How Much Is Too Much...

Discussion in 'Marshall Amps' started by SHREDNECK, Jul 21, 2018.

  1. SHREDNECK

    SHREDNECK New Member

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    ...Chassis Heat?

    My full rig consists of two vintage Marshall tube heads, each over two individual 8x12 full stacks.
    Both were bought new back in the day, and I've been employing them in my current rig configured as Master / Slave since 1992. More on the rig configuration later...

    The heads are:
    * JCM 800: 2204 50 watt, single- channel (bought in Philly, 1984);
    * 30th Anniversary: 6100, 100 watt, triple- channel (bought as 8x12 full A/B stack from a metro Denver retailer in 1992).

    Not too long ago, I brought both heads to an outfit here locally to have them each re- tubed and biased. Wound up having to lay out $800+ in three trips total, with regard to addressing work needed, both in terms of initial repairs done, and consequential follow- up repairs in dealings with said outfit.

    This primarily centered around the anniversary head. Some problems were identified and addressed initially, however the 6100 wound up with more problems cropping up during and following the initial trip to this vendor.

    The 30th anniversary head now has been re-tubed and biased twice by these gentlemen, but now -- with 'original ills' taken care of; it seems that the chassis physically produces a great deal more heat than I recall having previously encountered prior to taking the two heads into their shop.

    Regardless whether on standby or during normal use, both situations present the same overheating conditions even after a mere 40 minutes or so. It gets to the point where the front left chassis panel becomes a good deal too hot to the touch.

    The 2204 does not produce excessive heat in the range the 6100 is experiencing. I want to note as well the 50 watt / 2204 chassis cabinet does not have a vent grill on the top, whereas the 100 watt 6100 does. The high heat has not produced any malfunctions to date; I'm lucky in that regard, I believe.

    Has anyone else seen this condition? The 6100 head sports seven (7) 12AX7 pre tubes with four (4) EL34 power tubes and a mutha of a power transformer. It'd indicate to me that this 6100 head should run somewhat hotter than the 2204, being 100 watt with a sh*tload of valves, as compared to the 2204's three (3) 12AX7s with two (2) EL34 power tubes @ 50 watts.

    Some of what the technicians there have told me regarding configurations and use are outright whoppers. If she needs to go to the shop again, well... it's not going back to these folks, withstanding completion on their part of all warranty work which has popped up while in their possession (and I'm not completely firm in that regard).

    I'll leave things here at this point for now; any input from the members is welcome and encouraged.

    THANKS!!
     
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  2. JeffMcLeod

    JeffMcLeod Well-Known Member

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    "SHREDNECK"

    lmao! :lol:
     
  3. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    If the amp is biased wrong, this will cause excessive heat.
    It kind of sounds like you need to find real technician.

    If you take the back off, and look at the power tubes when the amp has been running, you may see the power tubes turning red...which is a bias failure.

    Where are you located?
    Might be able to help you find somebody qualified. At least take it to have the bias checked out.

    This is a pretty easy test...
     
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  4. SHREDNECK

    SHREDNECK New Member

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    He He He.... kinda taken with it humorously and literally (wish it weren't in all caps though, Ha!)
    Came up with the name back when I registered, hoping it was original. :fingersx:

    Not so much nowadays, I'm sure.

    - 'SHREDNECK' Bruce :jam:
     
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  5. SHREDNECK

    SHREDNECK New Member

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    @ampmadscientist:
    I'm with you all the way, thanks! I'm located in Denver, and will be looking into the biasing issues if any.

    *edited with added text:

    Hey, thanks for your input and guidance regarding the 6100 overheating issue; I appreciate it! And, with regard to that impressively long list of technical repair shops in Illinois, I as well appreciate the endeavor, but I needed to be more clear on my location, which is Denver, Colorado. I have lingering issues still unaddressed with regard to this particular shop, under the name 'Vacuum Tube Supplies' at 700 Mariposa Street, as well in Denver.

    Over the 35 + years playing, writing, recording and doing studio sessions, I've had some GREAT shop owners / technical engineers, but over the years two have since passed -- and these guys really knew their sh*t. Replacing technical engineers with equally qualified and experienced techs currently has me at a local disadvantage.

    -- BG
     
    Last edited: Jul 22, 2018
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  6. BowerR64

    BowerR64 Well-Known Member

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    Hook it up like you normally do and play threw it for a bit with the back grill off so you can see the tubes glowing.

    The tubes on the left are normal, the tube on the right is what red platting looks like and if any of the tubes in your amp look like this shut it down and dont use it again till its serviced.

    Red plating.jpg

    I would think red plating would draw excessive current and pop fuses
     
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  7. Adrian R

    Adrian R Well-Known Member

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    The amp is running 'under biased' or too hot...allowing too much current to pass through the tubes. 50w Marshalls never had vent plates.
     
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  8. Adrian R

    Adrian R Well-Known Member

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    I've actually painted the back panel/grills flat black so I can easily see how the tubes are running without removing the cover. Works great. The non painted silver surface reflects ambient light back in your eyes making it difficult to see the level of tube illumination. The black surface allows for good contrast...
     
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  9. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    Then you just need to check the bias, because that's what can make it run too hot.
     
    Last edited: Jul 21, 2018
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  10. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    Oopps sorry, wrong state...
    • Sound Electronic Service
      6429 Miller St #B
      Arvada, CO 80004-2800
      Ph: (303) 467-0664
    • Musicians Custom Electronics
      2369 S Trenton Way, Suite N
      Denver, CO 80231
      Ph: (303) 668-2122
    • Vacuum Tube Supplies LLC
      700 Mariposa Street
      Denver, CO 80204
      Ph: (303) 534-5170
    • Glenwood Music
      3102 Blake Ave Ste D
      Glenwood Springs, CO 81601
      Ph: (970) 928-8628
    • Downtown Sound
      330 E 4th St
      Loveland, CO 80537
      Ph: (970) 673-0006
    • Fireweed Music c/o Elledge Music
      518 W Northern Ave
      Pueblo, CO 81004
      Ph: (719) 545-2617
    • Rapid Electronics
      518 W Northern Ave
      Pueblo, CO 81004
      Ph: (719) 544-4478
     
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  11. SHREDNECK

    SHREDNECK New Member

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    AWESOME! Good on ya; I now have a lot of tools at my disposal to eventually find the right fit, technician - wise.

    Thanks yet again! :cool:
     
  12. anitoli

    anitoli Well-Known Member

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    6100's get warm but not so hot you can't touch the chassis. The hottest part aside from obviously the tubes will be the power transformer after some time but still not so hot you can't hold your hand on it. I have run mine into a Rockcruser with the MV between 12 and 3 o'clock and even then you can still put your hand on it. I am going to have jam out tonight i will take a temp reading for you of the PT as i will be cranking this amp for hours just to give you a reference point as to how hot mine are running.
     
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  13. ampmadscientist

    ampmadscientist Well-Known Member

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    Start the reactor... Free Mars!
    From the wave form Anitoli posted, his amp is biased pretty hot...hotter than usual.
    I can tell that by the wave form on the scope.

    (he biased according to bias formula)

    The amp could be biased cooler, without excessive distortion (if the amp is biased with a scope.)

    But of course, hotter bias does sound better, for sure. But the tube life is shorter.
    So, it's really just a compromise between longer life (colder) and better sound quality (hotter).

    anatoliwave.png Actual Anitoli wave form, just before clipping.
     
    Last edited: Jul 21, 2018
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  14. SHREDNECK

    SHREDNECK New Member

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    What great testimonials and advice on this thread thus far - It's very much appreciated; all of it. As far as the stacks go, they're actually oriented in such a way that I can see the EL34 power tubes following bottom to top illumination within both heads. I've observed the same 'normal' condition on each of the heads -- as I understand tube layout and function following powering up, I'll make this example: After powering up with both stacks on standby, first the base heating filaments / cathodes are illuminated with a neon orange color. There has been no broad red glow observed along the grids, bottom to top ending at the plates / anodes which are all similarly glowing a warm neon orange. I also noted that familiar blue hue dancing at the tops of all four EL34s in the 6100 while being played at a hot level.

    Before I take it anywhere, I'll be pulling the rear grill face and look for any more tell-tale signs more objectively.

    I put them on line and slowly increased the master stack volume to a point where the driven dBspl was pushing pretty hard, and the EL34s in both heads continue to appear as though everything was freshly placed on line.

    With regard to heat, it is still an issue, but concentrated only at a particular area on the left front panel directly adjacent to the power / standby rocker switches and the rig's master volume, inclusionally beside the largest of the three transformers.

    So far, the rig runs great with no obvious glitches, and it sounds killer as always.

    +++++++++++++++++++++++++++++++++

    Am I back to square one with the heat buildup? Not at all. Knowledge, understanding with experience shared and sound advice (sic) are at a level now a good deal beyond where I started. I must also note the red status LEDs on the rear of the head which used to illuminate as the initial malady, indicating internal output fuse failures on the 6100's EL34 power staging in pairs. This has been remedied.

    I'm going to search the resources provided so kindly by ampmadscientist, and I value every bit of advice from the MF Community (had to chuckle typing that).

    *Edit to include:
    Thank you all, any further input is still encouraged, as previously stated -- the quest is apparently in full swing to locate the right tech around here somewhere, and print out the thread pages with copies of all invoices to take along.

    - SHREDNECK Bruce
     
    Last edited: Jul 22, 2018
  15. SHREDNECK

    SHREDNECK New Member

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    Wow, I respect your kind offer here, I would welcome such an overture indeed. Thanks a lot -- :dude:
     
  16. SHREDNECK

    SHREDNECK New Member

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    COOL!! Appreciate ya, man!! :fingersx:

    - Bruce
     
  17. neikeel

    neikeel Well-Known Member

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    I thought 6100s ran 5881s. Shows what I know!
    Or are there different versions?
     
  18. anitoli

    anitoli Well-Known Member

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    The first versions LE and Anniversary badged amps ran EL34's. Then when moving to the LM's they switched to 5881/6L6GC.
     
  19. anitoli

    anitoli Well-Known Member

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    Ok this is what i measured for temps on my 6100 after 4 hours of playing into an attenuator with the MV on 12 O'clock:

    Top of power transformer: 107
    Top of chassis by PI: 111
    Top of switches on front plate: 98

    Bruce if you could get a temp reading from your amp the comparison would be invaluable.
     
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  20. purpleplexi

    purpleplexi Well-Known Member

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    You've been using a 150 watt 8x12 since the 90s?

    I SAID YOU'VE BEEN USING A - oh never mind.......
     

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