomorrow afternoon before I can actually get it out of the shell and and start all that but by Friday morning I will definitely have some pictures posted and kind of go from there thank you very much to any and all that would help me out here I really appreciate it I do
     
  11. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Got the schematic? Google for a Marshall 2245 schematic. You'll find it easily enough.
     
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  12. Terry Cooper

    Terry Cooper Member Silver Supporting Member

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  13. Ken Underwood

    Ken Underwood Well-Known Member VIP Member

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    Before i blow a fuse lol then FFS stop calling me Mr Underwood, Ken is my name on here and i don't need any politeness because of my background, i have said this before, so don't piss me off again
     
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  14. Pete Farrington

    Pete Farrington Well-Known Member

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    I think it’s really beneficial for valve amp owners to have a light bulb limiter (and incandescent bulbs of various wattage ratings) for these scenarios, ie fuse blows but exact fault is unknown.
    Is the problem due to a bad rectifier valve, bad output valve, bad something else, or was it just a spurious blown fuse?
    The light bulb saves blowing a bag of fuses as those potential faults are worked through and eliminated, provides a visual good / bad indication, and most importantly, protects the amp from repeated exposure to fault current incidents.
     
    Last edited: Nov 25, 2021
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  15. StingRay85

    StingRay85 Well-Known Member

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    Noted, Ken.

    I don't want to be responsible for you blowing your mains fuse :thumb:
     
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  16. Ken Underwood

    Ken Underwood Well-Known Member VIP Member

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    Blew one years ago but mended the problem and don't want to go there again.

    I just don't want to be put on a Pedi stool for something i was involved in 58 years ago that now is a massive brand name, sadly that it all it is today a brand name.
     
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  17. StingRay85

    StingRay85 Well-Known Member

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    Sure.

    So to bring things back on topic, the only point of the standby switch is to change instruments, and not to warm up the tubes in advance (which would be a bad thing)?
     
  18. Ken Underwood

    Ken Underwood Well-Known Member VIP Member

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    Beg to differ, so were has you info come from? as this is some thing we discussed in length, originally it was the reverse of what you have said.

    Dont forget we are talking about 1963 and very few, if any bands, had more than one instrument to play with, things today are quite different of course.
     
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  19. Pete Farrington

    Pete Farrington Well-Known Member

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    For the receiving type valves we use, it only takes about 30-45 seconds from heater power being applied for the cathode to have been heated to operational temp.
    From the perspective of the valves, in the case of solid state or directly heated valve rectification, I’m not aware of any technical reason why HT voltage shouldn’t be applied whilst that’s happening.

    Of course for those few seconds, the HT voltage will rise to its peak / unloaded level, and if the HT caps haven’t got sufficient voltage rating to accommodate that, a standby switch and its accompanying ritual may be a good idea.

    Lots of players seem to like standby as a convenient muting switch, but pulling the plug 1/2” out of amp’s input jack does that too.
     
    Last edited: Nov 25, 2021
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  20. Terry Cooper

    Terry Cooper Member Silver Supporting Member

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    I just don't want to be put on a Pedi stool for something i was involved in 58 years ago that now is a massive brand name, sadly that it all it is today a brand name.[/QUOTE]


    Ok now I gotta ask,what company were you affiliated with?
     

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