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Thread: Laney LC15R - too much heat - should I install a fan ?

  1. #36
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    Hang on...

    A well designed iron-cored power transformer should be 97% efficient or better. A really badly designed and cheaply built one might be less than 90% efficient.
    I find it hard to believe that even Laney, some of whose products are, shall we say "aggressively cost-engineered", would tolerate 80%.

    The fact that a transformer is "too hot to touch" doesn't tell us very much. Its not uncommon to run transformers at over 100C. Lamination and winding temperatures may be different, depending on construction and how much the chassis heatsinks the core.

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  2. #37
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    Quote Originally Posted by Ted View Post
    Hang on...

    A well designed iron-cored power transformer should be 97% efficient or better. A really badly designed and cheaply built one might be less than 90% efficient.
    I find it hard to believe that even Laney, some of whose products are, shall we say "aggressively cost-engineered", would tolerate 80%.

    The fact that a transformer is "too hot to touch" doesn't tell us very much. Its not uncommon to run transformers at over 100C. Lamination and winding temperatures may be different, depending on construction and how much the chassis heatsinks the core.
    Hi Ted..
    I got an email from a Laney tech, and he says the PT has been used for 15 years and is supposed to run hot 60-70 degrees.. and it is spec. to 12 degrees.
    The tech guy suspected the two small yellow thermo-switches (F2 and F3) in the low voltage supply line (feeds bias, reverb and effect loop) to be bad. There has been much writting on the large yellow thermo switch (F1) in the filament supply line to be bad (bad batch from the supplier). And people have either changed it or bypassed it.
    I have bypassed all three thermo-switches and left the amp on when biased at 19mA and 22 mA with two jj EL84 tubes and it takes a bit longer for the power transformer to heat up, and though hot to the touch it was slightly "cooler" than before..
    I left the amp on for three hours and the idle dissipation was rock solid within 0.5mA of drift. So removing the yellow "bastards" seem to have worked..
    Last thing to note is that a standard EL84 should according to the vintage mullard datasheet pull 760mA of filament current but BillM meassured a 830mA draw on the jj EL84 so they might eat a bit more current than the supplied rubys, that also behaved very different in terms of idle dissipation at a given bias voltage. (20mA at idle, JJ EL84 ~ -8.6V, 20 mA at idle stock tubes ~ 12V).

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  3. #38
    Senior Member chazpope's Avatar
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    hey barfoden, beats me where these 'switches' are? Do you mean you bypassed the FUSE F1 ? Not very clever is it

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    Quote Originally Posted by chazpope View Post
    hey barfoden, beats me where these 'switches' are? Do you mean you bypassed the FUSE F1 ? Not very clever is it
    Nahh.. you are right ,, not really clever having no fuse in the filament line.. I will have to shop around and find a suitable 7A regular fuse to put in that position. That is what the fender excelsior have in the filament line.. Some amps have no fuse in the filament line. In the schematic for a pp18 (18 watt lite iib clone) from ampmaker I see no other fuse than the main supply fuse.

    The small round yellow ones in F2 and F3 I really can't be bothered with .(low voltage supply for the reverb and effects loop)..

    All i know is that the amp seems stable now, and the pilot light is dead stable within at least 3 hour when powered up..

    I did pull a preamp v1 tube too see if the filament line was drawing excessive current. The idle dissipation on the EL84 i was measuring on when from 21.2mA to 21.7mA. So it does not seem to be loaded down too much. I think the JJ EL84 I have in there draw slighly more (830mA each) than the stock tubes (750-760mA). They (JJ EL84) also need much less bias voltage to have the same idle dissipation compared to the stock ruby tubes.

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  5. #40
    Senior Member chazpope's Avatar
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    .. this thread is about LC15R. Are you talking about that or some other amp ?

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  6. #41
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    Quote Originally Posted by chazpope View Post
    .. this thread is about LC15R. Are you talking about that or some other amp ?

    I have a Laney cub 12r.. THe amp is very similar and it uses the same power transformer, which A Laney tech told me about.
    He told me that the PT in these amps, with the Laney VC15 included runs hot at 60-70 degrees celsius.

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  7. #42
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    And here's mine - Not being so confident tapping into the circuit my buddy advised me to simply power it from an external 12v power supply. So, piece of plywood cut, fan and DC socket fitted - job done. Work's a treat! Thanks to everyone here for all the really useful info.
    Click image for larger version. 

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  8. #43
    Old Timer J M Fahey's Avatar
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    FWIW I donīt double voltage and then regulate it down but simply half wave rectify (no worry about a little ripple here) with an 1N4007 +2200uFx16V to get some 8V DC and feed the 12V PC fan with it.
    It works very well.

    Fan runs at somewhat slower speed, moves somewhat less air, makes NO noise, yet airflow inside the enclosure is still tons better than unaided, and enough to keep things cool.

    I donīt actually need maximum possible airflow into a tiny heatsink but simply to get fresh air in and warm out all the time.
    In the grand scheme of things the transformer does not even notice the tiny extra consumption.

    Of course that 8VDC supply is floating, no part of it is connected to ground.
    The fan does not care anyway.

    I just mention this because once I explained this add on to a customer over the phone ... and he connected the 2200uF cap negative to ground "because thatīs where electrolytic negatives go" ...
    So better safe than sorry.

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    Juan Manuel Fahey

  9. #44
    Old Timer olddawg's Avatar
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    What I don't understand is if you are worried about excessive heater current causing the PT to run hot, why would you ever add a fan to the filament supply? Use a 120v ac fan or power a low voltage fan with a wall wort!

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  10. #45
    Bent Member Chuck H's Avatar
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    I've used 120V fans with no problems, noise or otherwise. This, provided you and your amp are in a place that has 120V mains I suppose, simplifies installation as well. Remember that you want the fan sucking hot air away from the tubes and not blowing cold air directly on them.

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    "In fact when I run into problems working on electronic circuirts, there are so many times that when I finally track it down, the source of the problem is located between my soldering iron and my seat." SoulFetish

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