Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: joesatch on March 29, 2022, 09:05:56 am
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Well i have this PT which i need to get the 28vac wind down to 6.3vac for heaters. According to valve wizard i will need a resistor on one of the legs of the tap. I will be pulling 3.9a total from (2X el34, 3X 12ax7). I need a reduction of 21.7vac from the wind so the resistor looks to be 5.6k? BUT going by valve wizard the Wattage of the resistor needs to be 88 watts! ?? How would you handle this PT dilemma?
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The grey screen print you show is not for a purpose if dropping voltage, it is to make a center tap for heater to keep amp more quiet.
Yes, dropping heater tubes voltage need a powerful resistor.
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The grey screen print you show is not for a purpose if dropping voltage, it is to make a center tap for heater to keep amp more quiet.
Yes, dropping heater tubes voltage need a powerful resistor.
The article certainly is for the purpose of dropping voltage. He shows the different heater configurations and how to drop voltage on each one. As you can see from my photo i have no CT so i circled my scenario in the article
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You are right :BangHead:
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How the heck do i run heaters with this PT? :BangHead:
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How the heck do i run heaters with this PT? :BangHead:
Wiring in series ? No, current is not same between EL34 and 12AX7
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Well i have this PT which i need to get the 28vac wind down to 6.3vac for heaters. According to valve wizard i will need a resistor on one of the legs of the tap. I will be pulling 3.9a total from (2X el34, 3X 12ax7). I need a reduction of 21.7vac from the wind so the resistor looks to be 5.6k? BUT going by valve wizard the Wattage of the resistor needs to be 88 watts! ?? How would you handle this PT dilemma?
It's unreasonable to expect this PT 28v winding to provide 6.3v and 3.9a.
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Well it drove more than that it was driving 4 x 6L6 and 3 x 12ax7. Albeit DC. I was gonna do all DC in series but i have found little to no guidance on DC heaters for power tubes.
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https://www.tubesandmore.com/products/transformer-hammond-low-voltage-filament-open-63-vct
$15
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Well it drove more than that it was driving 4 x 6L6 and 3 x 12ax7. Albeit DC. I was gonna do all DC in series but i have found little to no guidance on DC heaters for power tubes.
So? Copy that scheme.
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To run each of those tubes at 6.3VAC off the same winding, you’re better off with a 6.3VAC winding rated at least 3.9A. That 28VAC winding is likely only rated at 900mA tops and is the wrong voltage for series connection for 2x6L6 and 3x12AX7
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Well it drove more than that it was driving 4 x 6L6 and 3 x 12ax7. Albeit DC. I was gonna do all DC in series but i have found little to no guidance on DC heaters for power tubes.
So? Copy that scheme.
I may do that. Was hoping for an easier route because there's a crapload of components to achieve that.
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I may do that. Was hoping for an easier route because there's a crapload of components to achieve that.
Latole already showed you the simplest, easiest, and most reliable route.
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… there's a crapload of components to achieve that.
More info is required than the circuit snippet shown, eg what’s at the 6V1 node on the 12AX7? It may need to sink, rather than source, current.
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i still have the pcb intact. I'm gonna hook up this 28v tap to it and take some measurements.
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i still have the pcb intact. I'm gonna hook up this 28v tap to it and take some measurements.
Measurements will be meaningless and probably confusing without the tube filaments to provide a load.
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i still have the pcb intact. I'm gonna hook up this 28v tap to it and take some measurements.
Measurements will be meaningless and probably confusing without the tube filaments to provide a load.
You are right.
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More info is required than the circuit snippet shown, eg what’s at the 6V1 node on the 12AX7?
In this thread: https://el34world.com/Forum/index.php?topic=28769.0