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Thread: 110V Pilot Lamp in 220V Marshall Clone

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    110V Pilot Lamp in 220V Marshall Clone

    Greets.

    I am building up a 100 watt clone - either superlead or 2203 - I haven't decided quite yet... thinking of a switchable version to have both - anyway...

    I sourced the chassis from Tube Amp Doctor... and for the indicator light, they had only one version (that I saw) that will work with their chassis/control plates without modification.

    However, the pilot light is for 110V / US. TAD page here, TAD Pilot Lamp, states I could use a 56k 5Watt to use 220VAC with.

    I seem to have little choice here without chewing up the control plates to put in a larger one... So would I simply need to add that 56K resistor in series with one side of the pilot light? I assume it matters not which side, but I must admit I am unsure if the pilot light is to go in series with the live, or if it needs to see live and neutral. I typically have always used 6.2V and ran the heaters through it. Marshall schematics suggest that it needs to see live and neutral. Better safe the sorry

    Sorry for my ignorance here.

    Here is the schematic I am using... Marshall 1959 - at least for the power section. So live goes to the fuse/power switch before it reaches the primary, where neutral goes right to the primary. So if I need to attach this pilot to live and neutral, I'll have to rewire a bit.

    Thanks

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    Lifetime Member Enzo's Avatar
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    You would never run the mains current for the whole amp THROUGH a light. Think about it, that describes the circuit of the "light bulb limiter" gadget we use.

    The light goes ACROSS the mains supply. SO yes, hot and neutral. SInce the light was meant for lower voltage, the resistor drops voltage from the 220v mains to a useful level. SO the resistor is in series with the light, and the whole light plus resistor across mains hot and neutral.

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    Quote Originally Posted by Enzo View Post
    You would never run the mains current for the whole amp THROUGH a light. Think about it, that describes the circuit of the "light bulb limiter" gadget we use.

    The light goes ACROSS the mains supply. SO yes, hot and neutral. SInce the light was meant for lower voltage, the resistor drops voltage from the 220v mains to a useful level. SO the resistor is in series with the light, and the whole light plus resistor across mains hot and neutral.
    Thanks.

    It makes total sense... just needed to make sure!

    Does it matter which side? Live or neutral?

    Thank you!

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    Supporting Member loudthud's Avatar
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    If the power transformer simply has taps for 240V, 220V, 120V, 100V you simply hook the pilot lamp between 0V and the 120V taps. Then it gets 120V no matter what tap the Mains is connected to. If the PT has the series-parallel type primary, the pilot lamp connects across one of the windings before it gets to the selector switch.

    Example: https://el34world.com/charts/Schemat..._50w_2204s.pdf

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    Quote Originally Posted by loudthud View Post
    If the power transformer simply has taps for 240V, 220V, 120V, 100V you simply hook the pilot lamp between 0V and the 120V taps. Then it gets 120V no matter what tap the Mains is connected to. If the PT has the series-parallel type primary, the pilot lamp connects across one of the windings before it gets to the selector switch.

    Example: https://el34world.com/charts/Schemat..._50w_2204s.pdf
    Crazy - I would have never thought of it. Thanks!!

    Wonder why TAD wouldn't just say that? They seem to make it difficult to use anything other than their items for the chassis... I had to buy a new power tranny from them because my hammond PT woun't fit without some serious chopping... the hammod OT, which is "supposed to be" a direct plexi replacement didn't fit without drilling.

    annnnyway... thanks!!

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    Lifetime Member Enzo's Avatar
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    They DID just say that. they offered the 220v alternative in case

    to be internaly connected on 110V tap of all PLEXI Amp Kits or vintage Marshall Amps

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    Supporting Member loudthud's Avatar
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    Most people don't realize you can use the primary of a transformer as an auto-transformer (within reason !). You can even use a small filament transformer the same way as the pilot light is connected if it doesn't have the same kind of primary as your main power transformer.

    Many of the early Marshall schematics don't show a pilot light unless it's the 6.3V kind. They eventually figured it out so the neon pilot light looks the same no matter what the Mains selector is set to.

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    Quote Originally Posted by Enzo View Post
    They DID just say that. they offered the 220v alternative in case
    haha - I read that as used for 110V powered trannys only (as in USA only) - my mistake.

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