Blowing Pilot Light on Bench Test of New Build

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danward
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Blowing Pilot Light on Bench Test of New Build

Post by danward »

Good Evening All!! Just finished wiring 18 Watt TMB. I keep blowing the Pilot Light - Testing Amp - No Tubes in -
18 Watt Layout .png
Turn on Main Swith - pilot light blows - Fuse has not blown - what are the potentential issues?? - Wiring Diagam in the attachements - Thanks to all in advance - Dan
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JMPGuitars
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Re: Blowing Pilot Light on Bench Test of New Build

Post by JMPGuitars »

My first thought would be that if you're running the pilot on the mains as drawn, the bulb would need to be rated for at least the mains voltage you're applying to it.
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danward
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Re: Blowing Pilot Light on Bench Test of New Build

Post by danward »

That crossed my mind as well - I used a fender bayonet style light - looking into the voltage of the fender bulb vs Marshall spec now - double checked all wiring and don’t see any grounds or deviations
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Re: Blowing Pilot Light on Bench Test of New Build

Post by TriodeLuvr »

Doesn't Fender use low voltage bulbs like the #47? That's a 6V bulb.

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Re: Blowing Pilot Light on Bench Test of New Build

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Look at the metal sleeve of the bulb. It should show the voltage rating...
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Re: Blowing Pilot Light on Bench Test of New Build

Post by JMPGuitars »

TriodeLuvr wrote:
Tue 01/26/21 1:14 am
Doesn't Fender use low voltage bulbs like the #47? That's a 6V bulb.

Jack
Yes they do, as do I. But I have it connected to the heaters, not the AC mains. If you check F*nder's schematics, you'll see they do the same. Voltage ratings don't usually lie that much.

To connect to AC mains, the bulb has to be rated for that voltage. If you want to connect a 6V pilot, use the heaters instead of the mains.
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Re: Blowing Pilot Light on Bench Test of New Build

Post by Bieworm »

I have my amps pilot lights on the 230V primary. I did this because maybe there would be a possibility to generate extra noise on the heater wiring when the pilot light shares those wires... but i now trust that's not the case
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Re: Blowing Pilot Light on Bench Test of New Build

Post by JMPGuitars »

Bieworm wrote:
Tue 01/26/21 10:25 am
I have my amps pilot lights on the 230V primary. I did this because maybe there would be a possibility to generate extra noise on the heater wiring when the pilot light shares those wires... but i now trust that's not the case
The most important thing is the quality of your work (and obviously that the lamp be rated for where it's being connected). The other thing is that when I build an amp with a solid state rectifier, I use the unused rectifier heaters for the pilot lamp instead of the regular heater connections.
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Re: Blowing Pilot Light on Bench Test of New Build

Post by TriodeLuvr »

JMPGuitars wrote:
Tue 01/26/21 6:48 am
TriodeLuvr wrote:
Tue 01/26/21 1:14 am
Doesn't Fender use low voltage bulbs like the #47? That's a 6V bulb.

Jack
Yes they do, as do I. But I have it connected to the heaters, not the AC mains.
Right, but my point was that the OP probably has a 6V bulb in the Fender holder connected to the mains. That's why it's blowing. He needs to rewire it, assuming the filament winding can handle the additional 150mA for a #47 or #1847 bulb. He could possibly use a neon bulb (assuming the holder is rated for 115/230V), but it probably won't be bright enough, depending on the color of the jewel.

Jack

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Re: Blowing Pilot Light on Bench Test of New Build

Post by danward »

TriodeLuvr wrote:
Tue 01/26/21 1:14 am
Doesn't Fender use low voltage bulbs like the #47? That's a 6V bulb.

Jack
Thanks Jack, Yup 6 v bulb! it put up a good fight - a quick 2 bright seconds and - darkness!! - 120 volt replacement on order -
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Re: Blowing Pilot Light on Bench Test of New Build

Post by JMPGuitars »

TriodeLuvr wrote:
Tue 01/26/21 12:31 pm
Right, but my point was that the OP probably has a 6V bulb in the Fender holder connected to the mains. That's why it's blowing. He needs to rewire it, assuming the filament winding can handle the additional 150mA for a #47 or #1847 bulb. He could possibly use a neon bulb (assuming the holder is rated for 115/230V), but it probably won't be bright enough, depending on the color of the jewel.
We agree. ;)
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Re: Blowing Pilot Light on Bench Test of New Build

Post by crgfrench »

Connecting a 6V bulb to the heater line will not add noise. If you have good lead dress.
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