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Tube Amp Building - Tweaks - Repairs / Re: 5E3 Build Smoke Comes out of Resistor

« Last post by tubeswell on January 23, 2026, 10:49:23 pm »

Something at that node is drawing enough current to kill that resistor.  I'd be inclined to think it's the filter cap for that node, but it could be anything there.

^This^


The reason the resistor is smoking is its drawing too much current.


The two pathways that draw current from that resistor are the 6V6 greens and the preamp B+ supply.


Therefore, assuming the amp was built properly, there could be either a failure (short) across the screen node filter cap, or a short on one of the 6V6 screen grids that is dumping excess current to ground (causing all B+ voltage to be dropped across that resistor). Or it could be that you have a short to ground behind the board at that filter cap's power supply node.  If the screen filter cap voltage node measures '0VDC', then it's most likely one of this possibilities.

Please measure the PS rail voltages on all filter cap nodes and report back

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Tube Amp Building - Tweaks - Repairs / Re: 5E3 Build Smoke Comes out of Resistor

« Last post by AlNewman on January 23, 2026, 09:04:07 pm »

Sounds like a good time to build a light bulb limiter.

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Tube Amp Building - Tweaks - Repairs / Re: 5E3 Build Smoke Comes out of Resistor

« Last post by apeontheweb on January 23, 2026, 08:45:25 pm »

Yeah the resistor is a bit bulkier than the others.

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Tube Amp Building - Tweaks - Repairs / Re: 5E3 Build Smoke Comes out of Resistor

« Last post by JPK on January 23, 2026, 08:33:51 pm »

Was it 2 watt? It should look like it. Much bigger. If not look at the tube socket wiring. Make sure it's all correct.

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Tube Amp Building - Tweaks - Repairs / Re: 5E3 Build Smoke Comes out of Resistor

« Last post by apeontheweb on January 23, 2026, 08:30:22 pm »

Yes it is a 4.7K not a 47K. I also verified with my multi meter. I apologize for my lousy communication when I accidentally said a 47K resistor.

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Tube Amp Building - Tweaks - Repairs / Re: 5E3 build troubleshooting

« Last post by JPK on January 23, 2026, 08:18:05 pm »

Seems like the electrolytic caps are correct polarity. No idea why it would blow. You'd think the PT primary fuse would have blown. Just happened on my recent build of a different amp. I left a rectifier diode lead long while populating the board and forgot to clip it off before I mounted the board. Diode lead shorted the HT directly to the metal standoff/ground and blew the primary fuse. So thankful my PT didn't fry. That was a silly mistake.

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Tube Amp Building - Tweaks - Repairs / Re: 5E3 Build Smoke Comes out of Resistor

« Last post by JPK on January 23, 2026, 08:09:53 pm »

Should say 4k7. Not 47k. Should read close to 4.7k. If they actually supplied a 47k that's not gonna work. The other one needs to be around 22k. Both 2 watt as my layout shows.

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Tube Amp Building - Tweaks - Repairs / Re: 5E3 Build Smoke Comes out of Resistor

« Last post by stratomaster on January 23, 2026, 07:41:02 pm »

Something at that node is drawing enough current to kill that resistor.  I'd be inclined to think it's the filter cap for that node, but it could be anything there.

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Tube Amp Building - Tweaks - Repairs / Re: 5E3 Build Smoke Comes out of Resistor

« Last post by SEL49 on January 23, 2026, 07:17:03 pm »

The little bag the resistor came in said "2 Watt 47K" and I measured it and it was 47K. I don't know maybe it wasn't a 2 Watt but how would I know? The resistor still reads 47K. What voltage drop might i expect to see over it?

Should be 4.7K, not 47K.

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Tube Amp Building - Tweaks - Repairs / Re: 5E3 Build Smoke Comes out of Resistor

« Last post by apeontheweb on January 23, 2026, 07:13:10 pm »

The little bag the resistor came in said "2 Watt 47K" and I measured it and it was 47K. I don't know maybe it wasn't a 2 Watt but how would I know? The resistor still reads 47K. What voltage drop might i expect to see over it?