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PREVENT UNDUE HEAT

Discussion in 'The Workbench' started by VERVEHAMMER, Sep 20, 2021.

  1. VERVEHAMMER

    VERVEHAMMER Member

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    I'm sure this has been done before, but I wanted to contribute something useful to the Marshall Maniacs here. (raises 40oz King Cobra Malt Liquor)

    My first Fan Cooled Amp was (and still is) a MKIII Boogie and the tubes lasted a very long time.

    After seeing many warped vents on top of 100 watt Marshall heads, I decided to prevent Excessive Heat by adding a fan. I've seen permanently mounted fans before and it's just not my style.

    No, I didn't mod anything and this simple set up can be easily unstrapped. I've used it for years, on all heads. It simply hangs off of the back by the handle and plugs into the power strip.

    If any have any improvements on my "Cave Man Thag Cools Amp",
    Please share...

    Up the Irons!
     

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    Last edited: Sep 22, 2021
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  2. ricksdisconnected

    ricksdisconnected Well-Known Member

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    i guess thats one way to do it.
     
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  3. Dogs of Doom

    Dogs of Doom >>> Moderator <<< Staff Member

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    you could screw it on, to the rear grill...
     
  4. PelliX

    PelliX Well-Known Member

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    I do the same, though I made a permanent fixture bolted to the back panel. Also, flip the fan the other way around, that avoids directly blowing air on the valves and give you a little protection against stray cables or fingers.
     
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  5. VERVEHAMMER

    VERVEHAMMER Member

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    Depending on the operating environment temp, I sometimes slide the fan down to the pre-amp end to not blow directly on Power Tubes, (though it works fine in my warm climate)
    I'll get rid of the velcro and use a dog collar or clip-lock strap soon, it keeps things flexible and transferable amongst amps, and they will still fit in the flight case just fine. ATM I'm absolutely raging the EVO Hot Mod, and experiencing a Marshall Revival of Inspiration. If music is my Aeroplane, I'm Flying High Again.

    I truly appreciate this Forum and all comments!
     
    Last edited: Sep 22, 2021
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  6. william vogel

    william vogel Well-Known Member Gold Supporting Member

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    I run my amps with the rear panel off. I have no small children or un knowing people around my equipment that could risk burns. Your situation could be different. Without the panels in place, airflow is good.
     
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  7. PelliX

    PelliX Well-Known Member

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    Heads are generally fine, indeed. Combos will melt themselves into oblivion, that's what "inspired" me to get something like a fan in place.
     
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  8. Pete Farrington

    Pete Farrington Well-Known Member

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    The big problem there is that most users and many techs think that hot valves are the only hazard that then becomes exposed.
    The rear panel is a key safety feature of many amps, an essential barrier between the user and the significant electrocution hazard of series connected HT can caps.
    See https://www.thegearpage.net/board/i...radial-caps-and-electrocution-danger.2022648/
     
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  9. anitoli

    anitoli Well-Known Member Gold Supporting Member

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    Vacuum tubes can't operate unless they are hot.....???????
     
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  10. PelliX

    PelliX Well-Known Member

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    Correct, but technically it's the temperature on the inside, not the outside. There is nothing wrong with cooling the valve on the outside within reason. The main concern here is not that the valves themselves get hot, but other components get heated (capacitors, resistors, etc).
     
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  11. alpha al

    alpha al Member

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    I've done this on a few Peavey Classic 30's. Had a fab shop make the metal bracket. Screwed it to the inside of the amp with a couple screws. It's a 240V fan, and runs slow on 120V so it's not noisey. I tapped it onto the amp's AC power circuit, after the on/off switch.
     

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  12. MP+

    MP+ Member

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    Similar solution to alpha al. My Silver Jubilee 50 watt ran so hot that after high volume rehearsals the valves practically fell out of their sockets. Part of this is a design fault as far as I'm concerned with the move of cramming a full blown 50 watt chassis into the miniature "club sized" cabinet with no vent. Everything only just fits in that sleeve, the power transformer has a gap of about 1" from the top board and this is the component that really heats up. It looks to be a common problem from what I've seen. I did see a Jubilee head like mine selling on ebay some time ago which was advertised as being part of the gear of "Primus". Someone hacked the side out of the cabinet next to the power transformer and mounted a fan right there. I could understand the move but it wasn't for me. I went down the path of alpha al and mounted a fan inside but with a twist. My boy was hot rodding his custom gaming computer with a liquid cooled CPU. The old CPU cooling fan just looked perfectly dimensioned and it had this great looking aluminum heatsink attached to it. I screwed it directly to the timber where it just fits internally between the power transformer and the case with the heatsink facing into the timber, that way any crap that gets blown in just gets thrown at the timber wall. It is the perfect solution, you can barely hear it over the amp hiss and the power transformer runs cool for hours. Invisible and reversible without a trace. The sound of the amp has improved since there was previously no way to stop the valves from running too hot. The only complication was the fan being 12 volt DC. I overcame this by securing a wall wart style power pack under the chassis and run two wires out through one of the transformer wiring grommets. This is then joined to the wiring of the fan via a small PCB style connector which can be unplugged if you want to remove the chassis for any reason or switch the fan off.
     
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  13. VERVEHAMMER

    VERVEHAMMER Member

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    A+ Alpha Al!
    Your fan set up (in the floor of the combo's cabinet/housing pointing up towards the Power Tubes), is nearly identical to the factory installed Mesa/Boogie MKIII Simul-Class 75 1x12" Combo. It lays flat, approximately 5" below the quad mix of 6L6/EL34's. Good Job!

    Yes, I dusted after snapping the pic. : )

    Preventing Undue Heat extends ALL component's service life.

    Crank it up!
     

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  14. VERVEHAMMER

    VERVEHAMMER Member

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    Cave Man Thag Budget Amp Fan recipe...
    Radio Shack Cooling fan 4.75"x 2.0"
    +
    salvaged power cord from an cheapo digital alarm clock.

    Keeping the fan separate from the amp circuit has a few advantages...
    In my manual, Boogie describes how one can disconnect the fan to record, if needed. It came factory hard wired/no switch.

    I like how I can continue to let the fan cool the tubes a few minutes after powering off the amp. As you all know, tube's are most subject to shock damage when hot and this can help prevent that when relocating the amp after the throw-down ritual.

    Obviously, a well positioned Box Fan can also be effective, non-invasive, and cheap. Whatever it takes...
     
    Last edited: Sep 22, 2021
  15. junk notes

    junk notes Well-Known Member

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    Interesting; probably why some of the experts do not consider tube sinks to be a solution for dissipating heat off a vacuum tube; technically off the glass.
     
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  16. PelliX

    PelliX Well-Known Member

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    Yes, but you're also cooling them down faster than one would generally (normally the heaters go off with the amp and rest of the heat is dissipated into the room). This is specifically one of the reasons I don't blow on the valves but rather pull warm air out. @alpha al seems to be doing the same, unless the fan is running backwards. After all, there's no problem in the valves themselves heating up - they're designed to do that. The PCB's, capacitors, etc are what one is generally trying to protect.
     
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  17. PelliX

    PelliX Well-Known Member

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    I think that would just be technically rather cumbersome to do. Heatsinks could do a lot, but where is that heat going then? Copper pipes running off the valves would transfer some, but not all of the heat, so it's not really solving the problem. Also, valves need to be hot to work correctly, starving the heaters would do the trick - but that's not a good idea either. The solution, in my opinion, is to cool the chassis and keep the valves hot. :shrug:
     
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  18. jmp45

    jmp45 Well-Known Member

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    Previous owner of my 72 Major hacked the side of the cab and not a good job at that. Mounted a fan and connected to mains. I opted to install a normally open thermal switch in the top of the cab that will close around 140f IIRC, or around there. It kicks on at around 25 minutes.
     
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  19. VERVEHAMMER

    VERVEHAMMER Member

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    Undue, or Excessive, is the operative word here, and that's for the User to decide.

    The Mesa Boogie Factory Installed Fan blows directly on the Quad of Power Tubes. It does not pull air away.
    These amps are made to withstand touring which includes direct sunlight on Summer stages. (Which has cooked many a Marshall) Randall Smith and Mike Bendinelli got it right. The Cooling Fan, Graphic EQ, and Reverb were options.
    I live in a warm/hot climate, and fan cooling works for me perfectly, has for years. If you don't ever have to move a hot amp, no worries. Those bumps that hot tube takes may not take it out immediately, but can contribute to an early demise.

    Your Mileage May Vary. I appreciate all comments. : )
     
    Last edited: Sep 22, 2021
  20. VERVEHAMMER

    VERVEHAMMER Member

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    That's pretty custom Jtm45.

    You just inspired me!! Damn you're smooth!! : )

    I want it switchable, off, low, high. Therefore my new mission will be installing a variable resistor/switch in the power cord between the fan and plug. (like a heating pad control).

    This keeps the detachability/portability of my simple rig.

    Thank you, SIR!
     
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