Marshall 6101lm Anniversary Series - Preamp Issue

Discussion in 'Marshall Amps' started by Thomthom098, Mar 13, 2019 at 2:54 PM.

  1. Thomthom098

    Thomthom098 New Member

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    Hello, my 6101LM combo was recently slow to start, taking couple minutes after standby put on 1 and today it does not start at all. It seems to be the preamp as guitare plugged direct in power amp line in works and pream out to an external other power amp does not work. I tried all 3 channels, they seem to switch ok with each led alternating but no sound on any channel. I also tried to tap lamps very gently with a pen after removing metal covers but nothing.

    Any thoughts what to try anyone ? Thank you
     
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  2. Jethro Rocker

    Jethro Rocker Well-Known Member

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    Start with V1 and change each preamp tube one at a time with a different tube. Hopefully one will be the culprit. I'm thinking V1.
     
  3. anitoli

    anitoli Well-Known Member

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    V1 is only for channel 1. V2-V6 is for channel 2. V2-V3-V4-V5 is for channel 3. For all of these channels to not work would require all off these tubes to be bad, not very likely but possible all the same. Now if the amp is putting out sound when using the line in that would indicate that the PI is ok. Have you tried putting a jumper cable into the fx loop and what is the fx loop set on series or parallel?
     
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  4. Jethro Rocker

    Jethro Rocker Well-Known Member

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    Oh right I forgot about V1 being only channel 1. A bad V2 would affect channels 2 and 3 but yeah channel 1 is also suspect. Unless V1 and V2 are goofy.
     
  5. Mitchell Pearrow

    Mitchell Pearrow Well-Known Member

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    Welcome to the forum new brother, the members who have posted before me are very knowledgeable about your amp, and with sound advice! Cheers Mitch
     
  6. 67Mopar

    67Mopar Well-Known Member

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    I've owned many Marshall's over the years. The 61OO was by far the most trouble-prone out of them all. Had Marshall left out the MIDI board, I suspect it would have been a more stable device. The lack of standoffs under the main board was inexcusable.
     
  7. Thomthom098

    Thomthom098 New Member

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    PI ? : Power Amp ?

    Thanks for suggestions. Checked bypassing loop with jumper and parallel / series switch, no sound still

    Would be bad luck to have both V1 and V2 fail simultaneously. If I want to test, should I remove V3 and replace V1 by it, they are all the same (ECC83 ?) or do I need new spares ?

    How about V7, could that failing make all channels silent ? To test I could again take for example V3 and replace V7 with it ?

    Thanks again guys
     
  8. Thomthom098

    Thomthom098 New Member

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    Thank you Mitchell for welcoming me
    What do you mean by "standoffs" Mopar ?
     
  9. Jethro Rocker

    Jethro Rocker Well-Known Member

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    You could do that. V7 is the PI tube and it is part of the power section so doubtful it is the problem as you've shown the power section is workkng. It's also odd that both V2 amd V3 would be failures but worth checkkng.
     
  10. anitoli

    anitoli Well-Known Member

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    Check the voltage at ic202 - ic201 you should see 15+ and 15- on pin 8 and 4. What are you seeing? You can check this with the amp on stand by.
     
  11. Thomthom098

    Thomthom098 New Member

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    Ok, thanks, I need to find ic202 - ic201 on schematics now, are they on preamp schematic ?
    Note: removing preamp tubecovers V1 to V6, I do not remember seeing light in tubes, should they show light and be hot like the large power tubes ? - I'll check again tonight in the dark maybe
     
  12. Thomthom098

    Thomthom098 New Member

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    Got it, in Power Amp: so volt meter between pins 8 and mass should be +15V and between pins 4 and mass -15V ? Amp ON but on Standby ? Thanks
     

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  13. anitoli

    anitoli Well-Known Member

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    Ok if the heaters are not lighting up and the tubes don't get warm that is an issue. Look at the spade connectors on the power supply board right by the fuses, do any look burned or corroded?
     
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  14. Thomthom098

    Thomthom098 New Member

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    It's working again, I did several checks sequentially and am in the end not sure what the problem was... Thanks to all for reactivity and assistance in the mean time !

    - Checked Low / High Power switch, jiggled it a couple times whilst on Standby - no luck
    - Checked Pentode / Triode switch, jiggled it a couple times whilst on Standby - no luck
    - Checked mute power amp input switch was out, checked FX switch series / parallel was out, jiggled them a couple times whilst on standby - no luck
    - I tested guitare plugged directly in FX return - working as goes to power amp direct without passing through pre amp
    - And then plugging guitare back in normal input, the sound came back for a couple seconds... and disappeared again...
    - I then took the amp out of the cabinet and placed it upside down to have good access to valves, removed all V1 to V7 aluminium caps
    - A little "black plastic broken cap looking like" piece fell out so I inspected the inside of the amp carefully and in the ind I indentified it as being an old piece of power tube, the bottom black central cylindrical part - it must have come from an old tube replaced as all 4 power tubes are in perfect condition, they seem to be Russain 6n3C-E 0686 i.e. 6P3S-E in our alphabet, which I think are 5881 (or maybe 6L6GC, not 100% sure here) type equivalent (my amp seems to be the latest latest 6101LM black, Serial is 971751325, have asked Marshall what the original tubes should be...)
    - I switched V1 with V3 and V2 with V4 - sound worked again, all 3 channels, and stayed working this time... :)
    - So I then tested alternatively V2 to V6 in V1 slot and Channel 1 kept working all the time suggesting no pre amp tube is faulty... unless an intermittent fault ?
    - I then switched V3 and V7 and sound still working, on all 3 channels
    - I reassembled it all and the amp works well it seems, cross fingers

    So... not sure what to conclude, I am wondering if a bad contact or an intermittent tube issue in V7 could be the culprit, it was suggested above that V7 the Phase Inverter or Phase Splitter lamp was linked to power amp so not the issue but in the manual, V7, described as Phase Splitter it states "fault all channels dead"

    Question / Advice to you all:
    - Power lamps look good, they are all the same brand / match etc... and seem to be Russain 6P3S-E 0686 - If I want to by 2 spares, what should I get ? JJ 5881 for example or 6L6GC ?
    - Preamp lamps look a bit more messy, I spotted 3 different kinds, one with red markings, one with grey / black markings and 5 without marking at all... - would you recommend I replace them all and buy 2 spares ? What should I get (I am not picky about customization for tone etc..., I just want the amp to work consistently), are standard JJ ECC83s a standard choice for all slots, V1 to V6 as well as for V7 ?
    - I sometimes see ECC83 instead of ECC83s, is there a difference ?

    Thanks Again :)
     
  15. Jethro Rocker

    Jethro Rocker Well-Known Member

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    Excellent news!! Could have been dirty pre tube sockets? I would not replace the preamp tubes as yet, I would give them a good inspection and see what you have there., Could be some real gems in there for type, who knows? Possibly the red ones are National brand Chinese tubes, the 6101 seems to like these tonally. I would get a couple spares of whatever type and maybe pull one of each type, photograph it, and post it here so we can see what's in there.
    As for power tubes it's hit and miss that 2 would match. I guess get 2 JJs and if you ever need to use them, run it on half power mode which just uses the 2 tubes till you can get 2 more.
     
  16. anitoli

    anitoli Well-Known Member

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    Well seems like the problem was a dirty tube pin/socket. Some times pulling them out and reinserting knocks some of the crud off. Glad it's working again.
     
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  17. marshallmellowed

    marshallmellowed Well-Known Member

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    Output tubes should be replaced as a matched set (quad). If you're needing the amp to be reliable for gigging, and have the funds, you might get a new set to have on hand. If your preamp tubes are all working, I'd just leave them "as is". There's nothing wrong with using mixed brands of preamp tubes. You might even want to play around with the positions of the tubes, you may find you prefer the sound of one or more of the tubes in a different position.
     
    Last edited: Mar 16, 2019 at 12:51 AM
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  18. Thomthom098

    Thomthom098 New Member

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    Gems ? Haha doubt it, I paid 350 bucks for the amp - or I got really lucky for once I'll have a look and take photos yes and pay around with V1 position I use most to see if I notice different sounds from different tubes.

    Quick questions:
    - On eurotubes.com I see in the video the guy spraying contacting ? / anti oxydant ? stuff I guess on tube pins, is this good to do ? What type of product is it ?
    - On channel 2, I have quite a big jump in decibels when playing wit A-B and B-C buttons, is it normal ?
    - For power amp, I therefore understand that you suggest to change all 4 or nothing (match set / quad) ? I play on 25W most of the time and always on low power at least - so I wear 2 tubes out only (the 2 central ones I guess, they get boiling hot when playing whereas the side ones stay warm only). Does that mean that I unbalanced the "quad" and I should avoid replaying on high power ?
    - Can the 2 side power tubes be used as spares for the central pair if one breaks down i.e. on low power can the amp be played without the side power tubes in ?
    Thanks all
     
  19. anitoli

    anitoli Well-Known Member

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    The two outside tubes are the ones that are connected to the half power switch, so yes you can pull those out if you are not going to use them, doesn't hurt anything at all. The reason the inner pair gets hotter is they are actually working the outside pair is at idle state.

    I have played around with these amp alot and if you are not setting your bias right at the 70% point but lower if you do pull the outside pair it won't be necessary to rebias, the voltage change isn't enough to make the bias jump that much, it's only around a few watts.
     
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