Radiospares JTM45 indicator - changing bulb?

Discussion in 'The Workbench' started by shakti, Jul 23, 2019.

  1. shakti

    shakti Member

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    I have two of these which annoyingly have died on me recently. One is Radiospares labeled and has the solder tags on the end, the other is the type that looks identical but isn't Radiospares labeled (no label) and has hardwired leads. There is some debate about whether the latter was ever originally used by Marshall, but my clone doesn't care about that...only that it looks right and it wants the indicator bulb to work!

    Is there any way to change the bulb in these? They are becoming hard to find.
     
  2. stickyfinger

    stickyfinger Active Member

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    I haven't changed the bulb yet but they do come apart and I have one dismantled here. Looking to complete the project.

    EDIT- I dismantled a leaded version so don't know.
     
    Last edited: Jul 23, 2019
  3. Chris-in-LA

    Chris-in-LA Well-Known Member

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    Valvestorm sells a 120 volt version with solder tabs and a 6 volt one with hard wires. Do you know which one you need?

    DC81E6D6-8AAE-48A8-9751-8148BE553BF8.jpeg
     
  4. junk notes

    junk notes Active Member

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    Thinking that they were the same, I did not realize that the 6v replacement bulb I happened to get was one of those LED's. My mistake I did not get it from a legit amp site that sells vintage spec amp parts like ValveStorm.
    The LED version was so luminous that you needed sunglasses.
    Did not mind doing the job twice to get it right. All good now. :)
     
  5. shakti

    shakti Member

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    The lamps shown above are the square indicator type that was introduced in late 66. The one I'm using is the type that was used prior to that, and is round. Looks like I can still get a replacement on Ebay, but somehwhat expensive:

    https://www.ebay.co.uk/itm/MARSHALL...rentrq:225659fc16c0ac3c2b023ae7ff5bbfd8|iid:1

    Has anyone succesfully changed the bulb in these, and with what?

    (For the record, I am aware that Marshall used the amber coloured ones, but those are very rare and stupid expensive, so red will have to do).
     
  6. Chris-in-LA

    Chris-in-LA Well-Known Member

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    I thought you said that your clone didn’t care.
     
  7. fifteenohms

    fifteenohms Well-Known Member

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    Jerry Blaha once told me the 6V originals affected the tube operation and gave a sag to the sound, which if changed to 120v somehow ruins the tone.

    If you had a 6v only use that to replace per that reference.
     
  8. shakti

    shakti Member

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    I can't see how a bulb wired to the heaters would affect sag in any way. But feel free to educate me.

    My clone doesn't care if the lamp is Radiospares or similar non-RS, and whether it's red or amber. But it cares that it looks correct for a mid-60s clone and that it works.

    So the question remains; is there anywhere to get a replacement bulb (240V or 6,3V) and is it possible to put that into the existing lamp?
     
  9. neikeel

    neikeel Well-Known Member

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    I have never had one fail (unlike the red square ones!). If you are stuck I have both amber and red, solder lug and red wire versions knocking around.
    I looked at the design and can only see that it will come apart by cutting the white body off because undoing the crimp will almost certainly destroy the chrome part.
     
  10. shakti

    shakti Member

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    I'll PM you Neil. :)
     
  11. Guitar-Rocker

    Guitar-Rocker Well-Known Member

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    I find it rich that there is an idea that filament indicator lights affects tone

    Changes in B+ / charging and discharge pulses of reservoir caps affect sag.
     
    Last edited: Jul 24, 2019
  12. Gene Ballzz

    Gene Ballzz Well-Known Member

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    Yes, but, well, ya know, but, but, maybe, seeing as how the color or the wire insulation can affect tone, well, ya know...... :run: :rofl: :rolleyes:

    Who Loves Ya baby! :cheers:
    Gene
     
  13. ampmadscientist

    ampmadscientist Well-Known Member

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    Normally there is no way to change the original bulb.
    But with certain modifications, there might be a way to change the bulb.
    In the meantime, there is replacements which approximate the original appearance.
     

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