Help: Problems replacing tubes on my Silver jube

Discussion in 'The Workbench' started by usablefiber, Oct 5, 2021.

  1. usablefiber

    usablefiber Active Member

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    My Silver jubilee 100 watt head reissue keeps having problems as does my yjm.

    It would power up fine. but when i put it off standby no sound sound come out. always double checked that the inputs and speaker outputs and all jacks and connections were in and solid but no sound.

    i looked in the back and the second power tube from the right looked much much dimmer than the others, barely even lighting up.

    i assumed it was just a bad tube so i replaced it with a matched quad of el34 after making sure to clean the sockets with an electrical contact cleaner, but even with the new quad the same 2nd tube is completely dim compared to the others. and again no sound after powering up.

    Is this a common problem or a potentially easy fix? if there is any kind of complicated repair needed to be done i’d have to take it to a tech which would suck, as 100 bucks for service would be s huge pain for me.

    Anyone have any tips? is this common or in some way a fixable problem at home?

    Thanks
     
  2. C-Grin

    C-Grin Well-Known Member

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    Have you eliminated everything but a guitar and cable? you say both amps are doing the same thing?
     
  3. Matthews Guitars

    Matthews Guitars Well-Known Member

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    Sounds like the amp needs to visit a qualified amp tech.
     
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  4. pedecamp

    pedecamp Well-Known Member

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    What do you mean "keeps having" has this been going on for a long time off and on? With both amps? Do you use the same guitar, guitar cable, cab cable, cab with both? Sounds like its something other than the amps, I'd start looking there.
     
    Last edited: Oct 5, 2021
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  5. Gunner64

    Gunner64 Emotional Support Animal Gold Supporting Member

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    Have you checked the h.t. fuse?
     
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  6. usablefiber

    usablefiber Active Member

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    I apologize i didn’t make this clear. the yjm has entirely different issues i forgot to mention that. but it seems to be working again for some reason now.

    And no it’s the amp because the exact same everything: cables speakers gear everything am using with the 800 and have had no problems with that amp for a long time now.
     
  7. usablefiber

    usablefiber Active Member

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    what is the HT fuse? that’s a different fuse altogether? and how do i check it?
     
  8. johan.b

    johan.b Well-Known Member

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    If you have the same problem with an other amp, perhaps your problem lays elsewhere...?.. speakers?.. cables?...
     
  9. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Uhh, it’s one amp, dudes.

    The ht fuse is the high voltage fuse. Many Marshall amps have 2 fuses. The tubes light up using AC controlled by the mains fuse but the b+ high voltage runs from the PT to the ht fuse before going to the tubes and board. So, it is possible that the tubes can light up and the amp still not work if the ht fuse is blown. Check your fuses with a continuity meter or by eye.

    2B0D3DFE-FFA7-4C9B-9F96-72EF601C910F.jpeg
     
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  10. Ken Underwood

    Ken Underwood Well-Known Member VIP Member

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    Judging by the replies from this guy then a good Tech needs to take a look at his amp, if not he is likely to kill him self

    A little knowledge is a dangerous thing
     
  11. Gunner64

    Gunner64 Emotional Support Animal Gold Supporting Member

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    Agreed. And you shouldn't just pop new power tubes in without biasing them. If you are unsure what the h.t. fuse is I 'm sure biasing is out of the question. I'm sorry but you do need a tech to take a look, like it or not.
     
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  12. pedecamp

    pedecamp Well-Known Member

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    Check ALL your fuses. Look at the back of the amp for fuse holders. If you replaced the power tubes dont forget to set the bias.
     
  13. Chris-in-LA

    Chris-in-LA Well-Known Member

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    All good points above but if he can change a tube, he can check a fuse. But, yes, it sounds like it’s time for a trip to a tech.
     
  14. johan.b

    johan.b Well-Known Member

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    ..."My Silver jubilee 100 watt head reissue keeps having problems as does my yjm."..

    ... i read that as two different amps with similar problems?....
     
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  15. Gunner64

    Gunner64 Emotional Support Animal Gold Supporting Member

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    Right, but at the same time if you don't know of the existence of the h.t. fuse you shouldn't be changing tubes I'm thinkin'. :)
     
  16. RLW59

    RLW59 Well-Known Member

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    There's probably two separate issues going on. The amp would still make sound if one if the power tubes wasn't heating up/not operating. In fact, except for some extra hum/noise you might not even notice it was running on only 3 power tubes.

    Did you check the preamp tubes by subbing in a known good tube one at a time into each socket? A dead preamp tube can cause an amp to not make any sound.
    ------------------------
    How brightly a tube glows varies from tube to tube. The glow is from the heater filament. What matters is if the heater gets hot enough for the tube to conduct current. Put the amp on standby for a minute or so and touch the dim tube and see if it's much cooler than the other 3. If it's hot it's fine, if it's cool it's probably a bad solder joint.

    If the preamp tubes all check out ok, all the fuses are ok, all the connectors are connected, and there are no visibly fried components, then it's time to take it to a tech.
     
  17. usablefiber

    usablefiber Active Member

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    Thanks guys for the tips! gonna grab some new pre amp tubes and try it.

    Also, i do know how to bias my jcm 800 sort of. i take it out of the box, put the tubes into my little reader display, and use a screwdriver on the blue little screwdriver thing until the bottom number gets to like between 38 and 40 i think it was i forget the exact number but i look it up whenever i have to.
     
  18. Gunner64

    Gunner64 Emotional Support Animal Gold Supporting Member

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    The jube reissue is a snap to bias, it has ports and pots right on the chassis with a little chart telling you the settings for various power tubes. All you need is a multimeter.

    Don't forget to check the h.t. fuse. No high voltage to the plates of the power tubes if that's blown..no high voltage=no sound.

    An easy way to check if the problem is in fact in the power amp section is to turn your guitars volume down and plug into the effects return jack, then power the amp up and raise the guitars volume slowly. If there isn't sound the problems in the power amp section. If there is sound your power amp section is working, and the problem is preamp related.
     
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  19. Lespaul 1958

    Lespaul 1958 New Member

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    On the YJM you can run the self biasing mode. It tells you how in the manual and even has a chart if you want the tubes to run cooler or hotter…. I have not touched the VR itself but recently changed power amp tubes (JJ) and ran the self biasing mode and it’s been awesome! It’s always been awesome… I gig with the yjm and get tons of compliments on the tone…. Getting off topic a little!
     
  20. usablefiber

    usablefiber Active Member

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    something went terriby wrong. so i put in all new preamp tubes. used electrical contact cleaner and put them in and out the sockets a few times as usual. my tech gave me a new fuse which i put in. made sure all the connections were good. 8 ohms into 8 ohms cabinet jack connection good all tubes cleaned and let 24 hours for cleaner to dry fully on. amp powers on. All tubes lighting up fine. flip the standby and immediately a huge popping sound comes on the speakers and i strum with no sound coming out. turn and off and it looks as if the new fuse immediately blew. I had the right fuse and tubes and everything i told my tech the amp model and everything.

    I’m so frustrated. i’m so tired of these amps constantly constantly not working and wasting hundreds of dollars going back to techs of money i don’t have to spend. i just want one of these two to last more than a few months before something blows up
     

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