Elevate heater trouble

wicked1 · 15th October 2009, 04:04 PM

I'm trying to elevate a 12.6v ct radio shack transformer for an aikido heater supply.
I'm using John's new octal all in one PCB, but am bypassing most of the power supply stuff (he was out of the not all in one PCB is the only reason I got this one)
So, he has places on his PCB for a 300k resistor (to b+), and 82k and a cap (to ground). I connect the center tap to the junction and my transformer starts to smoke! (well, it begins to buzz and get hot, and if I don't immediately unplug it, it smokes).

what am I doing wrong?? I'm trying to test the heater voltage w/out any tubes plugged in. Could this be a problem? I measured the voltage at the voltage divider junction, and its about 75 volts, as it should be. I've tried two transformers, so I don't think it is defective. I plan to make the heaters DC, but right now am just trying to get it to work AC.
the tx does work fine w/out the center tap hooked up to that junction.

I can't figure out what could be causing this!

kevinkr · 15th October 2009, 04:19 PM

Are you sure that the junction of the network is not already connected to one side of the transformer winding? It sounds to me like you are shorting the CT to one of the outer legs of your transformer secondary.

I suspect you do not have to make any connection to that point as I would expect the required connection to be present on the board already.

You can confirm this with an ohm meter.

Incidentally you have compromised the wire insulation in the filament transformer by the apparent short circuit and overheating that occurred so this transformer should probably be trashed now. It's a safety hazard.

You should have a fuse on the primary side to protect against accidents.

wicked1 · 15th October 2009, 04:26 PM

My original tx has been trashed. Im working w/ a new one now that I did have plugged in for a second, but I think is ok.

And I think your comments helped me figure out what's going on. He designed this PCB for DC use, and I'm thinking maybe he has the entire "negative" heater rail connected to that divider junction.

Thanks a lot!

- yep that's it!

15th October 2009, 04:04 PM	#1
wicked1 diyAudio Member Join Date: Jan 2008	Elevate heater trouble I'm trying to elevate a 12.6v ct radio shack transformer for an aikido heater supply. I'm using John's new octal all in one PCB, but am bypassing most of the power supply stuff (he was out of the not all in one PCB is the only reason I got this one) So, he has places on his PCB for a 300k resistor (to b+), and 82k and a cap (to ground). I connect the center tap to the junction and my transformer starts to smoke! (well, it begins to buzz and get hot, and if I don't immediately unplug it, it smokes). what am I doing wrong?? I'm trying to test the heater voltage w/out any tubes plugged in. Could this be a problem? I measured the voltage at the voltage divider junction, and its about 75 volts, as it should be. I've tried two transformers, so I don't think it is defective. I plan to make the heaters DC, but right now am just trying to get it to work AC. the tx does work fine w/out the center tap hooked up to that junction. I can't figure out what could be causing this!

15th October 2009, 04:19 PM	#2
kevinkr diyAudio Moderator Join Date: Sep 2004 Location: Boston, Massachusetts Blog Entries: 6	Are you sure that the junction of the network is not already connected to one side of the transformer winding? It sounds to me like you are shorting the CT to one of the outer legs of your transformer secondary. I suspect you do not have to make any connection to that point as I would expect the required connection to be present on the board already. You can confirm this with an ohm meter. Incidentally you have compromised the wire insulation in the filament transformer by the apparent short circuit and overheating that occurred so this transformer should probably be trashed now. It's a safety hazard. You should have a fuse on the primary side to protect against accidents. __________________ www.kta-hifi.net

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15th October 2009, 04:26 PM	#3
wicked1 diyAudio Member Join Date: Jan 2008	My original tx has been trashed. Im working w/ a new one now that I did have plugged in for a second, but I think is ok. And I think your comments helped me figure out what's going on. He designed this PCB for DC use, and I'm thinking maybe he has the entire "negative" heater rail connected to that divider junction. Thanks a lot! - yep that's it!

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